J. Kövári
Food and Agriculture Organization of
the United Nations
Rome, Italy
1. INTRODUCTION
2. OUTLINE OR FEASIBILITY PLAN
3. DETAILED PLAN
4. ESTIMATES
5. TENDER DOCUMENTS
6. REFERENCES
ANNEX 1 HYDROLOGICAL FORMULAS
ANNEX 2 GENERAL PROVISIONS
ANNEX 3 SPECIAL PROVISIONS
ANNEX 4 CONSTRUCTION OF CHIPATA FISH FARM IN ZAMBIA
ANNEX 5 Bill No........ Construction of Outlets
ANNEX 6 Bill of Quantities and Contract Cost
ANNEX 7 Bidding Schedule
Engineering planning, design and construction of dams, barrages, pumping stations, etc., is normally carried out with a high degree of efficiency. Sometimes, however, the smaller structures, secondary channels, etc., used for aquaculture projects are badly made or omitted entirely from engineering plans. In developing countries engineers have frequently neglected these minor works, particularly those required at the farm level. To contractors they do not mean much profit and they are dispersed and difficult to supervise.
It has been increasingly recognized that one of the major difficulties encountered in the implementation of aquaculture development programmes in developing countries is proper project preparation. Inadequate and poor preparation of projects has often caused the final construction cost of the project to be much higher than estimated. The purpose of this lecture is to present in simple form the various steps required in preparation of plans, estimates and tender documents for projects and to describe some of the planning procedures that are used in these processes.
Project preparation is usually considered to include all those activities short of a final decision to implement. This process includes the following stages:
(i) Identification of the project. At this stage, the production target based on a marketing study, the species to be cultured and the systems of culture to be adopted, the availability of a large enough drainable and accessible land area free from flooding and having adequate soil conditions as well as adequate water source, must all be investigated and determined.(ii) Preparation of outline or feasibility plan of the project.
(iii) Preparation of detailed plan of the project.
(iv) Preparation of estimates of the project.
(v) Preparation of tender documents of the project.
During each stage, a number of activities and analyses must be carried out and the findings used to meet the requirements of the subsequent phase, until the project is finally completed.
2.1 Purpose of Outline Plan
2.2 Procedures for Preparation of Outline Plan
The purpose of an outline plan is to confirm that the proposed project can be economically developed on the selected site, and to investigate and provide all data, calculations and outline plans based on the different investigations required for the project approval and detailed planning.
2.2.1 Site selection
2.2.2 Collection of maps and data
2.2.3 Outline plan
In aquaculture project operations, site selection is of paramount importance. Success of the project depends to a large extent on the proper selection of the site. There are both ecological and technological as well as economic and social considerations involved in site selection. Factors to be considered in site selection are described in more detail in Chapter 1 on considerations in the selection of sites for aquaculture (Pillay, 1977).
The following maps and data about the site should be gathered to facilitate the preliminary investigations and calculations:
(a) Maps- contoured sheet of map at a scale of 1:25 000 to 1:50 000. This can be used for preparation of a project location map, to determine the water catchment area and to serve as a source of information on road connections, etc.;- land map showing boundaries of properties with different ownerships according to the official register of owners;
- soil or geological map showing the topsoil or subsoil encountered at the site;
- water resources development map. This will help in determining the water source of the project by indicating the possibilities of water supply and drainage, as well as by showing the depth of the expected water tables and yield capacities of any aquifers; climatological map showing the meteorological stations nearest to the site and the monthly mean values of temperature and rainfall;
- other development map, if any, regarding the proposed site.
(b) Meteorological data
- mean monthly temperature;
- mean monthly rainfall;
- mean monthly evaporation;
- mean monthly humidity;
- mean monthly sunshine;
- mean monthly wind speed and direction.(c) Hydrological data
- data for discharge, yield, floods and water elevations of existing water sources (rivers, irrigation channels, reservoirs, springs, etc.);- restriction for water supply to the fish farm (for example, periods of the maintenance works in the irrigation channel).
An outline plan is generally used as a basis for approval and financing of a project. This should prove the technical feasibility of the project. The production calculations concerned as well as the design should be in sufficient detail so that a reliable cost estimate including both the annual operational and production cost can be established.
The principal parts of the outline plan consist of the following;
(i) ReportThis should contain the most important information on the project proposal including a description of the site, soil characteristics determined by the reconnaissance soil survey, source of water and the results of the water analysis, meteorological features used for planning, operation plan with the necessary production calculations, planning considerations, arrangement of the layout plan for the ponds and the location of the hatchery and the other buildings with the approach road to the project, arrangement for water supply and drainage of the ponds and the hatchery, the pond facilities, abstract of costs for capital, operational and production costs, economic analysis for benefits, and the proposed construction programme. Additionally, all the statements obtained and required for approval and implementation of the project must be presented usually in a list of annexures to the report.(ii) General location map
This is generally an unsealed map showing the location of the project.(iii) Plane table map
This has a scale of 1:2000 to 1:5000 depending the size of the project, showing the boundary lines and the proposed size of the project, the locations of the soil test pits with their elevations, the rough contour lines and water source and drainage possibilities.(iv) Outline layout plan
This plan to a scale of 1:1000 to 1:5000 should include the arrangements of the ponds, the water supply and drainage systems as well as the location of the hatchery and other buildings including the proposed approach road and the power and telephone lines.(v) Outline cross-sections of dikes and channels
All the typical cross-sections of the dikes and channels showing their measurements and slopes required for the cost estimate must be provided.(vi) List of proposed buildings and equipment
A list of the proposed buildings with their plinth areas and the equipment needed for running the project should be given for the cost estimate.(vii) Soil and water test results
Soil test laboratory results of the samples taken from the test pits for engineering and production purposes should be provided in tables which are used for planning dikes, etc. (Buring, 1979).(viii) Cost estimate
Estimates of base (civil works) cost must be calculated using unit rates judged to be applicable for the region of the project site and major quantities of each item shall be calculated from the drawings in just sufficient detail to serve the needs of proper estimating. Building costs should be estimated on plinth area. Earthwork costs are based as far as possible on a balance between cutting and filling. Estimates of cost are given for electricity supply, engineering (design of detailed plan and supervision of construction), equipment, land procurement and physical contingencies.Lastly, the operational costs and the production cost are provided under separate heads.
(ix) Implementation schedule
Based on the results of the reconnaissance investigations and quantity calculations a bar-chart for the various activities required to complete the detailed plans and tender documents and procure the land for construction should be prepared.
After having approved the outline plan of the project, a review should be made of all data available and, if this is insufficient, action should be taken to rectify the deficiency. Any modifications of the proposed operating schedule and related water management and water requirement calculations for both the fish ponds and the hatchery have to be completed prior to commencing detailed planning.
The topographic survey which has to be carried out at the site selected for a project should be based on a convenient datum marked with a temporary bench mark (TBM) at the site. There are several methods used for topographic surveys. Depending upon the nature and size of the land required for the project, the following methods are the most commonly applied for topographic surveying:
(i) Gridding
(ii) Plane tabling
(iii) Cross-section method with traverse survey
(iv) Radiating lines method with traverse survey
(v) Tachiometry
Methods (i) and (ii) are ideal on relatively flat land, while methods (iii) and (iv) may also be used but are best suited to hilly terrain or use in a narrow, long valley. Tachiometry can be used in either case. The field work in tachiometry is rapid compared with the other methods and it is widely used, therefore, for contouring of any types of areas. With reasonable precautions, the results obtained can be of the same order of accuracy as, or better than, those obtainable by other methods. The following topographic maps and plans are generally needed for a project:
(i) Index or location map
(ii) Boundary map
(iii) Contour map
(iv) Cross and longitudinal sections
(v) Land map
3.1.1.1 Requirements of maps for engineering designs
(i) Index or location mapThis map, which gives general information about the location of the project, the existing roads, railways, towns or other settlements, rivers, lakes, contours, etc., is the most commonly prepared from one of the map sheets scaled at 1:50 000, which may be obtained from the Survey Department Map Sales Depot, or the Survey Department. An example of a location map prepared for the Chipata Fish Farm is shown in Figure 1.(ii) Boundary map
During topographic surveying the boundary lines of the selected area for the project should be fixed by stones or concrete blocks. The boundary lines are usually formed by a closed traverse. The points of the traverse lines are called stations or bearing points (PBR). These may also serve for control of levelling or contouring operations over the site, and for setting out the facilities of the project. The boundary map, as shown in Figure 2, must indicate the lengths of the traverse lines for the boundary of the project, locations of the PBRs, the coordinates of the reference meridian, the bearings of the lines, the actual area covered by the traverse lines, the existing roads, buildings, rivers and other property boundaries. The list of the coordinates of the PBRs, including the elevation as shown in Table 1, should be attached to the boundary map, and the data should be recorded in the construction site logbook before starting any construction works at the site. This is essential as, if the PBRs are destroyed by any machines during the construction period, they can easily be re-established from the site logbook.
