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Gully Treatment _________________________________________________________________________________________________________ United States Part 650 Department of Engineering Field Handbook Agriculture Natural Resources Conservation Service Chapter 10 (650.10) Gully Treatment 1 ENGINEERING FIELD HANDBOOK (650‐EFH) Chapter 10 (650.10) – Gully Treatment Acknowledgments This major chapter revision was prepared under the general direction of Wayne Bogovich, PE, national agricultural engineer, Natural Resources Conservation Service (NRCS), Washington, DC, with assistance from Tony G. Funderburk, PE, agricultural engineer, NRCS, Central National Technology Support Center, Fort Worth, Texas. Extensive comments and edits were supplied by Jon Fripp, PE, stream mechanics engineer, NRCS, Fort Worth, Texas and Kerry Robinson, Ph.D., PE, hydraulic engineer, NRCS, Greensboro, North Carolina. September 2010 2 Table of Contents 1. GENERAL ........................................................................................................................................... 4 DEFINITION ................................................................................................................................... 4 INTRODUCTION ........................................................................................................................... 4 CAUSES ......................................................................................................................................... 4 2. PLANNING .......................................................................................................................................... 5 GULLY TREATMENT BY VEGETATIVE MEANS ................................................................... 6 GULLY TREATMENT BY FILLING AND SHAPING ................................................................ 9 GULLY TREATMENT BY WATER DIVERSION OR RETENTION ....................................... 9 Water Diversion ................................................................................................................ 9 Water Retention .............................................................................................................. 11 GULLY TREATMENT BY GRADE STABILIZATION STRUCTURES ................................ 11 Structural Measures ....................................................................................................... 13 Earthfill Structures with Vegetated Spillway Only ..................................................... 13 SEDIMENT CONTROL WITH DEBRIS BASINS ................................................................... 14 3. SURVEYS ......................................................................................................................................... 14 4. DESIGN GUIDELINES .................................................................................................................... 15 5. INSTALLATION OF MEASURES .................................................................................................. 18 6. MAINTENANCE ............................................................................................................................... 19 References ................................................................................................................................... 20 3 ENGINEERING FIELD HANDBOOK CHAPTER 10. GULLY TREATMENT 1. GENERAL DEFINITION Gully treatment is the stabilization of active gullies by vegetative or structural measures or a combination thereof. INTRODUCTION Gullies can be prevented by such measures as increasing the absorptive capacity of the soil, protecting the land surface and natural drainageways from erosion, and by conducting surface runoff water from fields at a nonerosive velocity through properly prepared and maintained waterways. Besides ruining fertile land, gullies interfere with farm operations, undermine farm improvements, encroach on public highways, endanger livestock, and often mar the beauty and lower the market value of a farm. Materials eroded from gullies reduce the capacity of reservoirs, natural streams, drainage channels and cover bottom lands with deposits of infertile soil. CAUSES Gullies are caused by runoff water cutting, or collecting in, surface depressions and flowing at a velocity sufficient to detach and carry away soil particles. The power to erode increases as the stream increases in size, velocity, and duration. If the depression or drainageway is not protected from erosion a gully will form and be enlarged by each flow through it. Many large gullies have formed because simple steps were not taken to stop them in the beginning. Drainageways which collect runoff water may be natural or may have been caused by: 1. Improperly located farm roads, field and access roads, and trails. 2. Livestock trails. 3. Up-and-down slope cultivation. 4. Unprotected terrace outlets and waterways. 5. Unrepaired breaks in terraces and diversions. 6. Excavated drainage or diversion channels without needed vegetative or structural protection. 4 7. Rilling on bare slopes. 8. Improperly designed and placed road drainage structures. 9. Built-up fence rows or property boundaries. 10. Improper land use, 11. Soluble salts or other adverse runoff water components that destroy vegetation. It is important that the technician be acquainted with those practices and conditions that are likely to start gullying. This will enable him t o assist the landowner in selecting land use changes and cultural measures which will prevent further erosion and help to control existing gullies. 2. PLANNING Gully control can best be attained through a plan that takes into account the treatment of the watershed draining into the gully, as well as treatment of the gully itself. A conservation plan for, or the conservation treatment of, any piece of land should consider all needed and feasible gully stabilization work. The plan may include such practices as critical area plantings, grassed waterways or outlets, grade stabilization structures, diversions, and debris basins. These may be used singly or in combination with other practices to accomplish the following: 1. Interception of runoff water above the gullied area with a diversion or terraces. 2. Retention of runoff water on the drainage area by tillage practices, vegetation and structures. 3. Elimination of the gully by filling and shaping the drainageway with earth moving equipment for critical area planting or grassed waterway development. 4. Revegetation, either by natural processes or by critical area planting and grassed waterway development. 5. Construction of grade stabilization structures to control the grade of the gully and detain or impound water. 6. Complete exclusion of livestock. 7. Control of sediment from active gullies with debris basins. 8. Drainage of seep areas where gully banks are unstable. 5 GULLY TREATMENT BY VEGETATIVE MEANS The objective of most gully control work is to stabilize the gully surfaces by vegetative means. All other measures should lead to that objective, except in areas where rainfall is too low to support a good grass cover. Any gully, regardless of its size or condition, usually will regain a cover of natural vegetation if it is properly protected and is in an area where vegetation will grow readily. Diversion or retention of the water which causes the gully, protection from grazing or trampling by livestock, protection from fire , and the removal of other causes of disturbance usually result in growth of natural vegetation which will, in time, cover the gully and heal the erosion scars. (See Figure 10-1.) Nearly all structural measures used, particularly in grassland areas, depend upon vegetation t o support them and to stabilize the soil exposed to excessive runoff. Of first importance in revegetation is the exclusion of livestock or mechanical disturbance from the gullied area. Most gullied areas or gully banks are not in good condition for vegetative growth since the fertile topsoil has been washed away, slopes are steep, and the battering of raindrops on the unprotected soil has produced conditions adverse to plant survival. Bank sloping may be necessary before vegetation can be expected to do an adequate job of gully stabilization. Adapted grasses, trees, shrubs, or vines provide good protection to gullied areas planned for critical area planting. The possible uses of the area after stabilization will determine the type of vegetation to be established. A stabilized gully may be used as a grassed waterway for terrace outlets, wildlife habitat, woodland area or pasture. It should not be cultivated, burned, or used in a way that will weaken or destroy the re-established vegetation. The best possible use should be selected after considering the size of the gully, its location with respect to other land uses on the farm, the control measures needed, and the type of maintenance required. If it is to be used for a grassed waterway, the gully should be shaped to proper size and proportion. Erosion-resistant grasses should be well established before any terraces are constructed to empty into the channel. Trees, vines and shrubs ordinarily are not used in waterways unless the amounts of water flowing through the channel are relatively small and of infrequent occurrence. Critical area planting of a gullied area in pastureland will be affected by the intensity of grazing on the area. Limited grazing of a grass vegetation during the establishment stage is often beneficial in controlling competitive weeds and shrubs.
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