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Runoff Estimation, and Surface Erosion and Control

Runoff Estimation, and Surface Erosion and Control

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Runoff Estimation, and Surface Erosion and Control

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  1. Runoff Estimation, and Surface Erosion and Control Ali Fares, PhD NREM 600, Evaluation of Natural Resources Management

  2. What’s soil erosion? Erosion is the process of detachment and transport of soil particles by erosive agents (Ellison, 1944) Erosion is a natural geologic process • WATER EROSION • WIND EROSION • TILLAGE TRANSLOCATION

  3. SOIL EROSION IS GLOBAL PROBLEM • 1/3 WORLD’S ARABLE LAND LOST SINCE 1950 • MOST IN ASIA, AFRICA, S. AMERICA • 13-18 t/a/yr • 30% OF US FARMLAND ABANDONED • EROSION • SALINIZATION • WATER-LOGGING • 90% OF US CROPLAND LOSING SOIL FASTER THAN IT IS REPLACED • >1 t/a/yr

  4. SIGNIFICANT SOIL LOSS IN THE USA WATER 3.5 X 109 T/yr WIND 1.5 X 109 T/yr

  5. WIND EROSION SUSPENSION WIND SALTATION CREEP • SALTATION DETACHES PARTICLES • SMALLER PARTICLES SUSPENDED • LARGER PARTICLES CREEP • SANDY AND SILTY SOILS MOST SUSCEPTIBLE • SOIL ACCUMULATION IN DITCHES AND FENCE ROWS

  6. WIND EROSION CAN BE SIGNIFICANT Near Mitchell, SD

  7. Dust bowl • 1931-1939 there was a drought called the “dust bowl”. It caused huge dust storms to erupt that destructed billions of acres of farm land.

  8. storms • In the first year of the drought there were 14 storms reported and the second year there were 38 storms. It was getting worse.

  9. Ruined land • Tons of damage was done to every ones land and it costs billions of dollars to repair the damages.

  10. Black Sunday • April 14th,1934 black Sunday was the worst blizzard of the dustbowl which caused the most extensive damage.

  11. REDUCING WIND EROSION • MAINTAIN SURFACE COVER • CROP RESIDUE • COVER CROPS • INCREASE STUBBLE HEIGHT • INSTALL WINDBREAKS • EFFECTIVE 15x HEIGHT • IRRIGATE • STRIP CROPS PERPENDICULAR TO PREVAILING WIND

  12. The Shelterbelt Program

  13. WATER EROSION PROCESS • BEGINS WITH RAINDROPS STRIKING BARE SOIL DISLODGING PARTICLES • INTENSE RAINS SEAL SURFACE • WHEN RAINFALL EXCEEDS INFILTRATION WATER IS STORED IN SMALL DEPRESSIONS • ONCE DEPRESSIONS ARE FILLED, RUNOFF BEGINS

  14. WATER EROSION PROCESS • Initially water flows in a discontinuous sheet • Eventually it concentrates into small channels or rills. The runoff now has energy to break off particles and cut deeper • The amount of erosion caused by sheet and rill erosion increases with slope and distance • Rills may eventually form gullies

  15. THE SOIL WATER EROSION PROCESS

  16. EFFECTS ON ENVIRONMENTAL QUALITY AND PRODUCTIVITY • LOSS OF OM, CLAY, AND NUTRIENTS REDUCES PRODUCTIVITY • DAMAGE TO PLANTS • FORMATION OF RILLS AND GULLIES AFFECTS MANAGEMENT • SEDIMENTATION IN WATERWAYS, DIVERSIONS, TERRACES, DITCHES • DELIVERY OF NUTRIENTS TO SURFACE WATER

  17. Quantifying Soil Erosion

  18. Standard USLE plot: • 22.1m (72.6 ft) long • 9% slope • 4m (13.12 ft) wide.

  19. USLEUniversal Soil Loss Equation • Wischmeier, W.H. and D.D. Smith. 1978. Predicting rainfall erosion losses. USDA Agriculture Handbook 537, U.S. Department of Agriculture.

  20. Empirical model: • Analysis of observations • Seeks to characterize response from these data. • Based on: • Rainfall pattern, soil type, topography, crop system and management practices. • Predicts: • Long term average annual rate of erosion • Subroutine in models such as: • SWRRB (Williams, 1975), EPIC (Williams et al., 1980), ANSWERS (Beasly et al., 1980), AGNPS (Young et al., 1989)

  21. The equation: A = R x K x LS x C x P • A = average annual soil loss (tons/acre year) • R = rainfall and runoff erosivity index • K = soil erodibility factor • L = slope length factor • S = slope steepness factor • C= crop/management factor • P = conservation or support practice factor

  22. R (rainfall and runoff erosivity index) • Erosion index (EI) for a given storm: • Product of the kinetic energy of the falling raindrops and its maximum 30 minute intensity. • R factor =EI over a year / 100 A =R x K x LS x C x P

  23. Average annual values of the rainfall erosion index (R).

  24. K(soil erodibility) • Susceptibility of a given soil to erosion by rainfall and runoff. • Depend on: • Texture, structure, organic matter content, and permeability. A =R x K x LS x C x P

  25. Soil-erodibility nomograph.

  26. LS(slope length-gradient) • Ratio of soil loss under given conditions to that at a site with the "standard" slope and slope length. A =R x K x LS x C x P