Figure 1. Chipata Fish Farm. Location map
Table 1 List of Coordinates and Elevation of PBRs
|
PBR |
Coordinates (m) |
Elevation (m) | |||
|
|
Partial E |
Partial N |
Easting |
Northing |
|
|
6170 |
|
|
492 403.11 |
101 604.34 |
2.241 |
|
6173 |
- 194.26 |
- 68.54 |
492 334.57 |
101 410.08 |
5.544 |
|
6174 |
- 193.57 |
- 68.70 |
492 265.87 |
101 216.51 |
0.880 |
|
6175 |
- 181.20 |
+ 68.59 |
492 084.67 |
101 285.10 |
0.906 |
|
6176 |
- 296.20 |
+111.18 |
491 788.47 |
101 395.28 |
1.158 |
(iii) Contour mapContour maps used in design of the facilities of the project must show the contour lines and all the establishments found at the proposed site such as roads, electric and telephonic lines, rivers and drains or other channels, buildings, underground oil, gas or water supply pipelines, borrow pits, boundary lines, including the location of the PBRs and the TBMs, the north direction as well as the scale used for mapping. The contour map may also show the location of soil sampling stations with numbering. The contour maps, depending on the size of area proposed for the project, should be scaled in 1:1000 to 1:5000.The contour lines should be plotted on the map at 10 cm intervals for flat land and 20 to 25 cm intervals for hilly or valley terrain.
(iv) Cross and longitudinal sections
If a project is established in an area where there are fish ponds, drains and other channels, etc., their cross and longitudinal sections are often required for designing of the new fish ponds or the renovation of the old ones, etc. In such a case, the cross-sections should have a scale of 1:100 and the longitudinal sections should be plotted to a scale of 1:100 vertical and 1:500 to 1:5000 horizontal.(v) Land map
In order to procure the land needed for a project, the required area of the project should be marked by the selected boundary lines on the land map. For procurement of land, the cadastral data of the lands including their owner's names, the size and unit price, as well as total amount in local currency of lands, should be prepared as shown in Table 2.
Table 2 Land Cadastral Data
|
Item |
Land owner's name |
Land |
Land price | |||
|
|
|
Number |
Area (ha) |
Required area (ha) |
Unit |
Total amount |
|
1 |
Shri M.B. Prasad |
900 |
0.154 |
0.154 |
40 000 |
6 160 |
|
2 |
Shri A.K. Sing |
989 |
0.125 |
0.125 |
40 000 |
5 000 |
|
3 |
Shri M.B. Beg |
934 |
0.229 |
0.138 |
45 000 |
6 210 |
|
|
Total |
17 370 | ||||
A detailed investigation of soils is needed to design the facilities of a project. The first step in a detailed investigation is a review of the work already done in the previous project stage. This includes not only a review of the reconnaissance investigations, but also an examination of the reconnaissance design, if any is available, and a determination of whether the objective is still the same. Depending upon the results of the reconnaissance exploration and the size of the project, the requirements for the detailed soil survey must be predetermined. The number and spacing of borings including their exploration depth is dependent upon what is needed to get the data of the soils found in the bore holes at the site. By studying the exploration boring logs available general information on the expected conditions can be obtained. From this the additional number of borings including their spacing distance and exploration depths can be determined. In order to avoid loss of time and money due to boring superfluous bore holes, the following is suggested for preparation of a detailed investigation (U.S.D.I., 1965).
(i) 1 or 2 sample stations to each 2 to 5 ha of the site, should generally be used under uniform soil conditions. More sample stations will be required in variable soil conditions. The Engineer conducting the field exploration work should decide upon the additional number of sample stations.(ii) The depth of each bore hole should be a minimum of 2.0 m below the deepest intended excavation of the project area. The boring depth and the number of sample stations for a special structure, i.e. a large water tower, should be commensurate with the size of the structure.
A number of disturbed and undisturbed samples should be taken from every stratum encountered in the bore holes. The soil samples provide material for an investigation of the soil properties by means of laboratory tests. The results of the soil investigations should be detailed in a report (Terzaghi, 1967).
3.1.2.1 Requirements for soil survey report
The results of the soil survey should be presented in a report. A detailed soil survey report must contain the following:
(i) General reportIn this part, the location of the investigations, methods of boring and samplings, in situ tests conducted at the site, the results of the laboratory tests, the allowable bearing capacity and settlement, the characteristics of the ground water, including whether the water table is perched or normal, its expected fluctuation at the site and quantity of soluble salts or other minerals present as well as foundation and dike construction considerations, should be described in detail.The laboratory tests should provide the required data as listed below for the construction works:
(a) soil consistency
- liquid limit (LL)
- plastic limit (PL)
- plastic index (PI)
- relative consistency (Cr)(b) soil components
- grain size analysis curves coefficient of uniformity (Cu)
- particle size analysis(c) index properties
- water content (w)
- void ratio (e)
- porosity (n)
- dry density (g d)
- wet density (g wet)
- proctor maximum dry density (g Pr)
- absolute specific gravity (Gas)
- apparent specific gravity (Gs)
- cohesion (c)
- angle of internal friction (f)
- allowable bearing capacity (s a)
- modulus of elasticy (E)
- permeability coefficient (k)(d) ground water analysis
- pH
- content of sulphate ion(ii) Location map
Location map should show all the locations of sample stations with their ground elevation.(iii) Logs of sample stations
A log is a written record of the data concerning soils and conditions encountered in individual bore holes. It also provides the results of the laboratory tests on which all subsequent conclusions are based, such as design of the facilities and method of construction. It may form an important part of contract documents and it may be required as basic evidence in court in case of dispute. Each log, therefore, should be factual, accurate, clear and complete. It should not be misleading. The headings on the log forms provide spaces for supplying identifying information as to project, hole number, elevation, dates started and completed, and the name of the person responsible. The body of the log form is divided into a series of columns covering the depth, thickness and description of strata, the presence or absence of water levels as well as the results of the laboratory tests.(iv) Soil profiles
Sections to show the subsurface conditions are used in projects located on hilly terrain. Where soil profiles are provided in the soil report, the information shown in them is limited to factual data such as the ground surface line and logs of bore holes located in their actual position with respect to the ground surface line. Although the choice of sections is made to simplify interpretation, actual locations of features such as water table, etc., are not illustrated by continuous lines, but only where they are encountered in each hole.
3.2.1 Project report
3.2.2 Designs
3.2.3 Criteria for designing pond facilities
3.2.4 Preparation of detailed drawings
A complete report should be prepared covering the project proposal, investigation, the production including its proposed method, engineering features, execution of construction, summary of costs, etc. It should contain a general description of the design including the drawings. The following outline of the items which the report should cover is included as a guide. Obviously, all of the information listed in this outline is not necessary for any particular small project, but the greater part of it will be usually required for a larger project (Alien, 1981).
1. Introduction
This includes the background information and the notes of the proposal.
2. Purpose of project
This should contain the following particulars:
2.1 Type of project
- pilot fish farm
- research fish farm
- training fish farm
- production fish farm(a) fish seed production fish farm
(b) commercial fish farm2.2 Production of project
- proposed cultural method(a) selection of fish species
(b) type of fish culture- monoculture
- polyculture
- main characteristics of production
- production calculation considerations(a) broodstock requirement
(b) survival rates
(c) fry requirement
(d) fingerling requirement
(e) stocking ratio
(f) feed conversion ratio
(g) pond fertilization2.3 Marketing schedule
- methods
3. General information and data
This should include the following particulars:3.1 The project site- location
- accessibility
- communication
- power supply
- land status
- existing improvements3.2 Hydrological data
- design flood
- runoff
- ground water potential3.3 Meteorological data
- mean monthly temperature
- mean monthly rainfall
- mean monthly evaporation
- mean monthly humidity
- mean monthly sunshine
- mean monthly wind speed and prevailing direction3.4 Water source and quality
- description of water source
- statement for water rights or water restrictions
- summary of water analysis3.5 Topography
- summary of topographic survey
- list of the boundary points' coordinates
- list of the temporary bench marks3.6 Soil characteristics
- summary of the soil report
- water table conditions
4. Planning considerations
Design criteria and specifications, description of the facilities, and schedule of execution should be stated in this section of the report.
4.1 Layout of the fish ponds size of ponds
- water depth in the ponds4.2 Water requirement summary of the water demand calculations
4.3 Water supply and drainage systems
- for fish ponds
- for hatchery building
- for additional concrete tanks
- for raceways
- methods for water filtration or water treatments4.4 Description of the facilities
(a) fish ponds
- dikes dike protection
- internal roads
- structures(b) hatchery
(c) pumping station
(d) other buildings
4.5 Description of the construction works schedule of execution
5. Cost estimate and cost of production
(These will be presented in Chapter 4)
6. List of detailed drawings
It should contain all drawings required for the project to be executed. The following drawings are most commonly prepared and enclosed with the project report:6.1 Location map
6.2 Layout plan
6.3 Setting out plan
6.4 Cross and longitudinal sections
6.5 Structural detailed drawings
6.6 Plans of hatchery and other buildings
6.7 Plan of pumping station
6.8 Installation plans
In order to ensure that the detailed plans should be both economical and suitable to the construction, their design must be properly performed. The following designs depending upon the nature and scale of the project usually have to be prepared for the detailed drawings.
