EFFECTS OF SIMULATED CANOPY COVER AND ANIMAL DISTURBANCES ON RILL AND INTERRILL EROSION1

ABSTRACT: A rainfall simulator was used on runoff plots to study the effects of simulated canopy cover, trampling disturbance, and soil type on nil and interrill erosion. Sandy loam soil was more erodible than clay loam soil. Furthermore, the simulated canopy cover signffi-Soilfactorsrelatedtonil cantly influenced nil and interrill erosion. The effect of trampling on rill and interrill erosion varied with soil type (clay loam versus sandy loam) and erosion type (nh versus interrill erosion). On large plots, where both nil and internill erosion were involved, 30 percent trampling significantly increased soil loss. However, on small plots, 30 percent trampling significantly reduced interrill erosion.     

CHANGES TO INFILTRATION AND INTERRILL EROSION FROM LONG-TERM PRESCRIBED BURNING IN LOUISIANA1

ABSTRACT: Effects of long-term prescribed burning on infiltration and interrill erosion were assessed on two longleaf pine-bluestem sites in Louisiana. Treatments represented biennially-applied winter, spring, or summer burning on an upland sandy loam site for 20 years; and annual winter or spring, and biennial winter or spring burns on a bottomland silt loam site for 10 years, with unburned controls. Immediate effects of burning were a reduction in surface cover, exposing soil to raindrop impact. Burning the sandy loam site increased interrill erosion after winter and spring treatments, but produced no immediate changes in infiltration capacity or time to runoff irrespective of treatment season. Rapid recovery of under-story vegetation mitigated soil exposure. Biennial burning did not increase interrill erosion, or reduce infiltration capacity and time to runoff on the sandy loam site after 20 years. A complete herbaceous understory covered the silt loam site two years after treatment. Interrill erosion was not significantly increased, or infiltration capacity and time to runoff decreased on burning treatments than unburned controls on the silt loam site. Litter biomass was important in predicting interrill erosion. No surface cover condition could be linked to variability in infiltration capacity. This study provides evidence for the resiliency of a longleaf pine-bluestem association to prescribed burning.     

FORMAL EDUCATION IN WILDLAND HYDROLOGY AND WATERSHED MANAGEMENT IN NORTH AMERICA1

ABSTRACT: A survey was made to determine the status of formal education in wildland hydrology by colleges and universities in the United States, Canada, and Mexico. As of December 1977 nine institutions offered the B.S. degree, 18 the M.S. degree, and 17 the degree of Ph.D. with a major or minor in watershed management, forest hydrology, or range hydrology. In addition, 8 other schools offer a minor in watershed management. The survey indicated 44 schools in the United States offer a total of 157 courses, five schools in Canada offer 24 courses, and 1 in Mexico offers one course in the related areas. The survey illustrated rapid growth in education programs and it is anticipated that growth will continue.     

A CASE STUDY OF SHALLOW FLOW PATHS IN A STEEP ZERO-ORDER BASIN1

ABSTRACT: Soil water potentials, slope throughflow, runoff chemistry, and isotopic composition were monitored in a 97 m² zero-order basin within the Maimai 8 watershed on the South Island of New Zealand, for a natural rain storm and two artificial water applications. Contrary to results previously reported for other portions of the Maimai catchment, much of the runoff occurred as a shallow subsurface organic layer flow. For the 47 mm natural rain event, pre-storm soil matric potential ranged from ?60 to ?150 cm H₂O. No saturation was produced within the profile, and the majority of storm runoff emanated from flow within the organic horizon perched on the mineral soil surface. Hillslope applications corroborated this interpretation by showing >90 percent new water flushing with negligible mineral soil moisture response. Although the mechanisms cited in the text are not representative of the entire catchment, the study demonstrates: (1) the value of a combined physical-chemical-isotopic approach in quantifying slope processes, and (2) the heterogeneous nature and diversity of slope runoff pathways in a relatively homogeneous catchment.     

