The FAO Watershed Management Field Manual is published within the FAO Conservation Guide series as Conservation Guide No. 13 and will consist of eight separate volumes:
Watershed Survey and Planning
Slope Treatment Measures and Practices
Vegetative and Soil Treatment Measures
Roadway Protection Measures
Landslide Prevention Measures
Gully Control (this volume)
The objective of this Manual is to assist professionals concerned with the planning and implementation of watershed management activities by providing practical information supported by examples from a wide variety of situations. However, the watershed situation in each country is unique and it is impossible to provide step-by-step solutions which will apply in any specific case. The user of the Manual is therefore invited to add the local experience and information deemed necessary.
We wish to acknowledge the valuable work of Mr. M.P. Geyik on which this volume was based; it has been edited by Mr. S. Dembner, FAO consultant, and been prepared for publication by Mr. T. Michaelsen of the Forest and Wildlands Conservation Branch. It is hoped that the publication will be useful to all professionals involved in watershed management activities.
The purpose of this document is to provide practical guidance for gully control including a description of the factors affecting gully formation and a classification of gullies. Control measures include diversions and the specifications for various types of check dams and gully plugs.
Now here does the strategy "prevention is the best cure" apply better than in gully control. Gullies usually develop because of an imbalance in run-off conditions, and are almost always due to man's activities. Gully control is therefore often an effort to restore a balance which need not have been destroyed in the first place.
In most cases, gullies can be prevented through good land husbandry - by maintaining infiltration capacity, vegetative cover, soil structure, etc. - and by simple measures to avoid concentration of excess run-off. These are also the measures which ensure good crop yields, growth of forest vegetation and fodder production. The prevention of gully formation is not a burden on the land user but a natural consequence of good land management.
Early interventions are far more economical than late ones. A small gully or rill can easily be repaired. But if the situation is allowed to deteriorate, the same gully may develop into something beyond economic recovery. In most cases, gully control is aimed at preventing further damage and loss of productive land rather than at reclaiming gullied land for agricultural use.
This volume is based on experiences in very steep mountain areas with high intensity rainfall. This has influenced the choice of formulas, examples, etc. Local experience and sound judgment is needed when applying the techniques detailed in the Manual in conditions which vary significantly from those on which it is based. This is of particular importance in the determination of peak flows, construction materials, choice of species and vegetation types.