3.2.2.1 Hydrological computations
To design a fish farm, located on hilly terrain and fed by water stored in a reservoir or supplied from runoff of the water catchment area, usually will require hydrological computations as follows:
(a) determination of design flood for the spillway of the reservoir to fish ponds or hatchery;(b) runoff of the water catchment area of the project site should be calculated to determine the capacity of the reservoir or the possible area of the fish ponds.
All these calculations based on the local meteorological and soil conditions may be presented using the calculating formulas as shown in Annex 1.
3.2.2.2 Production calculations and pond facilities
Production calculations provided by an Aquaculturist are the most essential parts of the project documents. All statements of production calculations should be considered to prepare any detailed plans of the project. These contain usually the following particulars:
(a) fish farm- production target
- proposed cultural method cultured fish species
- stocking rate- initial weight- requirements of broodstock, fry and fingerling
- proposed harvesting weight
- survival rate
- feed requirements- feed conversion ratio- pond fertilization
- pond management
- operational plan
- marketing plan
- pond specifications- type of ponds- harvesting specifications
- size and number of ponds
- proposed water depth for each type of pond- harvesting method- aeration requirements to the ponds if needed
- requirements of the harvesting facilities(b) hatchery
- production target
- proposed hatchery technology
- operational plan
- specification of facilities
- aeration requirements.
(i) Size and shape of ponds can be defined on the following criteria:(a) Production purpose: based on the species to be cultured in the ponds, the size should be as follows:
|
Type of pond |
Bottom area (ha) |
|
Spawning (S) |
0.01 - 0.5 |
|
Nursery (N) |
0.05 - 2.0 |
|
Rearing and production (R) |
0.25 - 10.0 |
|
Holding (H) |
0.10 - 1.0 |
These ponds, except the rearing and production ones, should be square or rectangular in shape (Woynárovich, 1980).(b) Intensification of production: the higher the production per unit area, the more important becomes the production factor in relation to pond size. Considering the possibility of a larger amount of fish loss during a longer period of harvesting it is advisable to complete harvesting as quickly as possible. It should take no more than one day per pond. The maximum amount of fish which can be handled by an experienced staff with equipment in one day depending on the water and air temperatures, is 10 to 40 tons. This can determine to a large extent the optimal size of the pond, as follows:
|
Level of production |
Production |
Bottom area |
|
|
ton/ha/cycle |
(ha) |
|
Intensive |
8-10 |
1-5 |
|
Semi-intensive |
5-6 |
2-8 |
|
Extensive |
3-4 |
3-10 |
(c) RiskLosses due to epidemic diseases or algae bloom etc., in pond water are more in larger ponds with higher stocking density. It is not desirable to risk more than 10 tons in each pond if any such losses are anticipated.
(d) Marketing schedule
The demand of fish for market may be determined by the optimal size of each production pond.
(e) Harvesting method
To facilitate netting, it is desirable to limit the width of the ponds to about 75 m. However, using a separate harvesting pond or special harvesting box or structure, the width and the shape of the ponds are not limited.
(f) Construction cost
The larger the pond, the lower will be the construction cost per unit area. This is because, the smaller the ponds, the greater is the proportional area occupied by dikes and channels. The construction cost for larger ponds will be lower if their long sides can be oriented parallel to the contours. The steeper the ground gradient the more important it becomes to orient the ponds parallel to the contour. Ponds oriented parallel to the contours also require a shallower cut and a shorter earthmoving haul, which is very important when the ponds have to be constructed with manual labour. The larger the pond, the more difficult it becomes to locate ponds parallel to the contours.
(ii) Water depth in the pond is determined by the following factors:
(a) species to be cultured in the ponds (Chen, 1976; Edwards, 1978; Huet, 1972; Lee, 1973)
|
Species
|
Average water depth in m |
||||
|
S |
N |
R |
H |
||
|
Common carp (Cyprinus carpio) |
0.4 |
0.8 - 1.5 |
1.0 - 2.0 |
1.5 |
|
|
Chinese carps: |
|||||
|
|
Grass carp (Ctenopharyngodon idellus) |
|
|
|
|
|
Silver carp (Hypothalmichthys molitrix) |
|
|
|
|
|
|
Big head (Aristichthys nobilis) |
- |
1.0-1.5 |
1.5-3.0 |
2.0 |
|
|
Mud carp (Cirrhina molitorella) |
|
|
|
|
|
|
Snail carp (Mylopharungodon piceus) |
|
|
|
|
|
|
Indian major carps: |
|||||
|
|
Rohu (Labeo rohita) |
|
|
|
|
|
Catla (Catla catla) |
- |
1.0-1.5 |
1.5-2.0 |
1.5 |
|
|
Mrigal (Cirrhinus mrigala) |
|
|
|
|
|
|
Tilapia species |
0-5-0.6 |
0.6-1.2 |
0.8-1.5 |
1.5 |
|
|
Grey mullet (Mugil cephalus) |
- |
1.0-1.5 |
1.5-2.0 |
1.5 |
|
|
Catfish species |
0.6-1.0 |
0.6 |
1.0-3.0 |
2.0 |
|
|
Black bass species |
0.6-0.9 |
1.0-1.2 |
1.0-2.0 |
1.5 |
|
|
Pejerrey (Basilichthys bonariensis) |
- |
0.8 |
1.2 |
1.2 |
|
|
Colossoma species |
|
1.0 |
1.2 |
1.5 |
|
|
Rhamdia species |
- |
1.0 |
1.5 |
1.5 |
|
|
Eel species |
- |
0.4-0.6 |
1.0-1.5 |
1.5 |
|
|
Freshwater prawn (Macrobrachium rosenbergii) |
- |
|
0.9 |
|
|
|
Rainbow trout (Salmo gairdneri) |
- |
|
1.5-2.0 |
2.0 |
|
(b) Meteorological featuresBoth air and water temperature as well as wind velocity must be considered in determining the water depth in the pond.
In the tropical region, the daily temperature fluctuations are smaller in deeper ponds than in shallow ponds because of the greater ratio between the water surface and volume. This is important because the optimal water temperature required for a higher fish production may be assured with a sufficient water depth. Whereas, in colder areas, such as Europe, where the problem is how to attain higher water temperatures in the ponds more rapidly, the shallower ponds are recommended to achieve a relatively high fish production (Hepher, 1981).
The direction and average velocity of the prevailing winds affect the natural circulation in the ponds which is very important for deeper ponds.
When the water source is solely runoff, sometimes it is necessary to increase pond volumes by increasing depth so as to accumulate enough water during the rainy season to suffice for the entire growing season.
(iii) Pond bottom
In order to drain water completely the bottom of the smaller ponds and the bottom of the internal channels in the larger ponds must be sloped towards their outlet points respectively. A minimum bottom slope of 0.1 to 0.2 % is sufficient
(iv) Dike
Measurements and slopes of the dikes should be determined according to the depth of water in the pond, the size of the pond, soil conditions, construction method and the requirements of transport as well as transit on the dike. The following figures represent good practice:
|
Water depth in the pond |
Top width of dike |
Free board |
|
(m) |
(m) |
(m) |
|
0.50 |
0.50 |
0.40 |
|
0.50 - 0.80 |
0.50 - 1.00 |
0.40 - 0.50 |
|
0.80 - 1.20 |
1.50 |
0.50 |
|
1.20 - 2.00 |
2.00 - 2.50 |
0.50 |
|
2.00 - 3.00 |
2.50 - 4.00 |
0.50 - 0.60 |
Top width for a road used by vehicles should be a minimum of 3.0 m. If there is a feeder channel on the top of the dike, its top width should be wide enough for both the feeder channel and a road or a passage way. The latter is needed for pond operations and maintenance of inlets and feeder channel (Tapiador, 1977).The side slopes of the dikes depend upon the soil conditions, water depth and size of the pond, as well as the expected wave actions. The following slopes are recommended for dikes in various soils:
|
Type of soil |
Inside slope |
Outside slope |
|
Sandy loam |
1:2 - 1:3 |
1:1.5 - 1:2 |
|
Sandy clay |
1:1.5 |
1:1.5 |
|
Firm clay |
1:1 |
1:1 |
|
Inside brick lining |
1:1 - 1:1.5 |
1:1.5 - 1:2 |
|
Inside concrete lining |
0.75- 1:1 |
1:1.5 - 1:2 |
The exposed parts of the dike (outside slope, crown, inside slope above the water level) should be protected by grass against erosion. In ponds with more than about 0,5 ha of water surface, wave protection made of branches, rip-rap, brick lining, bamboo matting, etc. is required at the water level (Stickney, 1979).In order to have a stable dike, a berm with a width of 2.0 to 4.0 m must be left between the dike toe and the drainage channel (Khanna, 1981).
v) Inlet and outlet structures
A fish pond should have separate inlet and outlet structures for water supply and drainage as far as possible. The inlet may be anything from a simple pipe to a concrete sluice. It is very important that the inlet be screened to prevent predatory fish and other animals from entering the pond. The floor level of the inlet is usually higher by a minimum of 0.10 m than the water level in the pond partly to ensure water aeration and partly to avoid escape of stocked fish. Protection must be provided against erosion under and around the inlet. The inlet is better located in the centre of the short side of the pond, in order to provide better water circulation (Hora, 1962).