APPLICATION OF SELECTED SOIL LOSS EQUATIONS TO TRAMPLED SOIL CONDITIONS1

ABSTRACT: Soil loss prediction equations (Universal Soil Loss Equation, Modified Universal Soil Loss Equation, and Onstad-Foster Method) were modified to reflect the impact of trampling on soil erosion. The erosion control practice factor, P, was replaced by a trampling ratio, Tr, which is a function of the change in soil erosion due to animal trampling. Trampling impact on soil erosion varied With soil type. The data are a preliminary attempt to account for the impact of trampling on soil erosion.     

Reclaimed Mineland Curve Number Response to Temporal Distribution of Rainfall1

Warner, Richard C., Carmen T. Agouridis, Page T. Vingralek, and Alex W. Fogle, 2010. Reclaimed Mineland Curve Number Response to Temporal Distribution of Rainfall. Journal of the American Water Resources Association (JAWRA) 46(4): 724-732. DOI: 10.1111/j.1752-1688.2010.00444.x Abstract: The curve number (CN) method is a common technique to estimate runoff volume, and it is widely used in coal mining operations such as those in the Appalachian region of Kentucky. However, very little CN data are available for watersheds disturbed by surface mining and then reclaimed using traditional techniques. Furthermore, as the CN method does not readily account for variations in infiltration rates due to varying rainfall distributions, the selection of a single CN value to encompass all temporal rainfall distributions could lead engineers to substantially under- or over-size water detention structures used in mining operations or other land uses such as development. Using rainfall and runoff data from a surface coal mine located in the Cumberland Plateau of eastern Kentucky, CNs were computed for conventionally reclaimed lands. The effects of temporal rainfall distributions on CNs was also examined by classifying storms as intense, steady, multi-interval intense, or multi-interval steady. Results indicate that CNs for such reclaimed lands ranged from 62 to 94 with a mean value of 85. Temporal rainfall distributions were also shown to significantly affect CN values with intense storms having significantly higher CNs than multi-interval storms. These results indicate that a period of recovery is present between rainfall bursts of a multi-interval storm that allows depressional storage and infiltration rates to rebound.     

TEMPORAL AND GEOMORPHIC VARIATIONS OF STREAM STABILITY AND MORPHOLOGY: MAHOGANY CREEK,NEVADA1

ABSTRACT: Detailed studies of long-term management impacts on rangeland streams are few because of the cost of obtaining detailed data replicated in time. This study uses government agency aquatic habitat, stream morphologic, and ocular stability data to assess land management impacts over four years on three stream reaches of an important rangeland watershed in northwestern Nevada. Aquatic habitat improved as riparian vegetation reestablished itself with decreased and better controlled livestock grazing. However, sediment from livestock disturbances and road crossings and very low stream flows limited the rate of change. Stream type limited the change of pool variables and width/depth ratio, which are linked to gradient and entrenchment. Coarse woody debris removal due to previous management limited pool recovery. Various critical-element ocular stability estimates represented changes with time and differences among reaches very well. Ocular stability variables tracked the quantitative habitat and morphologic variables well enough to recommend that ocular surveys be used to monitor changes with time between more intensive aquatic surveys.     

WATER TABLE INDUCED SHRUB-HERBACEOUS ECOTONE: HYDROLOGIC MANAGEMENT IMPLICATIONS1

ABSTRACT: Environmental factors were investigated across a shrub-herbaceous ecotone (sharp zone of change) on a sloping site underlain by shallow groundwater on the arid floor of Owens Valley, California. Dominant plant species were salt rabbitbrush (Chrysothamnus nauseosus ssp. consimilis [E. Greene] Hall and Clements) and saltgrass (Distichlis spicata var. stricta EL.] E. Greene); typical of many similar habitats across the Great Basin. Historic air photographs were analyzed, and soil properties, water table levels and shrub and herbaceous cover were measured at discrete sample points. To investigate soil and vegetation spatial properties, sample points were apportioned on both sides of the ecotone. Land management practices and fire were ruled out as causal factors for the ecotone which remained stable through a 45-year period of air photo record. Soil textural, chemical and hydraulic properties were similar across the ecotone and were uniform throughout the site. Only depth to the water table changed significantly in a gradient perpendicular to the ecotone. The shrub-herbaceous ecotone was located where the water table depth fluctuated periodically between 0.8 and 1.2 m; deeper water tables than this range favors shrub cover while shallower depths favors meadow vegetation. When extrapolated to hydrologic management such as groundwater pumping, such a shallow depth and a narrow range of amplitude could restrict options for water development if maintenance of meadow vegetation is a goal.     

