fctsht54 Dam S/Ground Cover - Association of State Dam Safety ...

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fctsht54 Dam S/Ground Cover - Association of State Dam Safety ...

OHIODEPARTMENTOF NATURALRESOURCESDIVISION OF WATEROhio Department of Natural ResourcesDivision of Water Fact SheetFact Sheet 99–54Dam Safety: Ground CoverThe establishment and control of proper vegetationare an important part of dam maintenance. Properlymaintained vegetation can help prevent erosionof embankment and earth channel surfaces, and aidin the control of groundhogs and muskrats. The uncontrolledgrowth of vegetation can damage embankmentsand concrete structures and make close inspection difficult.Grass vegetation is an effective and inexpensive way toprevent erosion of embankment surfaces. If properlymaintained, it also enhances the appearance of the damand provides a surface that can be easily inspected. Rootsand stems tend to trap fine sand and soil particles,forming an erosion-resistant layer once the plants arewell established. Grass vegetation may not be effectivein areas of concentrated runoff, such as at the contact ofthe embankment and abutments, or in areas subjected towave action.Common ProblemsBare AreasBare areas on an embankment are void of protectivecover (e.g. grass, asphalt, riprap etc.). They are moresusceptible to erosion which can lead to localized stabilityproblems such as small slides and sloughs. Bare areasmust be repaired by establishing a proper grass cover orby installing other protective cover. If using grass, thetopsoil must be prepared with fertilizer and then scarifiedbefore sowing seed. Types of grass vegetation that havebeen used on dams in Ohio are bluegrass, fescue, ryegrass,alfalfa, clover, and redtop. One suggested seed mixtureis 30% Kentucky Bluegrass, 60% Kentucky 31 Fescue,and 10% Perennial Ryegrass. Once the seed is sown, thearea should be mulched and watered regularly.ErosionEmbankment slopes are normally designed and constructedso that the surface drainage will be spread out ina thin layer as “sheet flow” over the grass cover. Whenthe sod is in poor condition or flow is concentrated at oneor more locations, the resulting erosion will leave rillsand gullies in the embankment slope. The erosion willcause loss of material and make maintenance of theembankment difficult. Prompt repair of the erosion isrequired to prevent more serious damage to the embankment.If erosion gullies are extensive, a registered professionalengineer may be required to design a more rigidrepair such as riprap or concrete. Minor rills and gulliescan be repaired by filling them with compacted cohesivematerial. Topsoil should be a minimum of 4 inches deep.The area should then be seeded and mulched. Not onlyshould the eroded areas be repaired, but the cause of theerosion should be addressed to prevent a continuedmaintenance problem.FootpathsPaths from animal and pedestrian traffic are problemscommon to many embankments. If a path has becomeestablished, vegetation in this area will not provideadequate protection and a more durable cover will berequired unless the traffic is eliminated. Gravel, asphalt,and concrete have been used effectively to cover footpaths.Embedding railroad ties or other treated woodbeams into an embankment slope to form steps is one ofthe most successful and inexpensive methods used toprovide a protected pathway.Vehicle RutsVehicle ruts can also be a problem on the embankment.Vehicular traffic on the dam should be discouragedespecially during wet conditions except when necessary.Water collected in ruts may cause localized saturation,thereby weakening the embankment. Vehicles can alsoseverely damage the vegetation on embankments. Wornareas could lead to erosion and more serious problems.Ruts that develop in the crest should be repaired bygrading to direct all surface drainage into the impoundment.Bare and eroded areas should be repaired using themethods mentioned in the above sections. Constructedbarriers such as fences and gates are effective ways tolimit access of vehicles.Improper VegetationCrown vetch, a perennial plant with small pink flowers,has been used on some dams in Ohio but is not recommended(see Figure 1). It hides the embankment surface,preventing early detection of cracks and erosion. It is noteffective in preventing erosion.Continued on back!


MaintenanceEmbankments, areas adjacent to spillway structures, vegetatedchannels, and other areas associated with a damrequire continual maintenance of the vegetal cover. Removalof improper vegetation is necessary for the proper maintenanceof a dam, dike or levee. All embankment slopes andvegetated earth spillways should be mowed at least twice ayear. Reasons for proper maintenance of the vegetal coverinclude unobstructed viewing during inspection, maintenanceof a non-erodible surface, discouragement of burrowinganimal habitation, and aesthetics.Common methods for control of vegetation include the useof weed trimmers or power brush-cutters and mowers. Chemicalspraying to kill small trees and brush is acceptable ifprecautions are taken to protect the local environment. Somechemical spraying may require proper training prior toapplication. Additional information can be found on theTrees and Brush Fact Sheet.Figure 1: Crown Vetch(Source: http://www.vg.com)Vines and woody vegetation such as trees and brushalso hide the embankment surface preventing early detectionof cracks and erosion. Tall vegetation also providesa habitat for burrowing animals. All impropervegetation must be removed from the entire embankmentsurface. Any residual roots that are larger than 3 inchesin diameter must be removed. All roots should be removeddown to a depth of at least 6 inches and replacedwith a compacted clay material; then 4 inches of topsoilshould be placed on the disturbed areas of the slope.Finally, these areas must be seeded and mulched toestablish a proper grass cover.Any other questions, comments concerns, or fact sheetrequests, should be directed to the Division of Water at thefollowing address:Ohio Department of Natural ResourcesDivision of WaterDam Safety Engineering Program1939 Fountain Square, Building E-3Columbus, Ohio 43224-1336(614) 265-6731 (Voice) (614) 447-9503 (Fax)http://www.dnr.state.oh.us/odnr/water/Bob Taft Governor • Samuel W. Speck Director • James R. Morris, P.E. ChiefI 07/08/99

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