The outlet should be, generally, on the opposite side to the inlet in smaller ponds. A turndown pipe, open sluice or monk are used as outlet structures. The best type of outlet for controlling water level in the pond and draining the pond is the monk. The monk consists of a vertical tower with three pairs of grooves for housing screens and stoplogs and a horizontal conduit passing across the dike at the lowest level of the pond. It is advisable to provide a harvesting box at the downstream end of the conduit for harvesting the pond without netting. This harvesting box may also be used for breeding or for holding fish for marketing. The size of inlet and outlet should be calculated on the basis of the time needed for filling or draining the pond respectively (Wheaton, 1977).
For designing inlets of ponds the required filling times of different types of ponds can be considered as follows:
|
Type of ponds |
Filling time in days |
|
Spawning |
0.1- 0.3 |
|
Nursery |
0.2 - 0.5 |
|
Rearing and production |
1- 10 |
|
Holding |
0.5 - 2 |
For calculation of the discharge of the feeder channel including intake structure or pumping station the peak water demand has to be considered. The total filling time of all the ponds can be calculated as 6 to 30 days for 5 to 25 ha ponds. The drainage time for different types of ponds should be as follows:
|
Type of ponds |
Drainage time in days |
|
Spawning |
0.2 - 0.4 |
|
Nursery |
0.2 - 0.5 |
|
Rearing and production |
2-8 |
|
Holding |
0.5 - 1.0 |
The total drainage time of all the ponds can be calculated as 5 to 25 days for 5 to 25 ha ponds.The structures used for fish ponds are made of various materials. For designing these structures the durability and maintenance cost of the materials used should be taken into account as follows:
|
Material |
Durability |
Maintenance cost |
|
(years) |
(%) |
|
|
Reinforced concrete (1:2:4) |
20-30 |
100 |
|
Stone rubble in 1:5 cement mortar |
10 - 15 |
150 |
|
Brick masonry in 1:5 cement mortar |
5-10 |
250 |
|
Wooden |
5-8 |
300-400 |
3.2.3.1 Water requirement calculations
The annual water requirements of fish ponds will depend on the soil conditions found at the project site, environmental factors, cultured species and the chosen technology of fish culture. To avoid any difficulty during the operation period of fish ponds all the factors have to be considered in this calculation. The necessary amount of water for a pond in an average year can be calculated using the equation below:
|
Qr = Vf + Vrf + Le + Ls + Lc |
Vra (m3) |
or
|
|
(l/sec) |
where
Qr = annual water requirement (m3 or l/sec)
Vf = A×h = the pond volume to be filled (m3)
A = average water surface area of pond (m2)
h = average water depth of pond (m)
Vrf = No×Vf = the pond volume to be refilled (m3)
No = number of refillings a year
Le = A×E = water loss from evaporation (m3)
E = mean annual evaporation (m)
Ls = A×T×S= seepage loss in the pond (m3)
S = seepage coefficient (m/day)
Lc = Ac×1.2×E = transmission loss in earthen channel (m3)
Ac = water surface area of feeder channel (m2)
Vra = Aeff×Ra = water inflow from rainfall to pond (m3)
Aeff= total area of pond including 70 dikes affected by rain (m3)
Ra = mean annual rainfall (m)
T = operational time in days.
For a hatchery, the peak water demand should be determined considering the production target and hatchery technology proposed (Piper, 1982).
For a raceway system, the maximum flow of water should be calculated. This can be determined from the number of daily water changes in the raceway and the cross sectional area of the raceway (Leitritz, 1980).
3.2.3.2 Hydraulic computations
To avoid overdesigned sizes of hydraulic structures for fish ponds or hatchery, and to assure that their sizes are adequate for smooth operation, hydraulic computations to determine their sizes should be performed, as follows:
(a) for water supply system- design of the main and secondary feeder channels including intake, division boxes, pumping station or syphon, etc.- design of inlets
(b) for drainage system design of outlets
- design of drainage channel including its structures, i.e. culvert, fall, etc.(c) for hatchery
- design of the capacity of pump including its overhead tank design of the water supply pipeline
- design of the drain pipeline
- design of the filter system
To calculate the sizes of the above-mentioned or other hydraulic structures the hydraulic formulas given in Chapter 8 include all the formulas required to determine the sizes of the hydraulic structures. Obviously, the peak water demand based on the production calculations should be considered.
3.2.3.3 Structural calculations
In order to achieve sound hydraulic structures and buildings the structural calculations should be performed.
3.2.3.4 Stability analysis of dikes
The dikes of fish ponds must be safe and stable during all phases of construction and operation of fish ponds. To accomplish this, the following criteria should be met:
(a) the dike must be safe against sliding by water force(b) the slopes of the dike must be stable during construction and under all conditions of pond operation including rapid drawdown of the pond (Creager, 1950)
(c) the dike must be designed so as not to impose excessive stresses upon the foundation
(d) seepage flow through the dike, foundation and structures must be controlled so that no internal erosion takes place and so there is no sloughing in the area where the seepage emerges. The amount of water lost through seepage must be controlled so that it does not interfere with planned project functions.
An earthfill dike designed to meet the above criteria will prove permanently safe provided proper construction methods and control are achieved (Capper, 1978)
To prepare drawings based on detailed investigations and designs, the following should be noted:
- to ensure the most economic solutions and to avoid any delay in construction as a result of shortage of materials, the structures and any buildings should be generally designed with available local materials (Tang, 1979);- to ensure durability of structures and buildings, etc., the best quality materials and workmanship must be used;
- to maintain a high quality of construction, standard local construction techniques should be taken into account when the facilities are designed, and in particular when the measurements of earth works are determined.
3.2.4.1 Requirements of detailed drawings
(i) Location, boundary, contour and land mapsThe requirements of the above maps have been discussed in point 3.1.1.1.
(ii) Layout plan
This plan, depending on the size of the project area, must be scaled in 1:1000 to 1:5000. The layout plan must show the contour lines if those are not provided on a separate contour map and all the establishments found at the site such as the existing roads, electric and telephonic lines, rivers and drains or other channels, buildings, underground pipelines, boundary lines, including the location of the PBRs and the TBMs with their elevations, the North line and the scale used for planning. In addition, the layout plan must show the designed establishments such as fish ponds with their measurements and area as well as the FSL in the ponds, the location of the feeder and drainage channels, all the structures with their mark and number, the hatchery and other buildings needed, the pumping station or other water sources, i.e. wells, etc., the approach road, etc. The characteristic data of the structures such as their mark, size and floor level must be given in a table on the layout plan as shown in Figure 3.
A separate layout plan must usually be prepared for the buildings showing their locations including the internal roads, the measurements and the floor levels of the buildings, etc., their connections to the designed ponds, the North line as well as other facilities, i.e. electric and water supply pipelines, etc. This plan is generally scaled in 1:500 to 1:1000.
(iii) Setting out plan
In order to ensure the accurate marking-out of all the earthworks of the fish farm, a setting out plan must be prepared. The reference line including the TBMs, all the measurements of the fish ponds and drains, as well as feeder canals, including the location and numbering of the cross sections required to peg out the centre lines of the dikes and the channels must be illustrated on this plan as shown in Figure 4. The elevations of the TBMs and other data needed for setting out the facilities should also be given in this plan. The TBMs should be established in such positions that they cannot be destroyed by the machines during the construction period. The scale of this plan is the same, or less, than that used for the layout plan.
(iv) Cross-and longitudinal sections of earthworks
(a) Cross-sectionsCross-sections of dikes, feeder and drainage channels, inner channels and harvesting pits in the ponds should be given in the detailed plans scaled in 1:100. Two types of cross-sections should be noted as follows:
1) Typical cross-sections can be prepared for a smaller project located on flat land. In this case the cross-sections must show all the measurements including their slopes, etc., except their actual height.2) Cross-sections prepared for a medium or larger project should be generally shown for every 50 m of their longitudinal sections including all the dimensions required for their marking out, as well as their actual height. In this case, the section number of cross-sections should be indicated on the drawing. Using these cross-sections, the earthwork calculations for the bill of quantities can be easily done.
In addition to the above, the necessary elevations for both the top of the dikes, the FSL in the ponds and the pond or drain bottoms must be indicated in all the cross-sections. A mark, number or section number must be given to each cross-section. The existing ground level including the instructions referring to the topsoil removal from the basement of the dikes, should be noted on the plan. It is very important that the axis of the dikes and drains, as well as their distances, be illustrated on the drawing.
From time to time when the soil used for construction of dikes has a higher seepage coefficient than required for an impervious dike, a clay core should be designed into the dikes. In this case, the measurements of the proposed clay core including the specifications needed for the core materials must be shown in the cross-sections.In the larger ponds, wave protection has to be provided. Therefore, a typical cross-section of the proposed wave protection in the ponds should be prepared in a scale of 1:50. All the materials, both in quantity and quality, with their specifications should be given in this cross-section.