UPLAND SOIL EROSION SIMULATION FOR AGRICULTURAL WATERSHEDS1

ABSTRACT: A soil erosion simulation model that considered the physical conditions of agricultural watersheds and that interfaced with the modified USDAHL-74 watershed hydrology model was developed. The erosion model simulates the detachment and transport of soil particles caused by raindrop impact and overland flow from rill and interrill areas. The model considers temporal and spatial variation of plant residue, crop canopy cover, snow cover, and the moisture content of surface soil as modifying factors of the erosive forces of raindrop impact and overland flow. The hydrology model simulates overland flow and some of the physical parameters that are used in the erosion model. The simulation is executed in the time interval determined by the rainfall rate or snowmelt rate. The erosion model compares the transport capacity of the overland flow and the sediment loaded in the overland flow to determine the fate account for the free soil particles that have already been detached and are readily available to be transported by the overland flow. The model was tested with data from two small agricultural watersheds in the Palouse region of the Pacific Northwest dryland. The model was calibrated by trial-and-error to determine the coefficients of the model.     

RUNOFF AND SEDIMENT YIELD UNDER GRAZING IN FOOTHILLS FESCUE GRASSLANDS OF ALBERTA1

ABSTRACT: Grazing can have a profound impact on infiltration and thus runoff and erosion. The objectives of this study were to quantify the effects of select grazing systems on rainfall and snowmelt induced runoff and sediment yield from sloped areas of the foothills fescue grasslands of Alberta, Canada. The effects of two grazing intensities (heavy and very heavy) for two durations (short duration and continuous throughout the growing season) were compared to an ungrazed control between June 1988 and April 1991. Runoff was measured using 1-rn² runoff frames and collection bucket systems. Sediment yields were then determined on samples from the collected runoff. Snowmelt was the dominant source of runoff. Snowmelt runoff was higher from the heavily grazed areas than from the very heavily grazed areas, due to the higher standing vegetation which accumulated snow in the former areas. Sediment yields as a result of snowmelt were generally low in all areas. Only a few summer storms caused runoff. Runoff volumes and sediment yields from summer rainstorms were low, due to low rainfall and to generally dry antecedent soil moisture conditions. The greatest risk of summer runoff, and thus sediment yield, appears to occur in August.     

A DISTRIBUTED DYNAMIC WATERSHED MODEL1

ABSTRACT: A distributed watershed model was developed to mathematically simulate overland and channel flow for a single-event storm. The modeled watersheds in the study were subdivided into rectangular grid elements. All hydrologically significant parameters, such as land slope, rainfall and precipitation excess, were assumed to be uniform within each element. The Green-Ampt method was adopted to generate precipitation excess for each element during the simulation period. A two-dimensional diffusion wave model was used for overland flow routing and an iterative Alternative Direction Implicit scheme was used to solve the simultaneous overland flow equations. Once the overland flow became inflow to the channel, a one-dimensional dynamic wave flood routing technique, based on a four-point, implicit, non-linear finite difference solution of the St. Venant equation of unsteady flow, was applied. A limited number of comparisons were made between simulated and observed hydrographs for areas of about one square mile. Given the appropriate parameters, the model was able to accurately simulate runoff for single-event storms. This paper describes a distributed watershed model developed to simulate overland and channel flow. Comparisons were made between simulated and observed hydrographs for three watersheds. The model was able to accurately simulate the runoff for single-event storms using 61-m by 61-m (200 ft by 200 ft) watershed grid elements.     

Peak Runoff Model Comparison on Central Illinois Watersheds1

ABSTRACT: Four peak runoff rate models were tested with 183 gage years of record to determine the model most applicable to small watersheds of mild topography in east-central Illinois. The Cypress Creek, Rational, Chow, and SCS peak runoff models were evaluated for their performance. Statistical analyses indicated the Soil Conservation Service model was most appropriate for the watersheds tested.     

