As stated in the Foreword, the watershed condition in each country is unique and it is impossible to provide detailed survey techniques which are applicable to all cases. This chapter, however, is intended to introduce some of the basic ones and give examples for reference and for stimulation purposes only. Not all of them are required in one project.
The following five sections present more than thirty survey techniques, grouped under twenty-five sub-headings. In addition, a total of twenty-four examples is given in this manual. Most of them are drawn directly from field experience.
The five sections cover:
- land use, land capability and suitability surveys;
- erosion surveys;
- water and other natural resources surveys;
- infrastructure surveys;
- socio-economic surveys.
Land use, land capability and suitability surveys are fundamental for rationalizing land use in a watershed. Following are descriptions of five basic surveys:
- soil survey;
- slope analysis;
- land capability classification and land suitability classification;
- present land use survey;
- land use adjustment survey.
Soil survey needs will have to depend on whether or not there are existing data available. If a standard soil survey has already been undertaken, only some supplemental data will be required. If no such survey has ever been undertaken, there will be a need for a new survey.
When soil information is lacking a new survey must be undertaken. For watershed conservation, the main objective of survey is to provide basic information for land capability classification, and therefore, the survey may be of a relatively simple nature. Such a survey usually includes: identification of major soil types and their boundaries; recognition of problem soils; information on soil depth; and identification and location of limiting factors, e.g. stoniness, waterlogging, occasional flooding, severe erosion, etc.
If the survey is for land suitability classification, further information on soil nutrients, moisture and root zone conditions, as well as on economics, etc. should be collected. Soil survey manuals and guideline books of FAO should be consulted.
Example 1 provides simple guidelines for a soil survey of a watershed in northern Thailand. The work was done by university students under a government project supported by FAO. The field survey, covering a total area of 42 700 ha was completed in 150 man-days. A final report and a 1:15 000 scale map were produced soon afterwards. The objective of the survey is for land capability classification using the "Treatment-oriented system" (see Appendix 2).
Even if a standard soil survey exists, a supplemental survey may still be needed. For instance, soil depth and soil limiting factors are vital to land capability determination yet they may not be shown sufficiently on the existing maps due either to the scale of the map or the nature of the original survey. Also, soil boundaries will need to be re-checked because standard soil surveys usually concentrate on agricultural lands rather than on watershed slopes.
Example 2 describes the working procedures for a supplemental soil survey implemented in a FAO supported watershed project in Jamaica.Slope analysis is an important step towards rationalization of land use in a watershed. It provides the basis for land capability classification, land use planning and soil conservation needs. The "Circle Interception Method" which can be done by office clerks with little training is explained in Example 3. A circle is used because it has equal distance in all directions and hence represents a fixed horizontal distance on the ground. By overlaying a contiguous circle sheet on a topographic map and counting the contour intervals in each circle, one can get the values of the vertical rise.
The slope of a circle can thus be determined by the following equation:
Slope (%) = Vertical rise / Horizontal distance
The diameter of the circle depends on the map scale and contour interval. Too big a circle will represent too great a distance on the ground whereas a circle which is too small will make the work impractical. Diameters of 8 mm to 11 mm have been used satisfactorily on 1:10 000 and 1:15 000 scale maps respectively.
Slopes can be grouped into many categories. As a rule, slope categories should be the same ones used in the land capability classification. Each slope category should be assigned a number or a letter and given a colour for mapping convenience. Example 3 shows the techniques for slope analysis and mapping.
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Example 1 SIMPLE GUIDELINES FOR NEW SOIL SURVEY Technical Guidelines of Soil Survey in the Project Area 1. The purpose of this brief soil survey of the project area (approx. 42 000 ha) is mainly for land capability classification. 2. Major soil groups of the project area should be identified and the boundaries of each marked on the map. To find their boundaries the following procedures can be used:
3. The following soil limiting factors should be looked at closely in addition to the major soil types:
4. Forms and labels: A simple recording form should be made according to this guideline and to be used in the field. Some reference information may be included in the form, for example, site (grid reference), vegetation, topography, etc. The sequences of labels on the soil maps are suggested as follows in each mapping unit:
For example:
5. Final products: 1) A map with soil boundaries, soil depths and limiting factors (scale 1:15 000). 2) An illustrative report. |
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Soils survey information form Code No.: Location: (including grid reference) Soil types: Other types:
Soil depth:
Limiting factors:
Other information:
Date: Surveyor: |
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Example 2 PROCEDURES FOR SUPPLEMENTAL SOIL SURVEY 1. Introduction Jamaica has completed a Soil and Land Use Survey covering the whole island. The reports were issued intermittently by the Soils Department of the Regional Research Centre, University of the West Indies, Trinidad, on an irregular basis since 1958. The soil classification system used in these surveys was rather simple and conventional, compared with the international soil classification systems now existing. Its advantage was that it was based upon almost entirely physical characteristics (texture, structure, colour, depth, drainage, moisture retention, etc.) of the soils which can be easily recognized in the field. The present purpose for producing a soil map is mainly for land capability classification. The Project feels that the existing information can be largely used. Some supplementary items such as soil depths, land use limiting factors will have to be collected in the field. Therefore, taking account of the time constraint, it was decided to use the existing maps as a basis for preparation of a new one. 2. Preparation Before going out to the field, all available reference material and aerial photographs were gathered and studied. Sometimes, a general observation in the field was required. The procedures were: 1) Soil boundaries and other information were directly transferred from annotated photographs to the existing maps of various scale. However, the maps attached to the Parish survey report at a scale of 1:50 000 are the basic material for producing soil maps covering the project area. 2) The existing soil maps were studied and placed over a topographical map in order to distinguish possible inaccuracies in soil boundaries. The boundaries suspected of being inaccurate were also checked using aerial photographs provided by the 3) Limestone and river wash areas can easily be distinguished by the photographs. It was found that, in general, there was estimation of the river wash and an underestimation of the limestone areas. These should be corrected. 3. Field Checking 1) Some soil boundaries were corrected by checking in the field. 2) Soil depths were taken throughout the watershed in order to obtain a general idea of the average soil. depth of each specific soil type in the watershed. On slopes steeper than 30 °, no soil depths are measured. 3) Finally, those areas with severe soil limiting factors preventing intensive land use were indicated on the maps. Soil limiting factors taken into consideration where stoniness, occasional flooding, waterlogging and severe erosion hazards. 4. Final Mapping and Statistics The final soil map was drawn at a scale of 1:10 000. Since the final soil map was allowed to produce in a period of two to three weeks for each unit watershed, it was impossible and undesirable to have great precision and detail. It is important to note that the accuracy of the prepared soil map will not exceed that of the existing map drawn at a scale of 1:50 000 especially regarding soil types and their boundaries. The most important elements for this type of map, however, are soil depths and limiting factors. Finally, statistics were prepared, giving the acreage covered by each soil type or mixture of soil types in the area. This was done by cutting out the different areas of each soil type and weighing them against a reference square of known acreage. |
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Example 3 SLOPE ANALYSIS AND MAPPING 1. Introduction The main objective of slope analysis is to provide the basis for land capability classification and for planning of proper land use and soil conservation treatment. The importance of slope analysis cannot be over-emphasized since this is the first step towards rationalized use of watershed slopes. Many methods are applicable for such analysis: airphotos; slope models; even digitized computers. However, judging from resources available and the manpower conditions in the developing countries, the "Circle Interception Method" is probably most suitable. 2. Materials required
2 Different scale of map, contour intervals and/or diameters of circle need different graphs. However, the procedure to produce a graph is the same. 3. Slope categories Slopes are divided into seven categories or classes in line with the land capability classification criteria. Each class is assigned a colour.