(b) Longitudinal sections
In general the longitudinal sections are to be plotted in the scale of 1:100 in vertical and 1:500 to 1:5000 in horizontal. They should contain as shown in Figure 5, the length, bottom level in the ponds or in the drains, the location and mark of the structures and dikes, the ground level, the designed crest level of the dikes, as well as the FSL in the ponds. Longitudinal sections will have to be prepared in the following cases:
1) In a barrage pond system for the valley section occupied by:- fish ponds
- each dam of the fish ponds
- the diversion channel2) In a larger contour pond system for the water supply channel, i.e. irrigation channel to the fish farm:
- the main and secondary feeder channels to the fish ponds
- the main and secondary drains
- the inner drains in the ponds
- the dikesThe longitudinal sections including the cross-sections concerned can be used for the quantity calculations of the different earthworks.
(v) Structural detailed drawings
Based on the result of the hydraulical computations and the structural calculations, the detailed drawings of all the hydraulic structures including also the feeder channels as well as the pumping station if needed, must be prepared in the following detail:
1) Layout plan of the structure scaled at 1:50 to 1:200 must show the plan, the required sections and views as well as other details of the structure with all measurements and elevations required for formwork, its connection to the dike and the drain, etc., as well as the quality of the different materials designed for the structure as shown in Figure 6.2) Reinforcement details of the structure as shown in Figure 7 scaled in 1:25 to 1:50 should show all the bars including their spacing and mark in detail sections needed for its construction.
3) Reinforcement plan should give the quality, mark, shape in cm, diameter in mm, number, unit length and total length as well as total weight of bars required for construction of the structure as shown in Figure 8.
The additional detailed plans of the screen, the stoplogs or the installation plans of the pumps for the pumping station, must be prepared in a similar format and detail.
Figure 5. Longitudinal sections - Chipata Fish Farm
Figure 6. Mwekera Fish Farm. Details of outlet
Figure 7. Mwekera Fish Farm. Reinforcement details of outlet
Figure 8. Mwekera Fish Farm
Figure 8. (Cont'd)
(vi) Hatchery buildingBased on the production technology and other calculations, the detailed plans of the hatchery, depending on its output capacity must be prepared in the following detail:
1) Layout plan of the hatchery scaled at 1:50 should show facilities for egg incubation and fry of fingerling holding tanks of spawners, the necessary space for handling and treatment of spawners, storage facilities for feed, equipment as well as laboratory room in which the required chemical and other materials may be stored (Bardach, 1972; New, 1982).2) Plumbing plan should include all the pipelines of both water and air supply to the incubation and rearing facilities showing the materials and size of each pipe including fittings as well as the designed drainage facilities.
3) Installation plans of the incubation and rearing facilities should be separately provided in detail with a scale of 1:10 to 1:50.
4) Reinforcement details of the different tanks and the building as well as other detailed plans needed for construction of the hatchery must be provided in a scale of 1:10 to 1:50.
Before approving a project, the cost of work required must be thoroughly investigated. It is necessary to prepare the cost estimate, for the intended work from the plans and specifications. Thus, an estimate for construction work can be defined as the process of calculating the quantities and costs of the various items needed in connection with the work (Chakraborti, 1922).
Quantity Estimate or Quantity Survey
This is a complete estimate of the quantities of materials or items that may be required to accomplish the project concerned. The quantity estimate is one of the most important ones in order to arrive at an accurate cost estimate for the detailed plan.
Detailed Estimate
Based on the results of the quantity estimate, this includes the cost estimate of everything required for satisfactory completion of work, and should be the best and most reliable estimate that can be made.
Complete Estimate
This is an estimated cost of all items, i.e. cost of main contract or material, labour and supervision, cost of land, engineering fees, miscellaneous, viz. removal costs of owner, contingency percentage, etc., which are related to the work in addition to the detailed estimate.
4.1.1 General abstract of cost
4.1.2 Abstract of cost
4.1.3 Analysis of rates
4.1.4 Quantity estimates
Based on the methods used for the preparation of detailed estimates in different countries, in general the principal parts of the detailed estimates consist of the following:
This includes the name of the project, the date of preparation and the cost of different main sub-headings, including engineering cost of civil works, cost of equipment and land, etc. as well as contingencies. The detailed cost of each sub-heading is not shown in the general abstract of cost.
The estimated cost of each and every individual item of work is calculated by multiplying the quantity by the specified rate in tabular form known as "Abstract form' as shown below, then adding all together to get the actual estimated cost of work. A percentage (1.5 to 2.5 percent) of the above estimate is usually added for a work charge along with an amount (usually 0.5 percent) for tools and plant, to calculate the grand total of the estimated cost.
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S1. |
No. |
Description of item |
Unit |
Quantity |
Rate |
Amount | |
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Total: | ||||||
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1 ½ % for work charge | ||||||
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½ % for tools and plant | ||||||
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GRAND TOTAL: | |||||
In order to ensure that the detailed estimates can be easily surveyed, sub-headings are usually required. In this case, each sub-heading of the estimate is grouped for similar items of work. For an aquaculture project, the sub-headings should be as follows:
(a) Site clearing and preparation(b) Earthwork - this includes excavation, filling, dressing, dewatering, etc.
(c) Concrete work - this includes plain and reinforced concrete works, prefabricated concrete works, formwork for concrete structures, etc.
(d) Brickwork - this includes brickwork in foundation and plinth, brickwork in superstructures, etc.
(e) Stonework - this includes stone work for bed or wave protection and in structures, etc.
(f) Woodwork
(g) Steelwork
(h) Roofing
(i) Water supply and sanitary works
(j) Miscellaneous
(k) Finishing
The abstract of cost should contain the different sub-headings shown separately and added together to show the cost to complete the project.
In order to provide a correct and reasonable rate per unit for a particular item, a detailed surveyed called an "Analysis of rate" should be conducted on costs of materials, labour and equipment as required for the unit following its specification. The rate per unit of an item consists of the following:
(a) Quantity of materials and their costThe quantities of various materials required per unit rate for an item are determined by the specifications. The cost of materials should be the cost on site. To calculate this, an analysis of rates of materials should be calculated separately. This includes the market cost of the materials, including loading and unloading costs, 10 percent profit, and transportation costs.(b) Labour cost
This includes the number of labourers, skilled and unskilled, and their respective wages multiplied by the hours required to complete per unit.(c) Cost of equipment, tools or plant
Wherever possible, the cost of equipment should be allocated to a specific item of rate, i.e. the cost of operating a concrete mixer should be spread over those items for which it is used. For certain tools and plant it is difficult to allocate their use to an individual item of rate, and it is therefore suggested that this expenditure be included in overheads, i.e. establishment charges.(d) Overhead or establishment charges
These include such items as office rent and depreciation of equipment, salaries of office staff, postage, lighting, travel, telephone charges, plans and specifications, etc. They are usually 2 /2% of the net cost of a unit of rate, and may increase to 5 percent.(e) Profit
In general, a profit of 10 percent is calculated for ordinary contracts after allocating all charges for equipment, establishment, etc. For small jobs 15 percent profit and for large jobs 8 percent profit should be considered as common figures.For such items of work for which it is difficult to prepare an analysis of rate, a lump sum (L.S.) rate should be provided in the estimate.
4.1.3.1 Schedule of rates or data for costing
To facilitate the preparation of estimates and to enable them to be prepared in a uniform manner, a schedule of rates or data for costing each kind of work commonly executed is provided by different departments in each country. These usually include general conditions, general specifications, items of different works, data for transportation, materials and labour, method of rate analysis, plant rate analysis and basic unit rate analysis.
As mentioned previously, quantity estimates of items of various works should be prepared to provide an accurate cost estimate for the implementation of a project. Quantity estimates should be prepared separately for both the structures and the earthworks.
(i) Quantity estimates for structures and buildingsMeasurement of all structures and buildings should be taken as per the standard specification, or as per the schedule of rate, or as per current practice.(ii) Quantity estimates of earthworks
The quantity estimates of earthworks, using the plans of cross and longitudinal sections, as well as contour plans if needed, should be prepared. Measurements for earthwork shall be calculated from the relevant drawings.