URBANIZATION,FLOOD FREQUENCY,AND SALMON ABUNDANCE IN PUGET LOWLAND STREAMS1

ABSTRACT: Urbanization history and flood frequencies were determined in six low-order streams in the Puget Lowlands, Washington, for the period between the 1940150s and the 1980190s. Using discharge records from USGS gauging stations, each basin was separated into periods prior to and after urban expansion. Four of the study basins exhibited significant changes in urbanized area, whereas two of the study basins exhibited only limited change in urbanized area and effectively serve as control basins. Each of the basins that experienced a significant increase in urbanized area exhibited increased flood frequency; pre-urbanization 10-year recurrence interval discharges correspond to 1 to 4-year recurrence interval events in post-urbanization records. In contrast, no discernible shift in flood frequency was observed in either of the control basins. Spawner survey data available for three of the study basins reveal systematic declines in salmon abundance in two urbanizing basins and no evidence for decreases in a control basin. These data imply a link between ongoing salmon population declines and either increased flood frequency or associated changes in habitat structure.     

MODEL PREDICTIONS OF WATERSHED HYDROLOGIC COMPONENTS: COMPARISON AND VERIFICATIION1

ABSTRACT: Model predictions of the relatively simple soil compartment model SESOIL are compared with those of the more data-intensive terrestrial ecosystem hydrology model AGTEHM. Comparisons were performed using data from a deciduous forest stand watershed, a grassland watershed, and two agricultural field plots. Good agreement was obtained between model predictions for annual values of infiltration, evapotranspiration, surface runoff, and groundwater runoff. SESOIL model predictions also compare well with empirical measurements at the forest stand and the grassland watersheds.     

A COMPARISON OF METHODS OF ESTIMATING MEAN WATERSHED SLOPE1

ABSTRACT: Ten topographic analysis methods were employed to estimate watershed mean slopes for 13 small forested watersheds (32 to 131 mi²) in East Texas. Of the ten methods employed, the mean slope curve is the most accurate but also the most tedious and laborious one. The method can be simplified by measuring only the lengths of five contours and the areas between these contours within the watershed with little loss of its accuracy. Watershed slopes estimated by the contour length method, the grid contour method, the systematic slope sampling method, and the simplified contour length method are satisfactory for general purposes and relatively simple. The watershed circumference-stream length method, the length-width axis method, the Justin method, and the regression plane method are not suitable for estimating watershed slopes in East Texas without modification.     

Modeling of Sediment Yield From Anjeni-Gauged Watershed,Ethiopia Using SWAT Model1

Setegn, Shimelis G., Bijan Dargahi, Ragahavan Srinivasan, and Assefa M. Melesse, 2010. Modeling of Sediment Yield From Anjeni-Gauged Watershed, Ethiopia Using SWAT Model. Journal of the American Water Resources Association (JAWRA) 46(3):514-526. DOI: 10.1111/j.1752-1688.2010.00431.x Abstract: The Soil and Water Assessment Tool (SWAT) was tested for prediction of sediment yield in Anjeni-gauged watershed, Ethiopia. Soil erosion and land degradation is a major problem on the Ethiopian highlands. The objectives of this study were to evaluate the performance and applicability of SWAT model in predicting monthly sediment yield and assess the impacts of subbasin delineation and slope discretization on the prediction of sediment yield. Ten years monthly meteorological, flow and sediment data were used for model calibration and validation. The annual average measured sediment yield was 24.6 tonnes/ha. The annual average simulated sediment yield was 27.8 and 29.5 tones/ha for calibration and validation periods, respectively. The study found that the observed values showed good agreement with the simulated sediment yield with Nash-Sutcliffe efficiency (NSE) = 0.81, percent bias (PBIAS) = 28%, RMSE-observations standard deviation ratio (RSR) = 0.23, and coefficient of determination (R²) = 0.86 for calibration and NSE = 0.79, PBIAS = 30%, RSR = 0.29, and R² = 0.84 for validation periods. The model can be used for further analysis of different management scenarios that could help different stakeholders to plan and implement appropriate soil and water conservation strategies.