4. Smallest area One circle on the 1:10 000 map equals 1.126 acres (0.45 ha). With the surrounding area of 0.182 acres it becomes 1.3 acres (0.52 ha). The smallest area of 1.3 acre (0.52 ha) was thus adopted because the air photo interpretation of present land use has employed the smallest area of 5 mm by 5 mm, or 1.4 to 1.9 acres (0.56 ha to 0.76 ha) on different scales of photos. Since the circle's diameter represents 250 feet (76 m) on the ground, the slope thus obtained was the average of that distance unless in some occasions two slopes were analysed in one circle. 5. Analysis procedures
7) Draw a final map with slope classes (1 to 7) labelled for each topographical unit. 6. Progress and efficiencyAny draughtsman or person with little experience can be trained to do this kind of analysis work. According to experience, after several days to one week of training, a person could complete about 400 circles an hour. Based on a five-hour working day, 2 000 circles or an equivalent of 2 600 acres (1 040 ha) on 1:10 000 scale map can be completed each day. A small watershed of 25 000 acres (10 000 ha) can be completed in two weeks time (or in ten working days) with a two-man team. SLOPE ANALYSIS GRAPH To be used for Scale. I: 10,000 Contour interval 25 feet. Circle diameter 0•3 inch.
Slope analysis can also be done by using air photographs and stereovision. The photos are first aligned. Specially designed 'slope scale models' are placed on each print and rotated until a sloping dotted line fits the slope to be measured. The angle between the two dotted line is read to determine the actual slope on the ground. The principle employed is that of a variable parallax wedge. It needs an experienced photogrammetrist to do a satisfactory job. Computer programs for terrain analysis are available when Geographic Information Systems (GIS) are used. 3) Land capability and suitability classification Land capability and suitability classification are the foundation of proper land use. Many classification criteria have been developed since the first one was introduced in 1930s by the Soil Conservation Service of the United States. Although capability and suitability are sometimes exchangeable, the former's primary consideration is to prevent land degradation and the latter is to consider the fitness of a given type of land for a defined use (FAO, 1976a). A "Treatment-oriented capability classification" For hilly watersheds, a "treatment-oriented" classification has been used successfully in many developing countries since the 1970s. The characteristics and usage of this classification can be briefly described as follows: - The land is classified according to two major factors: slope and soil depth. When a third factor, soil limiting factor, is present, the land is classified as suitable only for less intensive use. All these factors can be measured or seen on the ground and the process and results of classification can be easily understood by field assistants and farmers. - Each classification is accompanied by land treatment requirements. A piece of land which cannot be treated with prescribed conservation measures should not be used for cultivation or orchards. - Land is classified to its most intensive use permissible. It is permissible for less intensive use but not for over-use. - The classification can be quickly learnt and applied by semi-skilled workers to find lands suitable for cultivation, orchards, pastures or forest at the watershed level either for land use adjustment, settlement or development purposes. It can also be applied readily at the farm level by a field assistant using a hand level to measure slopes and a soil auger to examine soil depths. Appendix 2 shows the classification in a summary form. A detailed report can be seen from Sheng (1972). Example 4 illustrates the procedures for producing a land capability map using this classification system. Figure 6 shows the mapping procedures for producing this type of land capability map and thereafter a land use adjustment map. |
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Example 4 PROCEDURES FOR PRODUCING A LAND CAPABILITY MAP 1.Introduction The procedure is for developing a map based on the treatment-oriented land capability classification system for classifying steep upland watershed! under a homogeneous climatic condition. 2. Some basic principles
3. Procedures
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Land suitability classification is the process of appraisal and grouping of a given area for a specific kind of land use (FAO, 1976a). Economic considerations, among others, are strongly involved in the determination of suitability.
There are several levels of classification according to actual needs for finding varying degrees or categories of suitability. The four categories are as follows:
- suitability order: Indicating whether land is assessed as suitable or not for the major kinds of land use such as rain-fed agriculture, irrigated agriculture, grassland, forestry or recreation. There are two orders represented in maps and reports: S (suitable) and N (not suitable);
- suitability class: Indicating degrees of suitability within order. For instance, S1 (highly suitable), S2 (moderately suitable), S3 (marginally suitable), N (not suitable), etc. To determine the class, economic assessment is needed, i.e. inputs, benefits, and net incomes, etc.;
- suitability subclasses: Indicating kinds of limitation such as m (moisture deficiency), e (erosion hazards), n (nutrient problem), etc.;
- suitability unit: Indicating subdivisions of a subclass. The units differ from each other in their production characteristics or management requirements.
The criteria used can be qualitative or quantitative. Also, the classification can be applied to the current use or potential use. A piece of land can be classified into many objectives according to the needs. Fig. 7 shows a summarized structure of suitability classification and Example 5 shows several suitability maps of the same piece of land. Details can be seen from FAO Soil Bulletin 32: A Framework for Land Evaluation. Suitability criteria for rainfed agriculture, irrigated agriculture, or forestry can also be seen from FAO publications (1983b, 1985, and 1984b).
Present land use and cover type surveys are also fundamental to watershed management. Before beginning this type of survey, several important factors must be predetermined:
- the scale of the map. It should be the same scale as other basic or related maps in order to permit overlays and/or comparisons;
- the scale of air photos. It should be convenient for image transfer;
- determine major land use and cover types to be surveyed and each should be given a mapping symbol. An example is given with the present land use map (page 66);
- decide smallest area for interpretation and mapping.
During the survey, attention should be given to the following:
- at the beginning, close checks should be made to establish the relationship between photo images and actual ground conditions;
- determine major use type for mixed cropping patterns;
- the difference between fallow lands and grasslands;
- the difference between natural and human disturbed areas.
Example 6 shows some details in obtaining aerial photographs, survey procedures and mapping, under a FAO project in Jamaica.
Using computers with image processing techniques and Geographic Information Systems (GIS) can also produce this kind of map. Explanations can be seen in Appendix 3.
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Example 6 USING AERIAL PHOTOGRAPHS FOR SURVEYING PRESENT LAND USE AND MAPPING. 1. Aerial photography The project contracted a Canadian firm to do aerial photography. A brief description of photography and photos are as follows: 1) Before flying and photo-taking by a Canadian firm, 50 triangulation points were marked on the ground by the project. These points were scattered over the project area and some were outside but close to the watershed boundary. 2) The actual photography was done in December 1980. A total of 15 flights were made. 3) Two sets of photographs were obtained in February 1981, one in black-and-white and the other in natural colour. After selection, the final prints of natural colour were obtained in May 1981 in two kinds of colours. The black-and-white set was for producing contour maps. 4) Each set has a total of 230 photos (for 90 000 acres). 5) The photo scale ranges from 1:15 000 to 1:18 000 averaging about 1:17 500. 6) Overlapping of photographs in the flight line was about 65 percent and 75 percent; between two flight lines was 20 percent to 45 percent and these met with the usual standards and requirements. 2. Photo-interpretation The photo-interpretation work was done in July and August 1981. The procedures were as follows: 1) The centre area of each odd (or even) photo was marked for minimizing overlapping of work. 2) Transparent films were placed on every right photo of a stereo pair. Delineation of land use patterns was done with a rapidograph pen. 3) Frequent field checking was made to ascertain the land use types. Usually after a day of delineation in the office, the following day was spent on field checking. 4) Discrepancies between delineation on adjacent air photos, in and between flight lines, were carefully corrected to enable an accurate transfer of information to the photo mosaics. 5) Special remarks on photo-interpretation:
3. Mapping The present land use map indicates various types of information, pertaining to land use at time. However, the accuracy and effectiveness of this map, is dependent on several factors, namely: 1) Availability of up-to-date high quality aerial photographs. 2) Good and thorough interpretation of the photographic imagery. 3) Size of the smallest area which can be shown on the map. 4) Type of transfer method i.e. by eye or by instruments such as a Sketch Master. 4. Materials 1) Aerial photographs: 1:15 000 or 1:18 000 scale natural colour photographs. 2) Mosaics: black and white 1:10 000 scale. These are controlled mosaics produced from the same photos mentioned above. 3) Clear (stable) film, drawing pens, etc. 5. Methodology 1) Gather photographs, mosaics of area (watershed) to be worked on. 2) Secure mosaic to drawing table, or another flat work surface. 3) Overlay and tape down a sheet of clear film. 4) Draw on registration corner marks, boundaries, margins, etc. 5) Depending on which section of mosaic is selected, find the corresponding photograph(s). 6) Observe the land use type or class which has been interpreted and boundaries which have been drawn on the photograph. 7) Identify the said type or class and its area on the mosaic. 8) Carefully and accurately draw the corresponding line or boundary(ies) onto the clear film. The line should be thin and lear. It is best to use a rapidograph pen 0.3 or 0.4 in point size. 9) On completion of a land use type or area, write in the proper symbol.