Calculating formulas
(1) Sectional area having no transverse slope for diking or cutting with same side slopesA = B×d +s×d2, m2
where
B = crest width of dike, m
d = height of diking or depth of cutting, m
s = ratio of side slope as horizontal: vertical(2) Sectional area having no transverse slope for diking or cutting with different side slopes
|
|
m2 |
whereb = base width of dike, m(3) Irregular sectional area
Simpson's rule: divide the sectional area into an even number (n) of parallel strips by means of (n + 1) ordinates, spaced equal distances, d
(first ordinate + last ordinate + 2 S, odd ordinates + 4 S even ordinates)
(4) Volumes of earthwork
(a) Mid section formulaIn this formula, the mean depth or height should be calculated first by averaging the depths of two consecutive sections. From the mean depth the area of mid section should be calculated and volume of earthwork computed by multiplying the area of mid section by the distance between the two original sections. To estimate the quantity of earthwork for a dike or a channel whose level sections are taken at a distance, D, which may be varied depending on the ground level in the longitudinal section of the dike or the channel, a tabular form can be used as shown below:
|
Station |
Height or depth at station (m) |
Mean height or depth (m) |
Sectional area(m2) |
Distance between |
Quantity | |
|
|
|
|
|
stations (m) |
Dike (m3) |
Cutting (m3) |
|
1 |
2 |
3 |
4 |
5 |
6 |
7 |
(b) Trapezoidal or end areas formulaThis method is based on the assumption that the mid area of a pyramid is half the average area of the ends and the end sections are in parallel planes. If A1 and A2 are areas of the ends the volume of the prismoid is given by
Quantity of earthwork may be calculated by trapezoidal formula in a tabular form as shown below
|
Station |
Height or depth at station |
Sectional area |
Mean sectional area |
Distance between stations |
Quantity | |
|
|
(m) |
(m2) |
(m2) |
(m) |
Dike (m3) |
Cutting (m3) |
|
1 |
2 |
3 |
4 |
5 |
6 |
7 |
(c) Prismoidal formulaIf the volume of earth between two successive cross-sections is considered a prismoid, then a more precise formula, the prismoidal formula, may be used. It is generally considered that end sections are in parallel planes.
(first area + last area + 4 S even areas + 2 S odd areas), m3
There are a number of alternative ways in which the prismoidal formula may be used. For instance, it can be used to calculate the volume of excavation in a smaller nursery pond applying the prismoidal formula for a single strip
, m3
where
D = depth of excavation, m
A1 = top area of excavation, m2
A2 = bottom area of excavation, m2
Am = mid area of excavation, m2(d) Volumes from contour lines
This method may be conveniently used where accurate contours are available. The contour interval will determine the distance D in the trapezoidal or prismoidal formula, and for accuracy this should be as small as possible, preferably 0.1 to 0.5 m. The areas enclosed by individual contour lines are best taken off the map by means of a planimeter. In computing the volumes, the areas enclosed by two successive contour lines are used in the trapezoidal formula, whence:
whereV = volume of earth between contour lines A1 and A2
D = vertical intervalThis method can also be used to calculate the volume of water contained in a reservoir, corresponding to a given height. This is done by calculating the total volume contained below successive contours and then plotting volume against height to give a curve from which the volume at intermediate levels may be read.
(e) Volumes from spot levels
This is a method by means of which the earthwork for pond bottom, borrow pits, etc. and similar works with vertical sides may be calculated. Using this method, the area marked out on the contour map should be divided up into squares or rectangles. Elevations are taken at each of the corner points and by subtracting these from the corresponding formation levels, a series of heights is obtained from which the mean height of a series of vertical truncated prisms of earth can be found. The volume of each prism is given by the plan area multiplied by the mean height of the prism. The prisms may, of course, be considered as either rectangles or triangles.
5.1 Advertisement for Bids (Notice to Contractors, or Invitation to Bid)
5.2 Draft Contract
5.3 Statements of Work, Services and Technical Specifications
5.4 Bill of Quantities
5.5 Schedule of Execution
5.6 Bidding Schedule
5.7 Approved Drawings
A tender is a written bid submitted by a Contractor in pursuance of the notification given, to execute certain work at calculated rates with the terms and conditions laid down in the tender documents.
For wide publicity of a major work, the sealed bids concerned are invited by advertising in a minimum of two daily local newspapers. All tender notices should be in the standard form established by the competent department. The advertisement should contain the following information: issuing office, brief description of work, location of project, estimated cost of work, office where plans and specifications can be obtained and charges for them, price of tender form and other tender documents, class of Contractors, earnest money to be deposited, time of completion, date for receipt of bids and time of opening of bids, accepting authority and rights reserved to the Owner. An example of a tender call notice is shown below.
|
ORISSA FISH SEED VIVEKANANDA MARG, BHUBANESWAR-751002 TENDER CALL NOTICE No. CAD-385K: - Managing Director, Orissa Fish Seed Development Corporation Limited. Vivekananda Marg, Bhubaneswar-2, Orissa invites sealed tenders for the following work from the registered contractors of State Public Works (R & B) and Irrigation Departments; Name of work:- Construction of 10 hectare fish seed hatchery project at Chiplima in the dist. of Sambalpur. Tender amount:- Rs. 12,25,191. Cost of tender paper:- Rs. 300 (Son refundable). E.M. 1% of cost of tender paper:- Rs. 12,250. Class of Contractor:- 'A' Class & above. Time of completion:-Twelve months. The tender paper will be sold during the office working days up to 9-12-82 and will be received on 10-12-82 at 2 p.m. and will be opened on the same day at 2.20 p.m. in the presence of the tenderer or their authorised representatives. The earnest money will be duly pledged to the Managing Director, Orissa Fish Seed Development Corporation Limited, Bhubaneswar in shape of N.D.C./N.P.S.C./N.S.C./Orissa Government Loan Bond/ Postal Savings Pass Book/Demand Draft on any Indian nationalised banks at Bhubaneswar, without which tender will be liable for rejection. Certified copy of the Sales Tax and Income Tax clearance certificates are also to be attached and the original to be shown at the time of opening. The authority reserves the right to cancel any or all the tenders without assigning any reason thereof. MANAGING DIRECTOR |
For smaller projects, an invitation for bids is issued by the owner to a selected group of Contractors. It conveys much of the information that would be included in an advertisement. In this case, instructions to bidders should be provided in the letter of invitation to the Employer.
5.2.1 Types of contracts
5.2.2 General provisions or general conditions
5.2.3 Special provisions or special conditions
For implementation of the construction works of a project, an agreement, commonly called a contract, between Owner and Contractor should be concluded which requires that certain legal formalities be observed by the parties. The nature and content of contracts vary from country to country and the terms of the contract should be precise and definite and there should be no room for ambiguity or misconstruction therein. To avoid this contingency, the government department and agencies as well as the Association of Consulting Engineers or the Institutions of Civil Engineers have established standard printed contract forms (Abrahamson, 1969).
Unit-price contract
For unit-price contracts. Contractors are required to quote rates for various items of work on the basis of the corresponding unit price.
Advantages of unit-price contract:
(i) This form of contract ensures a more detailed analysis of cost by the Contractor. The authority concerned with accepting the tender can easily control the rates with reference to its own calculations and decide which of the tenders is favourable.(ii) Since the Contractors are to write rates of individual items in figures as well as in words, it is not easy to form a ring during submission of tender and allot work to one of the Contractors without competition.
(iii) The Contractors work out the unit prices of all items of the Bill of Quantities in order to put them in the bid. Thus, an unworkable rated tender may be avoided, which leads to smooth progress and timely completion of the work.
Lump-sum contract
In this form of contract the Contractor is required to quote a fixed sum for execution of the work completed in all respects. For such a contract, it is very important that the drawings and specifications be comprehensive and show in complete detail all features and requirements of the work.
Advantages of lump-sum contract;
(i) The employer knows exactly what the work will cost.(ii) Detailed measurements of the work executed are not required to be recorded except in respect of additions and alterations.
Contract with lump-sum and unit prices
In this form of contract the Contractor is required to quote partly a fixed sum for execution of an entire structure completely detailed on the drawings, and partly unit prices which may be required for features of variable quantities such as excavation of drains for ponds.
Negotiated contract
When work is awarded on contract by mutual negotiation between the parties without call of tenders, it is said to be a negotiated contract. It may be in any of the forms mentioned above. Advantages of this contract are that it brings some economy in expenditure. The parties selected being always reliable and financially sound, ensure interrupted work with less chance of dispute.
Draft contracts consist of general provisions or general conditions and special provisions or special conditions. The general provisions set forth the rights and responsibilities of the parties to the construction contract and the surety, the requirements governing their business and legal relationships. Particular requirements of the project are separately inserted in the special provisions.
Governments have their own standard general conditions of contract provided on the printed tender form. The conditions specify mainly the following articles:
1. Definitions and interpretation
2. Engineer's representative
3. Assignment and subletting
4. Extent of contract
5. Contract documents
6. General obligations
7. Labour
8. Work materials and plant
9. Commencement time and delays
10. Maintenance and defects
11. Alterations, additions and omissions
12. Property in materials and plant
13. Measurement
14. Provisional and prime cost sums
15. Certificates and payment
16. Remedies and powers
17. Special risks
18. Frustration
19. Settlement of disputes
20. Notices
21. Default of Employer
The general provisions used by FAO in the contract for an aquaculture project as shown in Annex 2 specify the following articles:
1. Nature and interpretation of contract
2. Delays and default
3. Acceptance
4. Copyrights and patents
5. Disputes and arbitration
6. Liability with respect to claims
7. Changes and amendments
8. Termination
9. Notices
There are several articles or clauses in the special provisions of a contract to govern the character of the work to be carried out. Annex 3 shows the general form used by FAO for aquaculture projects which comprise mainly the following articles:
1. Work and services to be executed by the Contractor
2. Equipment, materials, supplies, services and personnel to be provided by the Contractor
3. Schedule of performance
4. Authorizations and permits
5. Levies, duties, taxes, etc.
6. Statement of accounts and/or invoices of Contractor
7. Overpayments
8. Remuneration and method of payment
9. Revision of prices
10. Bonus for early completion and penalties
11. Certificates of completion of works
12. Period of maintenance
13. Completion of period of maintenance
14. Supervision of works
15. Construction site logbook
16. Organization of the construction site
17. Particulars to be supplied
18. Presence of the Contractor on the construction site
19. Insurances at the cost of the Contractor
20. Clearance of site on completion
21. Patent rights and royalties
22. Inspection of site
23. Designation of the Organization's Resident Engineer
Statements of work and services contain the scope of the work including description of the site for work, soil characteristics determined by the reconnaissance soil survey carried out at the site, meteorological features needed for the construction works and the operation of the project, description of the project in detail including the construction works and services required.
