Controlling Channel InstabilityDesign criteria for channel erosion control structures developed:
Procedures developed for predicting streambank erosion:
- Procedures for design of low drop channel grade control structures were determined from physical models and refined through field demonstrations. These structures have or will be constructed at a total of 137 sites in DEC watersheds alone, and at numerous other sites throughout the nation. They are economical, the design and layout time is minimal, only a short construction period is required preventing need for streamflow diversion, and dewatering can normally be accomplished with sump pump. The rock lined stilling basin provides excellent aquatic habitat. Installation of these structures has prevented massive erosion of channels and millions of dollars of damage to roads, bridges and other riparian structures.
Methods tested for controlling severe bank erosion with combinations of vegetation and structure:
- Procedures were developed to predict whether or not stream banks would collapse based on soil properties, bank height, and bank angle. These analyses are widely used by engineers worldwide seeking to control streambank erosion.
Estimating the effects of woody debris removal on channel flow capacity:
- Streambank erosion controls involving vegetation are in great demand because of economic and environmental considerations. Relatively little design guidance is available. Field tests were conducted at eleven sites along 7 streams. Monitoring continued for up to 10 years, and casual observation for up to 18 years. Woody and nonwoody species best suited for streambank applications were identified, as were the best types of structure to use with vegetation.
Unstable stream restoration criteria developed:
- Fallen trees and logs are important components of stream ecosystems. These objects are often removed to control flooding and erosion, but prediction of the effects of debris removal on flow capacity is imprecise. A simple technique for predicting the capacity of river channels with varying amounts of woody debris was developed. Engineers can use this procedure to analyze benefits of selective debris removal proposals and weigh benefits against likely environmental impacts.
- Engineering problems that must be addressed to restore stream corridors in agricultural landscapes are complex and little information in the literature is applicable to unstable, warmwater streams. A series of stream restoration experiments has been conducted to fill major knowledge gaps. Ecological health of two incised streams were restored by adding small stone structures and willow cuttings. Physical and biological responses were positive, but varied from site to site. Data sets, which have provided a basis for a national handbook, a textbook, and more than 20 other publications, are still being analyzed. Existing publications are frequently requested by engineers and scientists working on stream restoration projects across the US and in other countries.
Analysis of water quality of drop pipe inlet basins:
Agricultural contaminants in mixed agricultural watersheds:
- Drop pipe inlets are erosion control structures used extensively along eroding stream channels. For example, 2,568 of these devices will be installed as part of the DEC. Common to many of these structures are shallow pools. Preliminary data indicate that these erosion control structures also improve stream water quality by processing nutrients from storm run-off and trapping suspended sediments before they reach the stream. Ongoing studies will facilitate extension and quantification of these benefits to agricultural watersheds in other regions.
Small impoundments for reducing offsite agricultural pollution:
- A comprehensive study of contamination of water, soil, sediment, and animal tissue by pesticides and metals in a mixed cover agricultural watersheds showed that metals were concentrated in sediments while pesticides bioaccumulated in fish. This evidence indicates that erosion control techniques developed by the DEC program may therefore reduce pesticide contamination by controlling erosion and sediment transport .
Test developed to screen contaminated sediments for toxicity:
- Farm ponds similar were shown to be efficient measures to reduce offsite pollution from agriculture. During a long term study, an average of more than 70% of suspended sediment, phosphorus, and nitrogen flushed into the pond was retained instead of passing into adjacent streams. This information has spurred application of small impoundments for nonpoint source pollution control.
- A microbiological-based bioassay for sediments was developed to provide rapid screening of stream sediments for acute, high levels of toxic contamination. Application will provide enhanced environmental protection at reduced cost.
EcologyVertebrate habitats created by drop pipes:
Environmental evaluations of watersheds:
- Drop pipes are a common method of controlling gully erosion. These structures convey runoff from field level to stream level through a metal pipe. Pipe inlets allow small terrestrial and wetland habitats to develop. Habitat values have been quantified by field sampling fish, birds, reptiles, and amphibians. Landowners and resource managers with State and federal agencies can use this information to enhance stream corridor environments at no extra cost when repairing gullies.
IBI tested in unstable, warmwater streams:
- Samples of fish, invertebrates, physical habitat parameters, and water quality were collected at 38 sites in 15 DEC watersheds. Resulting data were used to construct a database useful for evaluation of watershed management projects through out the country.
Habitat recovery in incised, channelized streams is facilitated by construction of grade control structures:
- In the last ten years, indices of biotic integrity (IBI) have been widely used to measure environmental quality of stream ecosystems. However, relatively little use has been reported for Southeastern coastal plain streams. Indices of biotic integrity (IBI) were computed using fish samples from 27 locations in the DEC watersheds. This effort showed that regional application of the IBI was not an efficient evaluation tool due to high temporal variability, lack of reference streams and low sample size. This finding will prevent misapplication of a popular technology and inefficient use of funds for environmental monitoring.