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Land use adjustment survey is essential for further planning of proper use and conservation needs.
Severely over-used lands should receive priorities for protection and/or adjustment. Under-used lands, especially those which are state or community owned, could be used for settlement or development purposes. Land which is currently used within capability limits may still need soil conservation treatments to ensure its perpetuity.
In obtaining such information, first consideration should be given to the land use policy of the government. For instance, whether or not natural forests (present use) on potentially cultivable lands are considered to be under-used lands and subject to intensive use or for settlement when required. Each use type should consequently be considered against each capability class to rate its degree of over-use, under-use and within-capability use.
After the proper criteria are determined, a map showing land use adjustment needs can be produced by overlaying a present land use map on a land capability map of the same scale (see Fig. 6). The list of criteria and a land ownership map should be kept on hand in the mapping process.
Example 7 shows the mapping procedures, a criteria list together with a sample map for reference.
The map shows the sites and areas of the use conditions. It only indicates the needs of adjustment; any adjustment and conservation plan should depend on further planning actions (see 8.3). Nevertheless, this map will make further development planning much more easy and objective.
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Example 7 PROCEDURES FOR PRODUCING A LAND USE ADJUSTMENT MAP 1. Introduction The land use adjustment map is produced by overlaying a present land use map on a land capability map. It contains information on use conditions such as over-use, under-use or use within capability but needing soil conservation treatment, etc. This kind of information is essential to the watershed planner for making decisions on future land use, adjustment needs, conservation needs, and/or possible resettlement (on public lands). 2. Criteria A classification criterion for determining land use conditions was first worked out. This was produced by comparing present. land use with land capability to obtain the following results (see next page): w+: Use within capability but needs soil conservation treatments. w: Use within capability, soil conservation treatment not necessary. o+: Seriously over-used. o: Over-used. u+: Under-used public lands which can be adjusted for better use, i.e. resettlement. u: Under-used. 3. Methodology (1) Place the coloured present land use map on a light table. (2) Place the transparent sheet of the land capability map on top the present use map and tape down firmly. (3) Examine each parcel of land against its corresponding land capability to determine the land use conditions (w , w, o , o, u , u) by using the above-mentioned criteria as a guide. (4) For determining u+, a land ownership map should be superimposed atop of the two other maps. (5) The smallest unit was about 1.4 acres (0.56 ha). (6) Checking should be carefully done on the symbols and boundary drawings of each piece so classified. (7) Make final mapping with ink and label properly.
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Soil erosion is a major watershed problem in many developing countries. In a watershed there may be many different sources of erosion. The main source areas should have been identified during preliminary investigation stages once identified, a detailed survey should be implemented using criteria and forms developed according to local needs. The main objectives are to pinpoint main erosion sites, define their extent, study their causes and, most importantly, suggest possible corrective or rehabilitation measures.
The survey should be management-oriented rather than academic-oriented. Air photo interpretation plus field checking should generally be sufficient for most erosion surveys. In the following sections five erosion-related surveys are briefly described:
- Geological survey and geomorphological analysis.
- Sheet and gully erosion survey.
- Road erosion survey.
- Landslide investigations.
- Survey of stream erosion and torrent.
Geology and geomorphology of a watershed have significant indications on the fluvial processes of channels and hillslopes and erosion rates. In many countries, geological maps and information may be already available. However, the map scale may often be small and the information is not specific enough to cover the watershed in question. Some rechecking and refinement are usually needed.
If there is no existing information, a brief survey is required. However, the watershed manager should spell out what major data are needed from management point of view and not ask for a general survey which may include unwanted information and take too long a period to complete.
The basic geologic information needed is related to erosion and sedimentation. Rock types, depth of weathering, structures, among others, are the main concerns. For identification of erosion hazards and slope stability, further information should be provided on:
- severe displacement including faults, well-developed joints, extensive fractures, crushed zones, etc.;
- folded areas including anticlines, synclines, and homoclines and their strikes and dips, etc.;
- potential mass movement areas, including weak geological material, talus, recent deposits, dips parallel to slopes, and thin soils over impervious bed, etc.
Geomorphology deals with land forms in a watershed. The fluvial processes of channel development and hillslope evolution are the main concerns for a watershed manager. A survey of land forms will result in a better understanding of the erosion process, hazards, and hence of the management possibilities. For instance, a valley at youth stage will have more active erosion than one at old stage. Hummocky topography at the base of a hill is characteristic of landslide topography. High stream density usually means quick surface runoff and flash floods, etc. This kind of information, together with rock types and structures, permits proper selection of sites for dams and roads as well as estimation of peak flows and timing, etc.
In addition to collection of descriptive land form information, there are some quantitative analysis methods which can be used for comparison or interpretation. Fig. 8 shows some equations used for analysing morphological characteristics. With a reasonably good topographic map there should be no problem in implementing such an analysis for a watershed.
Sheet erosion data may be obtained in several different ways; the determining factors will be time, expenses, and existence of data:
- field investigations including interviewing farmers, checking fence sites and exposed tree roots and comparing soil profiles from adjacent undisturbed areas such as natural forest. Investigation should be carried out carefully and collect as much evidence as possible;
- collection of existing data including erosion data from soil survey reports and data from local experiment stations, etc.;
- setting simple plots with stakes and pins or with soil collection devices such as runoff plots for data supplementary or verification purpose;
- using soil loss prediction equations or erosion models. Care should be given to the validity of equations or models when they are used on steep slopes;
The survey of sheet erosion can be conducted in conjunction with soil survey. Erosion information can simultaneously be shown on the soil map. Example 8 shows a classification of sheet erosion by water used in the USA.
Gullies are comparatively easy to identify on air photos. However, field checking is still needed to ensure proper interpretation. Accurate measurements of gully development (head and channel) need bench mark setting and ground surveying. Whether this is desirable at the planning stage depends on time and resources.
Gullies can generally be classified by their stage (active or inactive), by their form (continuous or discontinuous), by their shape (V-shape, U-shape, etc.) and by their size (small, medium, or large).
Example 9 gives a classification of gullies by depth.
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Example 8 CLASSIFICATION OF SHEET EROSION BY WATER Class 1: Up to 25% of the original A horizon, or original ploughed layer in soils with thin A horizons, have been removed from most of the area. Class 2: About 25 to 75% of the original A horizon or surface soil has been lost from most of the area. Class 3: More than 75% of the original A horizon or surface soil, and part or all of the B horizon or other underlying layers, has been lost from most of the area. Class 4: The land has been eroded until it has an intricate network of moderately deep or deep gullies. Soil profiles have been destroyed except in small areas between gullies. Source: U.S. Soil Conservation Service. |
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Example 9 CLASSIFICATION OF GULLIES BY DEPTHS
Source: U.S. Soil Conservation Service. |
Methodology of sheet and gully erosion surveys and studies can be seen from FAO Conservation Guide 1 (FAO, 1977), Hudson (1981) and Lal (1988).
Road erosion is a major watershed problem. Especially in mountainous countries, improperly constructed and poorly maintained roads often contribute large quantities of sediment to downstream areas through side-slope sliding and road foundation failures.
A survey of road erosion should concentrate on three parts: (1) cut slope, (2) fill slope, and (3) road surface and side ditches. During the survey, the site, problem and magnitude should be analysed and possible control or corrective methods be considered. At the end of the survey, the quantity of various control measures should be estimated. By multiplying each with a unit cost the total cost estimate can be worked out.