  27. Topographic LS factor

  28. Crop Tillage Factor Factor Fall Plow Grain Corn 1.00 0.40 Silage Corn, Beans & Canola Spring Plow 0.90 0.50 Cereals (Spring & Winter) Mulch Tillage 0.60 0.35 Seasonal Horticultural Crops Ridge Tillage 0.35 0.50 Fruit Trees Zone Tillage 0.25 0.10 No-Till Hay and Pasture 0.25 0.02 C(crop/management) • Ratio of soil loss from land use under specified conditions to that from continuously fallow and tilled land. A =R x K x LS x C x P

  29.  Support Practice P Factor Up & Down Slope 1.00 Cross Slope 0.75 Contour farming 0.50 Strip cropping, cross slope 0.37 Strip cropping, contour 0.25 P(conservation practices) • Ratio of soil loss by a support practice to that of straight-row farming up and down the slope. A =R x K x LS x C x P

  30. RUSLE: Revised Universal Soil Loss Equation • USDA Agriculture Handbook 703(Renard et. al. 1997) • USLE factor values: updated, expanded, improved. • Expanded isoerodents • Ponded water on the soil • Freeze-thaw cycle and soil moisture • Complex slopes • Conservation tillage and crop rotation • Software

  31. WHAT IS RUSLE 2 • “GREAT GRANDSON” OF USLE • MODEL TO PREDICT SOIL LOSS • WHERE OVERLAND FLOW OCCURS • COMPUTES ANNUAL SHEET/RILL EROSION • COMPUTES PARTICLE DISTRIBUTION AND RUNOFF • CROPLAND, FOREST, LANDFILLS, CONSTRUCTION SITES, SURFACE MINES • WINDOWS “PULL DOWN” MENUS

  32. WHO AND WHAT OF RUSLE 2 • USDA-ARS, USDA-NRCS, VARIOUS UNIVERSITIES • ON-GOING PROCESS OVER 70 YEARS • THOUSANDS OF RESEARCH DATA • SET UP WITH VARYING LEVELS OF COMPLEXITY • COMPUTER REQUIREMENTS • WINDOWS 98 • INTERNET EXPLORER BROWSER • 64 MB RAM • DOWNLOAD • HTTP://BIOENGR.AG.UTK.EDU/RUSLE2/

  33. APPLICABILITY OF RUSLE 2 • ESTIMATES INTER-RILL AND RILL EROSION • ESTIMATES SEDIMENT YIELD FROM OVERLAND FLOW AND TERRACE CHANNELS • DOES NOT ESTIMATE EPHEMERAL OR PERMANENT GULLIES, MASS WASTING, OR STREAM CHANNEL EROSION • BEST SUITED TO CROPLAND, BUT IS USEFUL FOR CONSTRUCTION SITES, LANDFILLS, RECLAMATION PROJECTS, AND DISTURBED FOREST LAND

  34. APPLICABILITY OF RUSLE 2 (cont.) • BEST WHERE RAINFALL IS REGULAR AND EXCEEDS 20”/YR. • MEDIUM-FINE TEXTURED SOILS • SLOPES 3-20% AND LESS THAN 600 FT. • BEST AT CALCULATING “AVERAGE ANNUAL SOIL LOSS”, NOT RECOMMENDED FOR SINGLE STORM EVENTS

  35. RUSLE 2 FACTORS A = R x K x LS x C x P • CLIMATE (R) AND SOIL (K) FACTORS ARE SET FOR A GIVEN FIELD • SLOPE GRADE (S) AND LENGTH (L) CAN BE ADJUSTED WITH DIFFICULTY • MOST FLEXIBILITY WITH COVER MGT. (C) AND SUPPORTING PRACTICES (P)

  36. EROSION CONTROL PRACTICES Structures: diversions, terraces, waterways • Reduce slope length • Slow runoff velocity • Divert excess water safely • Avoid runoff over barnyard, feedlots, etc.

  37. CONTOUR TERRACES Grant Co.

  38. EROSION CONTROL PRACTICES Management practices • Cover crops • Crop residue management • 30% residue reduces erosion 50-60% • Contour tillage • Slope < 8% and 300’ long • Contour strip cropping and buffers • Alternating sod strip for steep land

  39. Controlling Water contaminants at the Source, Kaiaka-Waialua Watershed

  40. Kaiaka and Waialua bays, are water quality limited segments due to high levels of total P, NO-3, chlorophyll a, and turbidity exceeding the maximum allowable levels (HI-DOH). • Sediment loads from agricultural lands and effluent discharged from household cesspools are two of the major sources of pollution. • Sediment losses are generated from cropped and fallow zones as a result of an intensive agricultural system that includes a crop/fallow cropping combination.

  41. Objectives • The goal of this project is to implement and demonstrate erosion control practices to help manage erosion throughout Kaiaka-Waialua watershed, thereby reducing sediment and potential pollutant loads (P, N) into the surface water resources, and consequently improving water quality of the coastal area.

  42. Materials and Methods • Field in a commercial farm, • Ewa Silty clay soil, a mean Ksat = 3.5 cm d-1 (Candler 15 m d-1) • Three cover crops (Sunn hemp, Sudex & Oats) were replicated 3 times in a RCB design. • Suction cups were installed in each plot to collect soil solution • Surface runoff was collect from each plot following rainfall. • Soil water contents (10,20,30 & 50cm) from each treatment

  43. Materials and Methods • Soil physical properties were determined: Ksat, BD & soil water release curve • Soil samples were collected before, in the middle and at the end of the trial. • Total dissolved and total suspend solids (TDS, TSS) were determined (EPA’s 160.1, 160.2 methods) • NO3, NH4 and P were determined by UH-ADSC