Conservation Terraces Used Terraces when conservation practices cannot reduce erosion to tolerable level Bench terraces Old means of controlling runoff and erosion Used in countries with large populations and limited areas of arable land 1 Graded Terraces Used in areas with a commercialtype agriculture where machinery is available and labor costs are high A graded terrace consists of a channel with a ridge on the downhill side The channel slopes gently toward a protected outlet Graded Terraces They reduce erosion because they shorten slope lengths and thereby reduce runoff volume and velocity Parallel and steep backslope terraces are modification that make farming terraced fields easier Terraces need proper care to maintain adequate channel capacity and must be repaired when storms cause major damage Diversions Diversions serve many purposes ranging from diverting runoff water away from a gully or around a cultivated field to carrying runoff to ponds and storage reservoirs The diversion channel is usually a high capacity grass waterway and is seldom cropped Diversions Diversions and non level terraces must have protected outlets Grass waterways are common but underground pipe outlets are becoming more popular Erosion can occur in the beds of vegetated waterways Structures needed to control erosion may either be temporary or longterm 2 Temporary Structures Used to control erosion in waterways and gullies while perennial vegetation or other permanent control is being established Temporary structures include artificial mulch in shaped and seeded small grain waterways and barriers in channels Temporary Structures Artificial mulch may consist of burlap or special prepared cloth paper plastic or shredded wood mats Barriers may be made of rock wood or brick Barriers must make firm contact with floor and walls of waterway or gully so water cannot wash under or around 3 Concrete Drop Structures Drop structures and chutes are permanent control devices used where vegetation is impractical Drop structures and chutes have three critical parts Inlet Outlet Aprons water fall onto and is spread at lower level Temporary Structures Current deflectors bank protectors and floodways have been used with varying success to control streambank erosion Concrete Drop Structures Several types of storage dams are used in soil and water conservation activities To trap sediment Stabilize a gully or a channel grade Store runoff temporarily to reduce flooding soil loss and sedimentation Temporary Structures Wind erosion control structures Woven mat barriers Dune leveling Snow fences U S Army Corps of Engineers must okay as well as the state 4 5 6 7 Terrace System in Illinois What are terraces Terraces are earth embankments channels or combinations of embankments and channels constructed across a field slope Shorten length of slope How much do terraces cost Cot of terraces 2500 farm year now 3500 farm year Piatt County Cost of outlets underground or grassed waterway types ASCS Agricultural Stabilization and Conservation Service provide incentive payments to offset some of your terrace constructions costs Where can I go for assistance Develop an overall plan determine proper type and spacing of terraces and type of outlet system Soil and Water Conservation District County Extension advisor Directory of Illinois Land Improvement Contractors Association competent contractors who have had experience in your county What are purposes of terraces Control erosion Manage runoff Convenient to farm Allow broader range of plant choices and more intense use of row crops How much do terraces cost ASCS Agricultural Stabilization and Conservation Service provide incentive payments to offset some of your terrace constructions costs Illinois Land contractors 8400 feet of terraces 2400 feet of waterways How do soil type and field slope influence decisions about terraces Save topsoil and place over construction area if it is thin to start with Narrow base system best when subsoils exposed less disturbance Broad base terraces are best used most effective on long uniform gentle slopes up to 5 to 6 Grass back terraces on slopes of 6 to 15 consider these terraces grass can stabilize slopes 8 What kinds of terraces are used Gradient terrace with a grassed waterway outlet Gradient terraces with underground outlets or parallel tile outlet PTO terraces Promotes parallel alignment Reduces need for grassed waterways more effective and more farmable Shape of ridges in cross section Broad base low slope gradients Grass back slope higher slope gradients Narrow base Reduces amount of earth moved Entire ridge is grassed Smaller area of farm removed from productivity 9 How effect are terraces in controlling sheet and rill Erosion as compared to other conservation practices More effective Can I install the entire terrace system at one time Yes but Will the inlet pipes for underground outlets be an obstruction to my equipment Distance between ridge and intake rise 1 to 2 multiple of equipment Narrow base terraces place inlet close to grassed ridge Put inlet on a short branch off main line in case struck by snow mobile or equipment What must I do to maintain the terraces Channel capacity must be maintained danger of over topping Sediment deposited near the intake needs to be removed during tillage to keep it the low point Cost ASCS Need to clean and repair intakes after each storm or repair promptly any farm machinery damage to outlet Will the cross sections of terraces be dangerous to farm Grass backed slope Steep part not farmed Have been some tractor accidents Are all terraces difficult to farm Not if planned designed and constructed properly Terraces should Be parallel whenever possible few point rows Be parallel or perpendicular to field boundaries Have gentle circular turns with minimum curvature 10 What must I do to maintain the terraces Rodent holes in terrace ridges can be a problem especially in grassed ridges Inspect and repair regularly Grassed terrace slopes should be moved periodically and growth of brush controlled to avoid attracting rodents How do soil type and field slope influence decisions about terraces If farm s topsoil is shallow with short irregular slope should not install terraces Conversion to perennial vegetation Conservation tillage When should terraces be used with other erosion reducing practices Long slopes terraces manage water as well as soil Terrace system can divert water away from gully Are all terraces difficult