Fig. 9 shows the major causes and forms of road erosion and their control measures. Details can be seen in Sheng and Stennett (1975) and FAO conservation Guide 13/4. Example 10 shows a survey form for reference.
Landslides are mostly caused by natural factors, i.e. heavy rains, steep slopes, weak geologic formation, etc. However, in many countries, as development takes place in upstream watersheds, the hazards and damages of landslides also increase. Landslide prevention and rehabilitation therefore becomes an important watershed task.
A landslide is a downward movement of a land mass from a slope. The major landslide forms are fall, slide, slump, flow, creep and their combinations. Many classifications of landslides have been developed; some depend on material and movement, others depend on causes and still others depend on mechanics and age, etc. A local classification can be developed according to actual needs.
Whatever the classification system, it should be practical for watershed management purposes. The following are some points for consideration:
- the classification should be applicable to both natural and artificial slopes, and natural and man-made causes;
- it should facilitate application for both air photo interpretation and field investigation;
- the classification should provide basic information for treatment and rehabilitation needs.
Major survey activities should involve photo interpretation, field checking, recording and mapping. After considering treatment needs and corrective measures for each slide, a cost estimate should be produced.
Example 11 shows a landslide classification and investigation form based primarily on "immediate causes".
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Figure 9 FORMS OF ROAD EROSION AND THEIR CONTROL MEASURES
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Streams usually reflect watershed conditions and respond to major hydrologic events. When the natural equilibrium is lost in a watershed due to people's excessive activities or extremely heavy rains, the stream below will display significant bank cuttings, scouring or sediment deposition. While man can hardly control natural events, efforts to protect the watershed will normally result in less erosion in the streams.
Stream erosion surveys can also be done by air photo interpretations and field checking. In addition to watershed conditions, three items for immediate consideration are bank cutting, channel stabilization and sedimentation. Streams can be classified according to degree or seriousness of erosion in order to determine treatment priorities. Example 12 gives a classification system originally developed by the US Forest Service and modified to suit other countries where more serious stream erosion exists. For streambank protection and water quality control, sometimes a protection belt along streams is needed. To establish the belt needs a survey of present conditions and use. Example 13 gives the width required for the belt on various slopes.
In highly developed or heavily populated watersheds, torrential mountain streams often cause heavy damage to the nearby villages and downstream areas. These streams having steep gradients, extreme fluctuations of flows and massive bedloads are very dangerous and unstable if not controlled.
Techniques for torrent control surveys have been well developed and extensively used in Europe, Japan, and many other countries where villages, hotels, or recreation areas are situated in mountain watersheds. In wildland watersheds or at different socio-economic conditions of less developed countries this kind of work may seldom be practised due to the relatively high cost. Control measures should not only cover streams and adjacent areas where damages may occur but also include the respective tributaries where the torrents start. Control measures usually include vertical and horizontal channel stabilization, bank protection, control of tributary gullies and slides, and revegetation. Detailed torrent control survey techniques can be seen from a FAO publication "Torrent Control".
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Example 12 EROSION CLASSIFICATION FOR STREAMS 1 Class 0: Stream shows no signs of erosion or excesive discharges. Banks well vegetated, often overgrown with woody vegetation. No recent debris or flotsam on banks or lodged in vegetation. Streambed formed of shingle or cobbles, weathered and often discoloured by algae. Pools well developed. Class I: Signs of incipient erosion. Banks undercut and raw in places; fresh sand and sediment in pools; sand-bars active; streamside vegetation may be gone or disappearing. Class II: Accelerated erosion evident, sand bars active, gravel and rocks scoured clean, pools filled with sediment. Streamside debris and flotsam deposited on soil and vegetation well above banks. Some tributaries gullied and depositing fans or deltas in main stream. Class III: Severe erosion. Same symptoms as Class II. but aggravated. Stream bends cutting out actively; bottomland being lost by bank cutting; stream turbid or carrying bedloads most of the time. Class IV: Very severe erosion. Extremely active bank slides and cutting; heavy deposits of fresh bedloads; torrent nature of flows. _________________ 1 A modification of the original classification by H.G. Wilm of the US Forest Service. |
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In any watershed, there exist many kinds of natural resources: water, soil, forest, range, wildlife, etc. Depending on management objectives, many basic surveys or investigations of these resources are needed from which better management plans can be prepared.
In the following sections, brief descriptions of five survey techniques relating to natural resources are given:
- climatic surveys;
- hydrological surveys;
- investigation of water resources and use;
- forest, forest land and agroforestry surveys;
- range, wildlife and recreation surveys.
Climatic surveys usually concentrate on items such as precipitation, temperature, evaporation, humidity and wind, etc. which either affect the water balance and erosion of the watershed or influence vegetation and crop growth of the area.
Most of the data can be collected from climatic stations in a watershed or from stations nearby. However, some compilation and analysis work is usually necessary. The basic information may include the following:
- precipitation: form, amount, distribution, intensity, etc.;
- temperatures: maximum, minimum, mean, frost days, etc.;
- others: evaporation, wind (speed and direction), humidity, radiation, etc.
If there is no such data available, new stations need to be set up. In addition to usual precipitation measurement, some stations may need basic instruments as shown below:
- a standard raingauge plus an automatic raingauge or recorder;
- a thermometer (for maximum and minimum temperature), a hygrothermograph (for continuous humidity and temperature) and/or a psychrometer;
- an evaporation pan and an anemometer.
Rainfall data is probably the most important factor relating to water resources, crop production, runoff and erosion. Three methods are usually used for estimating average rainfall in a watershed. They are 1) arithmetic mean, 2) Thiessen polygon (polygons are formed from the perpendicular bisectors of lines connecting nearby stations), and 3) isohyetal method. Example 14 shows how to apply these methods. For rainfall intensitites, data from automatic raingauges should be used and analysed. A hydrologist or a textbook should be consulted to obtain intensities at different time periods and frequencies. If the only data available are daily rainfall, the following equation can be used to find intensities of various short durations:
where I = rainfall intensities, in mm/hr
R = maximum 24 hour rainfall of 10 year return period
t = duration or time of concentration, in hr.
The constant, 0.6, has been used for rainfall of 10 year return periods. This exponent can be modified to fit local conditions and for different return periods. A monograph and example can be seen from the same series of FAO Field Manual 13/3 (FAO, 1988).
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For most developing countries, the important items in hydrological surveys are streamflow, runoff and sedimentation. Water quality may also be important in some countries.
The data required on streamflow and runoff are: a) peak or flood flow for designing engineering structures, b) low or minimum flow for estimating water supplies and c) annual total and its variation for various planning and design purposes.
Three major conditions may exist for such surveys. The first one is that there are already stream gauging stations established in the watershed with years of records. In this case, work is limited to compilation and analysis.
The second condition is that there are some gauging stations in downstream areas or in neighbouring watersheds. In this case, two methods can be used, given that the gauged watershed and the ungauged one under study are similar in climatic and biophysical conditions:
a) direct transfer: Using simple ratios of the areas of watershed to obtain needed data;
b) regional analysis: Using a statistical approach in which generalized equations, graphical relations or maps are developed for estimating the required information at ungauged sites. For more detailed information, "Water Supply Paper 1543-A" and "Regional Analyses of streamflow characteristics" of the US. Geological Survey should be consulted.