Ecological value of channel erosion control structures quantified:
- Fish populations occurring in pools below grade control (low-drop) structures and naturally occurring pools were compared. Structures provided habitats equal or superior to natural pools in these unstable streams showing that grade control structures, such as the 137 constructed for the DEC project, offer protection from stream channel degradation while providing additional habitat diversity. These findings may be used to rehabilitate damaged streams nationwide.
- The value of erosion control stone (riprap) as stream insect habitat was determined by sampling macroinvertebrates from gravel, sand, woody debris, and riprap in three streams. Riprap, though representing less than 5% of available substrate, harbored more types of invertebrates than either sand or gravel which made up 90% of available substrate. Though riprap supported a low average population density, it was very similar to naturally occurring woody debris in supporting a diverse assemblage of invertebrates. The effect of riprap structures on invertebrates and fish occurring in small streams and large rivers was assessed using DEC-derived data and a literature review. The results may be used to plan and design river control projects at a variety of scales and regional settings.
New Upland Erosion Control PracticesAgricultural Management Systems to Reduce Sediment Production:
No-till economically attractive:
- Includes development of conservation systems for cotton, soybean, corn and wheat; evaluation of runoff, erosion, and water quality from plots and small watersheds farmed with a wide range of cropping systems; and numerous supporting projects. This project has provided information vital to row crop producers in the region who must remain profitable and also meet soil loss limits mandated by the Food Security Act. Hundreds of producers, consultants, reporters, action agency, and industry representatives have requested information, visited the experimental farm, and attended field days. These studies have been the subject of a commercial video presentation and several feature articles.
No-till reduces runoff and erosion:
- No-till cotton, corn, soybean and sorghum have been higher yielding and produced greater profits than conventional tillage management on fragile upland silt loam soils. These controlled studies led to several ongoing field-scale on-farm trials and contributed to the recent increase in the fraction of cropland in the region and nationally that is planted no-till.
Legume cover crops with superior reseeding characteristics identified:
- Compared to conventional tillage, planting no-till following a cover crop reduced runoff from upland plots from 27% of rainfall to as low as 8%. Over a five-year period, no-till planting reduced annual sediment yield from upland watersheds from 13 tons/a to 0.3 tons/a.
Stiff-grass hedges are low-cost biological sediment control structures:
- Non-traditional cover crops were screened at 12 locations in 6 states (AL, AR, GA, LA, MS, TN) to identify varieties with superior combinations of winter hardiness, early maturity, and hard seededness so that they will come back for several years from a single seed crop. Self-reseeding will increase cover-crop use by farmers who cannot plant them every year.
- Grass hedges are narrow (~3 ft wide) strips of stiff, erect, dense grass that can retard wind and surface runoff waters, causing deposition of eroded sediment and preventing blowing sand from damaging young crops. Hedges can be established at a seed cost of only $0.01/ft. Plot studies found that established hedges trap 80% of sediment from upland cotton cropland. Detailed flume studies determined even where runoff of 1inch/hr from one acre is concentrated into a flow area only 1 ft wide, hedges can trap 90% of sand-sized sediment and 20% of even very fine sediment. Based on these research findings and those of colleagues, a set of interim national standards entitled "Vegetative barriers for runoff and sediment control" was drafted and submitted to the USDA-NRCS. These standards were distributed nationally by NRCS and are being used in several states (HI, IA, MS, MO, NJ, PR, SC, VA) as the basis for field evaluations of this technology.
Erosion Processes InformationNo-Till Soil Loss Reduction Much More than Previously Thought:
Lower Erosivity Values for Mid-South:
- No-till is much more effective at reducing soil loss than had previously been credited in the Universal Soil Loss Equation. The relationships derived from this analysis have been incorporated into RUSLE, the Revised Universal Soil Loss Equation which is used National for assessing compliance with national legislation.
Improved Analysis Techniques of Watershed Systems:
- Research showed that regional coefficients used in RUSLE for the Mid-South underestimate erosion by as much as 30%. Integration of these findings into RUSLE will reduce erosion from southern farmland.
- Software has been developed that allows a complete systems analysis approach to watershed management. Linking watershed process interactions together in a comprehensive watershed modeling package enables improved designs of erosion control structures. Long term simulation studies performed on the DEC watersheds demonstrated the applicability of the model to watershed management. This software is required by action agency personnel to effectively develop watershed management plans.
Fundamental Information on Sediment TransportImproved Management of Watersheds from Research Database:
- Data collected on the Goodwin Creek Watershed encompasses all of the main processes that govern the movement of sediment and water through the watershed. Watershed management throughout the world has been improved through the use of this database for the development and testing of watershed models. Informed management of watersheds is critical for efficient and sustainable use of watershed resources. The variability of the processes documented in this project indicate the need to collect data over a long period of time.