The technical specifications contain detailed descriptions of all workmanship, services and materials as well as testing methods which are required to complete a project in accordance with the drawings and specifications.
The specifications required for a project are as follows:
1) Specification of work is required to describe the quality and different materials needed for a construction work and is one of the essential contract documents. In this manner the Contractor can prepare a programme to procure the materials required for a project as well as enabling the Owner's representative (the Engineer) to check the quality of materials, confirming the specifications and thereby avoiding any dispute with the Contractor.2) This also specifies the scope of work and services provided by the Contractor to the Engineer as well as the workmanship, including the method of performing the work. Thus specification of a work serves as a guide both to the Contractor and the Engineer in order to execute the work to their satisfaction.
3) As the rate of work is based on a specification, the Contractor can calculate the rates of various items of works in a tender with his procurement rates of materials and labour. Thus tender documents without specifications of works are baseless;
4) The necessity of specification is to test the quality of materials for the work involved in a project.
5) Specification is an essential contract document and is required for Arbitration or court cases.
The specifications are divided into two types as follows:
Standard specifications
The governmental departments and other public agencies sponsoring public works publish "standard specifications", ensuring a uniformity of administrative procedure and of quality of constructed facilities, as evidenced by specific requirements of materials and workmanship (Merritt, 1968).
Master specifications
In order that the specifications for a particular contract may be completely adaptable to the work of a contract, the standard specifications almost always require modifications and additions. Therefore, master specifications are prepared by design organizations. A master specification covers a particular item of construction, such as excavation of drains, dikes and concrete structures of ponds, etc. It contains requirements for all possible conditions and construction that can be anticipated for that particular item.
Specifications usually are written in the traditional style of composition. They should be prepared with as much detail as necessary to convey that which is required and hence agreed to. Ambiguity and verbosity should be avoided. A good specification is clear, concise and easily understood. The courts have traditionally interpreted ambiguous requirements against the party who prepared them. Since specifications supplement the drawings, the special provisions and standard specifications together should not leave any doubt as to the quality of the required work.
An example of Technical Specifications prepared for the construction of Chipata Fish Farm is given in Annex 4.
A bill of quantities or schedule of quantities consists of a complete list of all various items of works for a project, giving the item number and description of items with unit and quantity of work against each, thus enabling an estimated calculation of price of work. The bill of quantities is prepared from drawings and specifications and is arranged in a tabular form without completing columns of rate and amount. An example of a bill of quantities for construction of outlets is shown in Annex 5.
The work of a project is usually divided into separate elements for payment purposes with respect to the kind of work involved, each element as a separate bill designated as a payment item. The total price of a bid is obtained by summation of the amounts for all items scheduled in the tender, arrived at by multiplying the estimated number of units for each item by the corresponding unit-price bid. A sample summary used for bill of quantities and contract cost is shown in Annex 6.
The Contractor shall complete the work and services of the project to be executed under the contract in accordance with the schedule of execution.
Schedules may be performed in either tabular or graphical form, although the graphical form is generally used because of ease in visualization.
The most widely used graphical presentation of schedule of execution is the rectangular bar chart (Figure 9). It shows starting and completion dates for each item of work. It indicates the items on which work must proceed concurrently, items that overlap others and by how much, and the items that must be completed before work on others can begin. It is a convenient way to advise the Contractor of necessary material delivery dates.
For comparing performance of work with that scheduled, a bar is usually placed above the schedule bar showing actual start and completion dates. The chart in Figure 9 indicates that clearing and preparing of site started on the date programmed and was completed ahead of time whereas construction of outlets began late. At the close of August, construction of outlets was 75% complete. This method has the advantage of being simple. It can be used for a small-scale project, however a more detailed schedule of execution is required for a large-scale project. In this case bar charts have to be separately prepared for performance of work items and others showing materials and different machinery needed for all items of works.
Figure 9. Rectangular-bar progress schedule
The bidding schedule is a very important document on which the contractor summarises his bid including the total price of bid, the load bearing capacity of the soil at the site on which the bid is calculated and confirms as well as signs the terms and conditions of the contract. There are various forms of a bidding schedule. A sample form of this used by FAO for aquaculture projects is given in Annex 7.
One set of approved drawings prepared for the project should be provided with the tender, on which the bidders will be able to control the tender's bill of quantities and calculate their bids. The following drawings have been generally enclosed with the tender documents:
1. Location map of the project, scale 1:50 000
2. General layout of the project, scale 1:2 000
3. Setting out plan, scale 1:2 000
4. Cross-section plan, scale 1:100
5. Longitudinal section of drains, dikes, etc., scale 1:2 000/1:100
6. Structural drawings, including reinforced concrete, scale 1:50
7. Details, scale 1:20
8. Plans of the hatchery and other buildings, scale 1:100
9. Plans of the pumping station, scale 1:500/1:50
10. Electrical installations, scale 1:50
11. Sanitary and other, if necessary, installations, scale 1:50
Further drawings may be issued from time to time at the discretion of the Engineer, as need arises.
Abrahamson, M.W., 1969, Engineering law and the I.C.E. Contracts. London, MacLaren & Sons, Ltd.
Alien, L.J. and E.C. Kinney (eds), 1981, Proceedings of the Bio-Engineering Symposium for fish culture, Bethesda, Maryland, Fish Culture Section of the American Fisheries Society, FCS Publication, 1:307 p.
Bardach, J.E., J.H. Ryther and W.O. McLarney, 1972, Aquaculture: the farming and husbandry of freshwater and marine organisms. New York, Wiley-Interscience, 868 p.
Buringh, P., 1979, Introduction to the study of soils in tropical and subtropical regions. Wayennigen, Centre for Agricultural Publishing and Documentation
Capper, P.-L., W.F. Cassie and J.D. Geddes, 1980, Problems in engineering soils. London, Spon Ltd., 276 p. 3rd ed.
Chakraborti, M., 1982, Estimating costing and specifications in civil engineering. New Delhi (privately published)
Chen, T.P., 1976, Aquaculture practices in Taiwan. Farnham, Surrey, Fishing News Book Ltd., 176 p.
Creager, W.P., J.D. 1950, Justin and J. Hinds, Engineering for dams. New York, John Wiley and Sons
Edwards, D.J., 1978, Salmon and trout farming in Norway. Farnham, Surrey, Fishing News Book Ltd., 208 p.
Hepher, B. and Y. Pruginin, 1981, Commercial fish farming with special reference to fish culture in Israel. New York, Wiley Interscience, 261 p.
Hora, S.L. and T.V.R. Pillay, 1962, Handbook on fish culture in the Indo-Pacific region. FAO fish. Tech. Pap., (14):204p.
Huet, M. and J.A. Timmermans, 1972, Textbook of fish culture: breeding and cultivation of fish. Farnham, Surrey, Fishing News Books Ltd., 436 p. 4th ed.
Kafuku, T., and H. Ikeneone, 1983, Modern methods of aquaculture in Japan. Tokyo, Kodansha Ltd., and Amsterdam, Elsevier, Developments in aquaculture and fisheries science, 11:216 p.
Khanna, P.N., 1981, Indian practical civil engineers' handbook. New Delhi, Engineers Publishers
Lee, J.S., 1973, Commercial catfish farming. Danville, Illinois, Interstate Printers and Publishers, Inc., 263 p.
Leitritz, E. and R.C. Lewis, 1980, Trout and salmon culture (hatchery methods). Calif. Fish. Bull., (164):197 p.
Linsley, R.K., M.A. Kohler and J.L.H. Paulhus, 1979, Applied hydrology. New Delhi, Tata, McGraw-Hill Publishing Co., 689 p.
Merritt, F.S., 1968 ,Standard handbook for civil engineers. New York, McGraw-Hill Book Co., pag. var. 2nd ed.
New, M.B. and S. Singholka, 1982, Freshwater prawn farming. A manual for the culture of Macrobrachium rosenbergii. FAO Fish. Tech. Pap., (225):116 p. Issued also in French and Spanish
Pillay, T.V.R., 1977, Planning of aquaculture development - an introductory guide, Farnham, Surrey, Fishing News Books Ltd., for FAO, 72 p.
Piper, R.G. et al., 1982, Fish hatchery management. Washington, D.C., U.S. Department of the Interior, Fish and Wildlife Service, 517 p.
Stickney, R.R., 1979, Principles of warmwater aquaculture. New York, John Wiley & Sons Inc., 375 p.