The third possibility is that no gauging stations exist in the same region and therefore no data are available. In this case the following analysis is recommended:
a) field investigation and estimation: For instance, visit the channel and look for and enquire about high water marks to estimate flood flows. This can be done by measuring channel profiles, calculating mean velocity by using the Manning Formula (see Field Manual 13/3), and estimating the corresponding peakflows using the following equation:
Q = AV where:
Q = discharge in volume (e.g. cubic metres per second)
A = cross-section area, in square metres
V = velocity in metres/second;
b) measurement of flowing water, surface floats can be used for rough estimation of velocity. More accurate measurement can be done by using a current meter. On wide streams, many horizontal sections should be divided for individual readings. Once the average velocity is obtained, multiply it by the cross-section to get Q;
c) peakflow estimation: among many equations used, the Rational Formula is still popular in many countries where basic data is lacking. Especially for small engineering structures and local floods this equation should be considered appropriate:
For sample calculations, Field Manual 13/3 (FAO, 1988) can be consulted.
d) new gauging stations: Water level recorders and staff gauges need to be set up to gather data not only for planning purposes but also for future evaluation. Using natural control on the stream as gauging site, a stage-discharge curve (rating curve) should be eventually established for each station. If using artificial control (e.g. on small watershed or for watershed experiment) many formulas can be used. A standard textbook of hydraulics should be consulted;
e) watershed models: some of the popular models have been introduced in Appendix 3.
Sediment is usually divided into two classes: suspended load and bedload. Many methods can be employed for their surveys. Brief descriptions of selected methods follow:
a) Suspended load:
- suspended sediment in a stream can be measured by "sediment samplers". A popular sampler used in the USA for wading measurements is USDH-48. Six to a dozen samples equally spaced across the channel are usually sufficient for smaller streams. Current meter readings are normally made at the same time. For large rivers, measurements are usually done from a cable, a bridge, or a boat;
- for intermittent or ephemeral streams, a multiple stage sampler can be installed along the bank in order to obtain sediment concentrates at different heights of flow;
- for small watershed and plot studies, sample devices such as the "Coshocton Wheel" can be used. It is used in conjunction with an H-flume and takes a certain fraction of run-off for sediment analysis. Simple sediment tanks can also be used for plot studies.
Sediment in the samples can be filtered and dried. The dry weight is expressed as a concentration, in milligrams per litre or ppm (parts per million). To get total suspended load, sample sediment concentrations should be multiplied by stream discharge. A sediment rating curve for a stream should eventually be developed and used for estimation. For detailed methodology, a standard hydrology textbook should be consulted. Also, FAO Conservation Guide 1 and 2 (FAO 1977, 1976) provided some techniques.
b) Bedload:
Bedload is usually difficult to measure, especially on large streams. However, several ways can still be employed for measuring bedload in a small watershed.The simple ones are described as follows:
- for ephemeral streams, a trench across the channel can be dug to trap bedload. Cleaning and measuring need to be done after heavy rains or after filled up;
- behind a check dam, a siltation survey can be made periodically to compare the previous profile and the present one to estimate the rate and the amount of bedload. This type of survey can be applied to any structure where the impounding water is not deep;
- a soil loss or run-off plot will usually collect data on coarse sediment or bedload.
c) Total sediment deposits:
A survey of the cross-sections of reservoirs and ponds against original or previous profiles will provide figures on total sediment deposits over a given time span. A pole, a sounding cable or an automatic depth recorder can be used depending on water depths and budget. Normally, the reservoir management organization carries out periodic surveys and the information can be used for estimating the total sedimentation rate of a watershed. FAO Conservation Guide 2 has detailed descriptions.
This investigation usually covers water budget, water use and use problems and possible solutions.
Each watershed is a hydro-morphological unit which responds to precipitation and energy inputs and produces streamflows and evapotranspiration as outputs. A water balance or water budget concept can be expressed simply in an equation as follows:
Q = P - ET ± S where:
Q = total streamflow or runoff including measured groundwater flow
P = total precipitation
ET = total evapotranspiration
± S = change in storage
This equation represents a normal and balanced picture in which no serious leakage from or to the watershed is occurring. Starting with the driest or wettest month when the soil water storage is believed to be constant from year to year, a water budget of a watershed can be calculated. If all but one component can either be measured (P and Q) or estimated (S at the driest season approaching the wilting point), the application of the equation is relatively simple: ET = P - Q, assuming changes of S in a year period are very small. Potential ET can also be calculated using evaporation data from a pan. Example 15 shows water budgets for two places in Thailand.
Such findings, together with the hydrometeorological data, will give an overall picture of the potential and problems of the water resources in a watershed. For instance, is there sufficient water presently for all the uses? Or in what months is the shortage most severe and what can be done to alleviate it?
Water use includes domestic, irrigation and industrial use. Each one should be investigated as to conditions of present use and predicted future use. For forecasting future use, estimates need to be made on the growth of the population, cropping area, and industry, together with their respective use rates. An example of such surveys at two watersheds in Jamaica can be seen from JAM/67/505 Project Technical Report 13/1 (FAO, 1977a). A brief account of survey items is described under 7.4 (Infrastructure surveys).
Water use by vegetation through evapotranspiration can be estimated as mentioned before. Although applications are still limited, research results have shown that manipulating vegetation can increase streamflow.
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Water use problems usually include water quantity (overall shortage, seasonal shortage, etc.), water quality and legal and economic aspects of water use.
The legal aspects of water use such as various use rights should be investigated.
Related laws or regulations should be reviewed and, if necessary, suggestions
should be made for modifying them or proposing new legislation. Institutional
problems should also be studied and improvements suggested. The cost of using
various types of water should also be reviewed because it affects not only use
rates and the total water resources but also the well-being of the people in
the watershed.
Water shortages of any kind should be investigated. The timing and degrees
of seriousness should be examined and possible solutions suggested. These may
include storing excess runoff during the rainy season in tanks, ponds, small
dams; using additional water harvesting techniques; digging wells; practising
moisture conservation measures on crop lands; or even manipulating vegetation
to increase streamflow.
Water quality problems can be divided into those of chemical, bacteriological
or physical origin. Sediment is probably still the most setious physical problem
in upland watershed areas in the developing world. For chemical and bacteriological
qualities, periodical grab samples should be collected and sent to water treatment
plants or public health centres nearby for analysis. What watershed people should
do is to identify the source or contributing areas. Possible solutions to such
problems may include relocating feed lots, setting stream buffer stripes, and
treatment of factory waste and mining tailings.
Example 16 shows the tolerable turbidity of water for various uses under USA
conditions for reference purpose. A manual on monitoring stream water quality
for land-use impacts (kunkle et a1. 1987) can be a good reference.
The management of forest and forest lands, in most countries, started much earlier than the management of watersheds. In fact, watershed management is a relatively new branch of many national forest departments. Most of the data on forest resources, management plans and forest protection needs should be already available.
Five surveys, however, will be dealt with under this section. They are: 1)
forest roads and logging; 2) protection forest; 3) revegetation needs; 4) hydrologic
conditions of soils, and 5) agroforestry.
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Example 16 TOLERABLE TURBIDITY OF WATER FOR VARIOUS USES
Source: Chang, 1982.
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Forest roads and logging, if not properly operated, may cause serious problems in a watershed. Therefore, a survey of their conditions is usually needed. Example 17 provides sample check lists of them. This example should be used in conjunction with Fig. 9 and Example 10 in Section 7.2 (Erosion Surveys).
Surveys or reviews of the needs of protection forest is often an important part of watershed surveys. In many countries, protection forest was established many decades ago when the socio-economic and technical criteria were very different from those of today. A careful review of the necessity of the existing forest should be undertaken. Usually, new criteria need to be established including consideration of impact on nearby communities and other social consequences.
Additional area or new protection forests are sometimes required in the headwaters of a watershed. Objectives should be well defined - for soil stabilization, water conservation, or flood control - because the required management practices are different in each case. Also, the functions and limits of protection forests should be made clearly known to the community nearby in order to avoid misunderstanding.
Whilst there are no universal criteria for determining the needs for protection forests, the major factors should include slopes; soil (depth and erodibility); geology (rock, structure, etc.); site (headwater, roadside, etc.); and socioeconomic and legal conditions. A point system may be developed to determine whether there is a need for this kind of forest in a watershed.
A survey on revegetation needs should be carried out on any erosive or disturbed areas where protective vegetation cover is needed. The required survey should include:
- logged or cut-over areas;
- eroded areas in forest such as landslides, mined-out and deposit areas, eroded sites along roads and streams;
- special areas which need to be revegetated such as reserved areas, buffer stripes, abandoned squatting areas, over-grazed forest lands, etc.
Based on the survey, a revegetation plan should be prepared including methods (replanting, reseeding, or natural revegetating), species, nurseries, planting or seeding seasons, together with a work programme and cost estimates.
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Example 17 SAMPLE CHECK LIST FOR FOREST ROAD AND LOGGING ASPECTS l. Road aspects 1) Are roads built away from swales, valley bottoms, and elongated depressions? 2) Are roads built on benches, ridges, and toes of slopes where feasible? 3) Do roads avoid seeps, clay beds, slide areas, and steeply dipping formations? 4) Are there adequate buffer strips between roads and streams? 5) Are there natural stream channels altered only where the need is urgent, and only then in accordance with standards? 6) Do gravel and borrow pits contribute to soil displacement and stream pollution? 7) Are cut-and-fill material and debris permitted to reach stream channels? 8) Are road-clearing widths excessive? 9) Are cut-and-fill slopes of proper gradient for soil class encountered? 10) Are cut-and-fill slopes stabilized by mulching, planting, retaining walls, or other measures as necessary? 11) Are fill materials suitable to withstand wet season slump? 12) Are fills compacted by rolling during construction when necessary to ensure stability? 13) Are road surfaces contributing to stream silting by vehicles splashing muddy water into live streams? 14) Are road surfaces crowned to prevent concentration of water on road? 15) Is surfacing material spread over road surface rather than windrowed along edges? 16) Are fill slopes safeguarded from runoff by a protective berm (shoulder, ridge, or curb)? 17) Are culverts (or bridges) of adequate size and length installed at all stream crossings? 18) Are culverts installed on natural slope of the land with headwalls and footwalls as needed? 19) Are bog holes in roads drained promptly after discovery? 20) Is water diverted from roadside drainage ditches sufficiently often to prevent ditch scouring? 21) Are drainage ditches placed above cut slopes as needed to divert runoff from the slopes? 22) Are culverts and drainage ditches cleared of debris prior to rainy season and at other times as needed? 23) Are roads sprinkled and graded as needed during use? 24) Are trails contributing to silting of streams? 25) Are non-system roads closed to public travel and properly treated? 26) Is incompleted construction suitably drained at the end of the work season? 27) Is ditch-blading done so as not to undercut road slopes? 28) Do watershed management staff men review road plans prior to final approval? 29) Are specifications for erosion and water control in the road plan adhered to? 2. Logging aspects 1) Do logging plans specify areas of relatively unstable soil to be protected? 2) Are landings treated to prevent erosion? 3) Are sediment settling basins provided below landings where necessary? 4) Is use of tractors on steep and unstable soils causing erosion and stream siltation? 5) Are tractors used only when soil is firm enough to properly support them? 6) Are tractors kept out of stream channels? 7) Are trees felled or yarded across streams? 8) Do logging practices disperse rather than concentrate runoff? 9) Are skid trails located as far from live streams as feasible? 10) Are skid trails, landings, and spur roads properly drained? 11) Are skid trails and landings reseeded promptly where needed with soil-stabilizing species where this practice is advisable? 12) Are efforts made to scarify and loosen compacted soil in landings and skid trails compacted during logging? 13) Are temporary culverts and bridges removed at end of the logging operation? US Forest Service Handbook 2533. |
Forests with undergrowth and thick layers of litter and humus are very different hydrologically from those without them. Also, different types of soil and different sites have different rates of infiltration. A special survey of the hydrologic conditions of forest soils is needed in many cases for watershed management purposes, especially when flood control or water supply is the main objective.
The survey usually concentrates on the following areas:
- density of the forest and undergrowth;
- kind, density, and thickness of the ground cover;
- soil textures and infiltration rates;
- site conditions including slope, elevation, erosion, etc.
Such a survey may be carried out to cover the soils of entire watershed. Example 18 shows hydrologic soil groupings based on infiltration capacity and texture. Example 19 shows the criteria used in the USA for determining hydrologic conditions of forest and woodland.
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Example 18 HYDROLOGIC SOIL GROUPINGS A. (Low runoff potential). Soils having high infiltration rates even when thoroughly wetted and consisting chiefly of deep, well to excessively drained sands or gravels. These soils have a high rate of water transmission. B. Soils having moderate infiltration rates when thoroughly wetted and consisting chiefly of moderately deep to deep, moderately well to well drained soils with moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. C. Soils having slow infiltration rates when thoroughly wetted and consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately fine to fine texture. These soils have a slow rate of water transmission. D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission. Source: US Soil Conservation Service. |
Survey of agro-forestry needs
Although agroforestry practices have existed in many parts of the world for centuries, it is only recently that the subject has received special attention from forestry, agricultural, environmental and other scientific fields. Agroforestry systems, if properly designed and implemented, can benefit both small farmers and upland watersheds, especially where steep slopes have been misused over decades.
Agroforestry embraces many combinations of trees, agricultural crops and forage. There are also many systems of agroforestry, e.g. agro-silviculture, silvo-pastoral, agro-silvo-pastoral and multipurpose tree production systems, etc. The survey should first identify existing agroforestry activities in the watershed or in the country and examine their real benefits to the farmers as well as their impact on soil and water resources. In addition, survey of agroforestry needs should include the following:
- customs, capabilities and constraints of the farmers;
- appropriate system(s) for local needs;
- marketing possibilities and technological feasibility;
- possible environmental impacts.
Example 20 provides guidelines for surveying environmentally sound agroforestry projects.
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Example 20 ELEMENTS OF SURVEY OF AGROFORESTRY PROJECTS - Survey of needs, customs, and abilities of local people. - Study of both existing and potential markets for future development. - Examination of constraints related to economics, infrastructure, and the potential for organization of local community working groups. - Decisions on which agroforestry systems would be most appropriate for local community needs, the ecological setting, and existing markets. - Selection of management techniques, including planting and harvesting schedules, to maximize yields of both trees and farm crops. - Provisions for monitoring of production and changes in soil fertility; this information should be used as feedback to improve the system. - For intercropping, careful consideration must be given to the following: 1) optimum mixtures and spacing patterns of trees and farm crops, to maximize the production of both. (Particular attention should be given to complementary and conflicting relationships between species); 2) foliage characteristics and leaf fall of the various species, and their influence on competition for solar energy and nutrients; 3) shade tolerance of agricultural species and the effect of forest species on energy levels at the forest floor. Source: Folliott, P.F. & J.L. Thames, 1983. |
In addition to water, forestry and agriculture, many watersheds may have many resources that need to be surveyed and planned for better management or development. In this section, brief descriptions will be given to surveys of rangeland, wildlife and recreation resources.
The major task is to identify the main species of forage crops, measure their productivity and determine carrying capacities of the land. The general conditions of the rangelands in a watershed should also be surveyed in order to permit recommendations for improvements.
Clipped plots are often used for determining the weight of forage over a growing season. The utilization of the plants can either be estimated by percentage or by actual usage. Carrying capacity in terms of animal unit month (AMU) is then determined by the following calculation.
Carrying Capacity (AMU) =(forage produced) (proper use factor) / (forage requirement)
A survey of rangeland conditions also covers the degree of forage utilization, e.g. whether it is overgrazed or not; erosion damage or erosion risk; water supply; soil compactness, infiltration and environmental problems caused by domestic cattle, etc.
First, the wildlife population needs to be surveyed. This can be done by direct aerial counts, driving and counts, or the variable strip method. Indirect methods such as call counts for game birds, ratio methods based on marking of animals or kill data from legal hunting, etc., may also be used. The survey is not merely a count of total numbers but also a measurement of the composition of the animal population.
Second, productivity should be surveyed. Both the hunted and the non-hunted populations should be considered. The results will show the population trend including growth, mortality and diversity, etc. Animal habitats should also be studied, including analysis of extent and location of water and food, and covers for animals or birds. Clearly, any new developments in the watershed should avoid to jeopardize existing wildlife.