Tang, Y.A., 1979, Physical problems in fish farm construction. In Advances in aquaculture edited by T.V.R. Pillay and W.A. Dill. Farnham, Surrey, Fishing News Books Ltd., for FAO, pp. 99-104
Tapiador, D.D. et al., 1977, Freshwater fisheries and aquaculture in China. A report of the FAO Fisheries (aquaculture) Mission to China, 21 April-12 May 1976. FAO Fish. Tech. Pap.,(168):84 p. Issued also in French and Spanish
Terzaghi, K. and R.B. Peck, 1967, Soil mechanics in engineering practice. New York, John Wiley and Sons Inc.
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US Department of Interior, 1965, IBH Publishing Co., 816 p. 2nd ed.
Wheaton, F.E., 1977, Aquacultural engineering. New York, Wiley-Interscience, 708 p.
Woynárovich, E. and L. Horváth, 1980 , The artificial propagation of warm-water finfishes: a manual for extension. FAO Fish. Tech. Pap., (201):183 p. Issued also in French and Spanish
1. METHOD FOR DETERMINING PEAK FLOOD FOR MINOR STRUCTURES
2 To design small dams with small water catchment areas (< 100 km) for aquaculture projects, the peak flood estimate required for the spillway calculations can be determined by the rational formula (Linsley, 1979)
, m3/sec
where
Qp = peak rate of flow, m3/secC = coefficient of runoff
i = rainfall intensity in cm per hour for a given frequency and a duration equal to the time of concentration of the basin
A = water catchment area, ha Values for the coefficient of runoff are given in Table 1.
Table 1 Values of Coefficient of Runoff, C
|
Soil type |
Water catchment area cover | ||
|
|
Cultivated |
Pasture |
Woodlands |
|
Sandy or gravelly soils |
0.20 |
0.15 |
0.10 |
|
Loams |
0.40 |
0.35 |
0.30 |
|
Heavy clay soils or soils with a clay pan near the surface; shallow soils above impervious rock |
0.50 |
0.45 |
0.40 |
The time of concentration, Tc, is the time it takes for water to flow from the most distant point in the water catchment area to the outlet point. An equation for estimating this characteristic follows.
where
Tc = time of concentration in hoursL = length of the water catchment area along the main stream from the outlet to the most distant ridge in km
H = the difference in elevation between the outlet and the most distant ridge in km.
In areas where rainfall records are lacking, the time of concentration can be calculated to arrive at the duration of the design storm.
2. METHOD OF ESTIMATING ANNUAL UNIT WATER YIELD FOR UNGAUGED WATER CATCHMENT AREAS
In order to determine the annual water yield estimated from a catchment area where there is not enough data to make an accurate calculation, the following formulas proposed by Brenken can be used:
|
Region |
Formula |
|
Arid |
qA = 0.0555 R - 55 |
|
Subtropical |
qA = 0.373 R - 47 |
|
Tropical |
qA = 0.336 R - 179 |
|
Monsoon |
qA - 0.963 R - 630 |
where
qA = estimated annual unit water yield in mm
R = mean annual rainfall in mm
Contract No.
Article 1 - Nature and Interpretation of Contract
(a) The Contractor shall, for the purposes of this Contract, have the status of an independent contractor and shall be fully responsible, in particular, for acts or omissions of his employees. The Contractor and his employees shall conform to all applicable laws and regulations; he shall promptly correct any violations thereof and shall keep the Organization informed of any conflicts or problems arising in relation to the authorities of the country concerned.(b) The Contractor shall have the sole and full responsibility for the performance of his obligations under this Contract; except as may be provided for in this Contract or in a written authorization by the Organization, the Contractor shall not enter into any subcontracts or otherwise assign, transfer or charge to any third party any of his rights or obligations under this Contract.
(c) Nothing in this Contract or relating thereto shall be construed as constituting a waiver or privileges or immunities of the Organization, nor as conferring any privileges or immunities on the Contractor or his employees.
(d) No official, employee, or other representative of the Organization shall have any share in this Contract, or receive any benefit therefrom.
(e) In the event of any conflict or inconsistency between the provisions of Section I and Section II of this Contract, the former shall prevail.
Article 2 - Delays and Defaults
(a) If there should be any delay in the performance of this Contract or any part thereof, the Contractor shall notify the Organization in writing giving the cause, such notification to reach the Organization no later than ten days after the date on which the delay is known by the Contractor.(b) If the Contractor is unable to obtain any materials or services necessary for the performance of the Contract from his normal sources of supply, he shall remain liable for any delays when equivalent material or services can be obtained from other sources in good time.
(c) In any event, if the Contractor fails to make delivery of the material or to complete items or services required within the time specified in the Contract, or within any extension that may be granted, the Organization may, without prejudice to any further rights it may have under this Contract and in particular under Article 8 of this Section:
(i) Suspend or cancel the right of the Contractor to proceed further with any items or services - or part thereof - in which there has been a delay;(ii) Obtain elsewhere upon such terms and conditions as may be deemed appropriate, replacement items or services similar to those which the Contractor failed to provide; and
(iii) Make a corresponding adjustment to the consideration payable to the Contractor;
provided, however, that the Contractor shall continue performance of the Contract to the extent not suspended or cancelled under the provisions of this paragraph.
(d) The Contractor shall be liable for any excess costs or damage caused to the Organization by a failure or delay on the part of the Contractor in the performance of his obligations under the Contract, except where such failure or delay is due to:
(i) causes which are attributable to the Organization;(ii) any unforeseen cause beyond the control of and without the fault or negligence of the Contractor, including but not limited to acts of God, acts of Governments, fires, floods, epidemics, quarantine restrictions, strikes, lock-outs, and freight embargoes.
(e) If, in the event of a default by the Contractor or a delay attributable to him, the Organization is of the opinion that the determination of actual excess costs or damages, or any part thereof, incurred by the Organization is not practicable, the Organization may require the Contractor to pay, in lieu of or in addition to actual damages, as the case may be, the amount specified in, or to be calculated in accordance with, the relevant provision of Section 1 of this Contract, as fixed, agreed and liquidated damages for the duration of the delay or default.
(f) The Organization shall determine the effects of any delay or default particularly in regard to an adjustment of the consideration due to the Contractor and to excess cost or damages caused to the Organization and its findings shall be binding, provided always that the Contractor shall have the right to avail himself of the provisions of Article 5 of the section.
Article 3 - Acceptance
(a) The Organization may examine any item, equipment, materials, supplies and/or services to be provided under this Contract, at any time prior to expiry of this contract.(b) The Organization may reject any item, equipment, materials, supplies or services or may require alterations thereto or replacements thereof as a condition for acceptance, and its findings shall be conclusive except in regard to defects or fraud which may appear later.
(c) Should the Contractor be unwilling to accept any decisions made under (b) of this Article, he shall have the right to avail himself of the provisions of Article 5 of this section.
(d) If this Contract specifically requires the Contractor to procure equipment, materials or supplies on behalf of the Organization, such procurement shall be of new equipment, materials or supplies unless procurement of used equipment, materials or supplies is approved in advance in writing by the Organization.
Article 4 - Copyrights and Patents
(a) The copyrights of each and any related part of the work to be performed under this contract shall be vested in the Organization including, without any limitation, the rights to use, publish, sell, or distribute, privately or publicly, any item or part thereof.(b) The Contractor shall defend and hold the Organization, its employees and agents free from any liability whatsoever, for or on account of the use or infringement of any copyright, patterns, trade mark, personal or private right, or the right of any Corporation or Association in connection with this Contract.
(c) The Contractor hereby warrants that he has the right to grant the copyright and other rights referred to in this Contract to the Organization and that the materials shall be free from unlawful matters.
(d) Should any claim arise out of an infringement of any third party right whatsoever the Contractor shall be responsible for settlement and he shall indemnify the Organization against all loss, injury or damage, including any legal costs or expenses, properly incurred by or occasioned to the Organization as a result of any break of the warranty mentioned in paragraph (b) above.
(e) Any copyright or other rights, patent or other protection which is to be excepted from the operation of this Article shall be specifically stated in Section I.
(f) The covenants and warranties specified in this Article shall not apply to material which the Organization has furnished to the Contractor.
Article 5 - Disputes and Arbitration
(a) Except as otherwise provided in this contract, any dispute between the Contractor and the Organization arising out of this Contract shall be settled by mutual agreement between the contracting parties.(b) If the contracting parties are unable to reach an agreement on any question in dispute or on a mode of settlement other than arbitration, either party shall have right to request arbitration in accordance with the rules set forth for this purpose, by the International Chamber of Commerce.
(c) The parties agree to be bound by any arbitration award rendered in accordance with the above paragraph, as the final adjudication of any such dispute.
Article 6 - Liability with respect to Claims
(a) The Contractor hereby indemnifies and holds the Organization harmless from and against any and all responsibilities, claims, demands, suits, judgements, damages and losses, including the costs, fees and expenses in connection therewith or incident thereto for:(i) any injury to his employees and third parties(ii) any loss of, damage to, or destruction of any property of third parties; arising out of, or in any way connected with the performance of the work and services of the Contractor under this Contract.
(b) The Organization may, where in its opinio