Recreation resources are becoming increasingly important in many watersheds of the developing countries, especially those close to urban areas. According to a classic standard used by the US Department of Interior, six classes of recreation areas can be identified, based on their location, activity opportunities, level of development and administrative responsibilities, etc. These may be more applicable to developing countries than many recent classifications. Example 21 briefly defines these six classes.
Recreation sites should be analysed in terms of usage. Estimates should be made regarding the number of visits, length of stay, season of visits and activities, etc. The methodology for estimation includes self-registration, traffic counting and/or using samples and regression analysis.
An environmental impact survey or study may need to be included if intensive use of these areas is foreseen. This is even more important in municipal watersheds where water quantity and water quality are already in critical condition. The study should concentrate on possible damage or disturbance of soil, water, vegetation and other related resources at the sites and in downstream areas. The survey results will provide bases for prevention of camp fire, litter and waste disposal as well as pollution control needs.
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Example 21 SIX CLASSES OF RECREATION AREA: A SUMMARY High density recreation areas: Recreation areas near urban centers, having intensive activities, and requiring considerable investment. General outdoor recreation areas: Areas easily reached from cities, offering extensive and vacation type of activities. Less intensive development than the first category. Natural environment areas: Locations are rather remote, weekend and vacation type activities. Limited development. Outstanding natural areas: Areas valued for sightseeing and study of natural features. Minimal requirements for development. Primitive areas: Development not required or permitted. Historic and cultural sites: Established locations, for sightseeing or studying. Development limited to preservation or restoration. Source: US Department of Interior. |
Infrastructure surveys are always needed for either integrated watershed development or for rural development type of watershed management projects.
Generally, such surveys include the following:
- transportation survey;
- housing survey;
- survey of domestic water supply, irrigation needs and energy;
- survey of public services;
- Survey of agro-industry.
Existing road networks including highways, secondary roads, feeder roads, forest roads, etc., should be investigated. Airphotos may provide part of the needed information whereas other information, e.g. transportation services, traffic and new development plans, etc., can be collected from institutions such as local governments and transportation authorities. Further information should be gathered on road surface conditions, alignment, road gradient, stability of side slopes, drainage problems, and road use and maintenance. Attention should also be given to trails used by animals and farmers. Required improvements such as surfacing (asphalting, ballasting, marling), additional drains (culverts, cross drains), slope stabilization (retaining walls, seeding and revegetation, etc.), adjustment of alignment, gradient improvement together with maintenance practices, should all be included. Such a survey and the road erosion survey mentioned previously can be combined as one if necessary.
A study of present traffic conditions and predicted future trends may point out a need for new roads. If it is needed, a reconnaissance type of survey for the new roads is usually sufficient at this stage to show alternative routes, benefits, and approximate costs.
Transportation facilities and services provided by public and private sectors should also be investigated. The quality of services, transportation cost to the markets and farmer's preference, among others, should also be included.
Housing surveys and planning provide basic information for either new housing schemes or for improvement of existing ones. Many countries may have existing reports on national housing conditions and statistics from population census or physical planning. Such data identifies current housing problems in rural areas as well as future needs according to population forecasts. Based on these data, a localized special survey can be designed. Or, questionnaires on housing can be included in socio-economic surveys.
The survey for rural housing usually includes types of structure; construction material (for frame, wall, floor, etc ); age of the house; rooms per household; total area (sq. m); number of persons per household; ownership; utility; kitchen and kind of stoves; type of toilet; present status; maintenance; and the owner's views on improvement, etc.
Improvement of existing houses may be the major task in many watersheds. Plans fen putting up additional rooms and improving roof and kitchen and toilet facilities can be of great benefit to local residents. Simple designs should be included in the future plan.
Water supply for domestic use is usually the primary concern of the inhabitants. The survey should be designed to identify the present water supply system, if any, and its capacity, delivery, distribution (in yards, into dwellings or at roadsides), and potential for development, etc. Use problems, e.g. quantity, quality, timing, charges, and possible improvements should also be covered in the study.
Where a supply system is insufficient, further investigation of springs, wells and other sources is required to provide a base for planning of new developments or improvements. Possibilities for use of concrete water basins and storage tanks, and applying water harvesting techniques, etc., should also be included.
Usually, minor irrigation and water harvesting can be planned by watershed people with some assistance from irrigation authorities.For irrigation needs, the survey should cover farming systems, cropping patterns, crop water requirement, source of water, distribution systems, energy needs, types of irrigation, and cost and benefit, etc.
An energy supply survey usually covers two main items, power and fuel. Public or private power companies should have statistics of present use and plans for future development. The survey needs to concentrate on the areas without electricity, their present light equipment and fuel and possible improvement.
Fuel for cooking and heating is always a major concern in upland watersheds. Women and children may spend most of their time collecting fuelwood and leaves, etc. On the other hand, the watershed manager is probably concerned about the destruction of forest and ground cover. Such a survey should, therefore, not only identify the kind and quantity of fuel consumed and its cost, but also search for alternative sources and means to alleviate the high labour input and vegetative destruction problems. The need for establishing village fuelwood plots at convenient places is, for instance, one of the subjects to be considered in the future plan.
A general survey of public services in addition to water and electricity is always needed. Services directly related to agricultural production such as marketing, extension services, credit or loan facilities, etc., need to be investigated. Some of the investigations can be combined with socio-economic baseline surveys and institutional studies. Those local services which provide seeds, fertilizers, tools and pesticides, and storage facilities to the farmers through farmers' associations and others may need to be surveyed separately according to actual requirements. The basic information to be collected usually centres around the present service functions, their problems and potential, institutional adjustment needs and other improvement possibilities.
Services for general watershed dwellers may include schools, health clinics, post offices, community centres, etc. The quantity and quality of such services should be analysed and, if necessary, improvements should be recommended.
The possibility of developing agro-industry including cottage industry, merits, in many instances, a special survey. Especially when industrial and special crops are to be introduced in the watershed, a factory or a processing plant will surely induce farmers' production of raw material. Another important benefit of agro-industry is the provision of jobs or seasonal work to the watershed inhabitants including women and youth.
If a new agro-industry is contemplated, the survey should compile human resources data (labour availability, sex, age groups, unemployment, skill, education level, training needs, etc.) as well as physical resources data (water, power, land, raw material, etc.) required for the industry under consideration. In addition, an economic assessment and a financial analysis should be made in order to attract investors. Any potential investment sources should be identified and contacted.
Cottage industries are comparatively easy to start. Sometimes existing small shops can be improved or enlarged. Therefore, an investigation of existing shops and factories and their capabilities and potential is very necessary.
Socio-economic surveys are essential parts of any watershed survey and planning undertaking. Many technically sound projects have failed due to a neglect of socio-economic conditions of the watershed.
Five socio-economic surveys are discussed in the following sections. However, when funds and time pose a limit, one well designed and executed socio-economic base line survey should be considered sufficient in many developing countries.
- Socio-economic baseline survey.
- Demographic survey.
- Land ownership and settlement surveys.
- Survey of farming systems.
- Community development survey.
The subject of socio-economic survey confronts a vast array of social conditions and economic activities in a watershed. Usually, time does not allow for study of each sector in great detail. In many cases, a baseline survey is sufficient for collection of essential data for analysis. Periodical baseline surveys will help to identify the impact of project over time. Depending on project requirements, sometimes specific surveys or studies are further needed in addition to the baseline survey.
Before beginning a baseline survey, a series of decisions should be made on enumeration districts, listing, sampling methods, total samples, number of enumerators needed, survey methods, time and period of survey, data requirements, etc. In addition, important preparatory work such as the design of questionnaires, pre-survey and testing, and recruiting and training of enumerators, etc., should be properly carried out.
At economic part, the main objective of the survey is to collect data from farmers for farm development. Usually, three groups of data are needed:
- Identification of farms: head of the family; location; size; etc.
- Resources of farms: land (soils, slope, etc.); crops (food crops, tree crops, etc.); livestock (cattle, small animals, chickens); farm labour; farm machinery; implements and tools; irrigation water; farm buildings; financial liabilities (loans); and the flow of these resources.
- Utilization of resources: input/output of crops; input/output of livestock; material inputs to farms, general farm activities; off-farm activities; and household consumption, etc.
An FAO publication, "Farm Management Data Collection and Analysis" (Agricultural Service Bulletin No. 34, 1977b), describes such a survey in detail. Example 22 gives a farm summary table.
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For the social part of the survey, the data are needed for basic project designs and for determination of management strategies. If the main objectives of a project are erosion control and conservation farming, for instance, the data requirement may cover the following aspects:
- Basic information: age; educational level; family size; marital status; religion; etc.
- Establishment in farming: years in farming; attitude towards farming, land tenure; family members and time devoted to farming; farm income as percentage of total income; etc.
- Integration in the community: linking with the community; membership in community organizations; source of assistance; etc.
- Identification of farming problems: land too steep; soils too poor; not enough land, labour shortages; lack of credit; lack of technical know-how for improvement; poor marketing; or uncertain rainfall and weather; etc.
- Identification of major needs and priorities: domestic water supply; roads; health services; schools; better homes; marketing; storage; credit; better extension services; more land for farming; irrigation water; employment opportunities.
- Knowledge and attitudes towards soil erosion: understanding and observation of soil erosion; erosion damage on the farm; major causes of erosion; needs for erosion control; farmer's perspective on erosion control methodology; etc.
- Soil conservation skill and needs: knowledge about soil conservation; experience with and willingness to practice conservation farming; preference for certain conservation measures; kind of assistance needed (technical, financial or both); education and training requirements; possibilities for group action.
Many countries undertake demographic surveys or a population census every ten years or so. If recent data are available, they can be used and analyzed without much additional effort. If the last census is out of date, supplementary surveys are needed, but the old census should be used as a base.
The main objective in collecting demographic data is to see the trends in population growth in the watershed. More people means more infrastructure needs such as domestic water, housing and schools, etc., and also means more land, more food, and more jobs. The survey should also identify the movements and composition of the population. These are important to labour supply, settlement needs, youth development, employment for women and other activities in the local community.
The essential data include, but not limited to, the following items:
- Growth trend: crude birth rate; crude death rate; rate of natural increase (per 1 000 persons); etc.
- Migration: out migration; in migration; net balance.
- Composition: sex; age grouping; education level; household size; etc.
- Employment: self-employed; employed; unemployed; employment by occupations, sex and age; number and rate of unemployment; etc. - Predication: population growth; number of persons per household; changes in age structure; unemployment rate and job requirement; etc. This survey can also be incorporated into the socio-economic baseline survey in order to save time and energy.
Land tenure is an important socio-economic factor which greatly affects the farmer's decision regarding land use, land conservation, and farm development. In addition to the baseline survey mentioned above, a land ownership survey should be carried out to provide information for planning purposes. Ownership maps and data can be used for establishing priorities for land conservation and development. For instance, leased or settled public lands should be treated with conservation measures first to serve as demonstrations for private farms. Owner-cultivated farms may receive higher priority than rented lands, etc. Land ownership data will also provide information for land use adjustment and settlement opportunities (see 4.4).
Most of the ownership data should already be available in the government's land department, land valuation office or through local authorities. Depending on time and resources available, an ownership map for a watershed can be prepared with varying degrees of detail. If cadestral surveys have never been done, approximate parcel boundaries should suffice since the map is not intended for legal purposes. If there is no record or no time for sorting out individual parcels, dividing the watershed into two or three categories, e.g. public land (with various agencies), private land, and government settlement and leased land, should be adequate for watershed management purposes.A detailed boundary survey and tenure investigation is very costly and will not be required in most cases.
For a settlement survey, brief accounts of the history and the extent of old settlements are usually needed. Recent settlements in the watershed should be carefully examined. The reasons for settlements, infrastructure provided, size of lots, land use conditions, average incomes, refunds and payments, total cost and benefits, and settler's comments, among others, should be collected and studied. The results will be useful for new settlement planning in the future.
Viewing farm as a whole system, farming systems survey should concentrate on constraints, capacities, farmers' attitudes and the interactions among different components of farming in order to suggest appropriate technology and acceptable improvements. Although it is closely related to ordinary farm management, the approach is not tied to maximization of returns, rather, to understand their systems and thereby suggesting improvements to fit farmers' needs.
For watershed management purposes, a stratified survey of farming systems may be adequate. The items may include the following:
- Systems: rain-fed; irrigation; grazing; mixed; subsistence; others.
- Site: highland; lowland; easily accessible; accessible; inaccessible; erosive; non-erosive; etc.
- Constraints: land; water; labour; age; capital; technical know-how; extension services; access roads; marketing; etc.
- Farming practices: cropping; livestock; irrigation; soil conservation and soil management; production input and output; etc.
- Interactions: between crops and animals; animals and trees; and crops and trees; etc.
- Farming hazards: yield variations; drought; flood; water and wind erosion; pest and disease; etc.
- Attitude, habit, and culture: advanced farmers; fairly advanced farmers; conservative farmers; food habits; work habits; spending and saving habits; degree of self-sufficiency; religious vs non-religious; independent; cooperative; etc.
- Farmer's perspective on improvement needs: more land; more water; more capital; better varieties; labour and capital saving practices; modern farming equipment; improved production efficiency; changing of crop patterns; etc.
As mentioned previously, the inclusion of some community development work in watershed projects can help to win local support.
From the socio-economic baseline surveys, some information can be gathered from the individual farmer on his or her major needs and priorities. However, in a local community, there are many non-farmers and community group members who are interested in the development of the community as a whole. An additional or supplementary survey is sometimes needed to cover the whole spectrum of the community. This can be done either by field visits or correspondence depending on actual needs. Example 23 shows data needs for community development.
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Example 23 DATA NEEDS FOR COMMUNITY DEVELOPMENT Name of village group: number of villages in the group; - Number of households (farmers, non farmers, total); - Population (No.) (male, female over 14 years, children under 14 years, total number); - Living conditions (in numbers of households: good, fair, poor); - Number of households by farm size (<0.5 ha, 0.5-1.0 ha, 1.0-2.0 ha, 2.0-3.0 ha, >3.0 ha); - Ownership (farmowner, tenant, share-cropper, etc.); - Fuel source in percent (collected, fuel forest, oil and others); - Livestock (No.) (draft cattle, water buffalo, dairy cattle, hogs, ducks, chicken and others); - Water supply (No.) (sanitary piped, village wells, individual wells, river and others); - quality of road connections (in village, village to fields, village to village, village to market, village to service centre, etc.); - Schools and education - location and distance (primary village school, district school, middle school, illiterate adults Z); - Home and cottage industry (No.) (bag machine, rope machine, spinning and weaving tools, wood carving and others); - Power tools (No.) (tiller, duster, sprayer, duster-sprayer, thresher, 4-wheel tractor, etc.); - Market (name, distance); - Service centre (name, distance); - Main supply centre (name, distance); - Public facilities (No.) (electricity, telephone, post office, medical centre, hospital, midwife, community centre, public yard, public garden, etc.); - Home gardens - No. and size for (vegetables, fruit trees, fuelwood, etc.); - Village cooperative (consumer, producer); - Village warehouse capacity (square meters, cubic meters); - Village store (No.) (cooperative, individual); - Home improvement (No.) (houses, kitchen, fence, farmyard, storeroom, farm buildings such as cattle shed, tobacco curing shed, silkworm shed, etc.); - Organizations (farm improvement club, home improvement club, youth club, village association, credit union, etc.); - Indebtedness (to government, money lenders, etc.); - Other improvements (according to locality); - Priority of improvements as given by village community. Source: FAO, 1976b. |
