EFFECT OF SURFACE MINING ON STORM FLOW AND PEAK FLOW FROM SIX SMALL BASINS IN EASTERN KENTUCKY1

ABSTRACT: Hydrologic records from six small Eastern Kentucky watersheds were analyzed to determine the effect of surface mining on storm flows and peak flows. Average storm flow volumes were not changed by surface mining, whereas average peak flows were increased 36 percent. Peak flow increases were only in the summer. Smaller peak flows are doubled; moderate ones are increased by about a third; peak flows around 100 csm seem to be largely unaffected; and the larger peak flows may have been reduced by surface mining. The maximum annual storm flows, usually in winter or spring, appeared slightly reduced. No time trend in either storm flows or peak flows could be detected in five years of postmining record. Surface mining is not a serious floodwater discharge problem.     

EQUIVALENCE BETWEEN TOPMODEL AND THE NRCS CURVE NUMBER METHOD IN PREDICTING VARIABLE RUNOFF SOURCE AREAS1

An equivalence is proposed between two rainfall‐runoff methods with a long history of use in the United States and Europe. In watersheds where variable source areas dominate runoff, the two methods can have comparable probability distribution functions of moisture deficit, and therefore predict similar saturated runoff source areas. A novel approach is introduced to determine the S parameter in the Natural Resources Conservation Service (NRCS) method. This approach constrains S by the physical soil and topography characteristics of the catchment and depth to water table. The NRCS curve number method is at the core of many rainfall‐runoff models in hydrology. As a simple lumped parameter method, it is often scrutinized because it is not obvious how to derive S from catchment hydromorphological characteristics. The novel approach provides a clear physical meaning for S, allowing better estimation of this parameter in humid shallow water table environments where the variable source area can be the dominant runoff mechanism.     

MODELING RUNOFF FROM VARIABLE SOURCE AREAS IN HUMID,SHALLOW WATER TABLE ENVIRONMENTS1

ABSTRACT: Variable Source Areas (VSAs) are zones with water saturated soils in forested wetlands fringing streams and creeks. Runoff from these areas is generated by saturation excess after a shallow water table rises and inundates the ground surface. In humid regions, like Florida and the Southeast, VSAs are believed to produce most of the runoff in shallow water table environments. Modeling the spatial extent and temporal fluctuation of a VSA is difficult because the formation of a VSA depends on a number of hydrological and morphological factors like rainfall intensity, soil texture, water table depth, and topographic attributes of the terrain. In this paper, we couple a digital elevation model with a two‐dimensional variable saturation model to illustrate the formation of a VSA at the hillside scale. The topography derived from the digital elevation model forms the upper domain geometry for the two‐dimensional finite element simulations of variable saturated flow. The objectives are: (1) to model the spatial and dynamic fluctuation of a VSA, and (2) to understand the roles of rainfall variability and terrain attributes on the formation of a VSA. Results show that hillsides with shallow water table depths, low saturated hydraulic conductivity, mild slopes, and concave slope curvature were more susceptible to runoff from a variable source. Runoff from a variable source showed little sensitivity to rainfall intensity. In general, landscapes with steep slopes generated a small VSA and a seepage face that vanished rapidly with time. In contrast, flat terrains are more amenable to VSA and retain ground surface inundation for longer periods of time.     

A MODIFIED RATIONAL FORMULA FOR FLOOD DESIGN IN SMALL BASINS1

ABSTRACT: New formulas and procedures under the framework of the Rational Formula are presented that are applicable to flood design problems for a small basin if the geometry of the basin can be approximated as an ellipse or a rhombus. Instead of making the assumption in the traditional rational formula that the rainfall is uniformly distributed in the whole duration (D_w) of a design storm, the new method modifies that assumption as: the rainfall is uniformly distributed only in each time interval CD) of the design storm hyetograph, thus extending the rational formula applicable to the case that the rainfall duration is less than the basin concentration time (T_c). The new method can be applied to estimate the flood design peak discharge, and to generate the flood hydrograph simultaneously. The derivation of the formulas is provided in detail in this paper, and an example is also included to illustrate how to apply the new formulas to the flood design problems in small basins.     

SUSPENDED SEDIMENT AND METALS REMOVAL FROM URBAN RUNOFF BY A SMALL LAKE1

ABSTRACT: A small lake in the Chicago Metropolitan Area was from 91 to 95 percent efficient in removing suspended sediment and from 76 to 94 percent efficient in removing copper, iron, lead, and zinc from urban runoff. Sediments accumulated in the lake in the form of an organic-rich mud at an average rate of 20 millimeters per year; this reduced lake storage and covered potential habitat for aquatic organisms. Copper, lead, and zinc concentrations were closely associated with suspended-sediment concentrations and with silt- and clay-sized fractions of lake sediment. Although concentrations of mercury and cadmium were near detection limits in runoff, measurable concentrations of these metals accumulated in the lake sediments.     

PREDICTING THE SUMMER TEMPERATURE OF SMALL STREAMS IN SOUTHWESTERN WISCONSIN1

ABSTRACT: One of the biggest challenges in managing cold water streams in the Midwest is understanding how stream temperature is controlled by the complex interactions among meteorologic processes, channel geometry, and ground water inflow. Inflow of cold ground water, shade provided by riparian vegetation, and channel width are the most important factors controlling summer stream temperatures. A simple screening model was used to quantitatively evaluate the importance of these factors and guide management decisions. The model uses an analytical solution to the heat transport equation to predict steady‐state temperature throughout a stream reach. The model matches field data from four streams in southwestern Wisconsin quite well (typically within 1°C) and helps explain the observed warming and cooling trends along each stream reach. The distribution of ground water inflow throughout a stream reach has an important influence on stream temperature, and springs are especially effective at providing thermal refuge for fish. Although simple, this model provides insight into the importance of ground water and the impact different management strategies, such as planting trees to increase shade, may have on summer stream temperature.     

STORMFLOW AND SEDIMENT LOSS FROM INTENSIVELY MANAGED FOREST WATERSHEDS IN EAST TEXAS1

ABSTRACT: Five small (4 ha) forested watersheds in East Texas were instrumented in December 1980 to determine the effect of forest harvesting, mechanical site preparation, and livestock grazing on stormflow, peak discharge rate, and sediment loss. After three pretreatment years, four of the watersheds were treated as follows: (1) clearcutting followed by roller chopping; (2) clearcutting following by shearing and windrowing; (3) clearcutting following by shearing, windrowing, and continuous grazing; and (4) clearcutting followed by shearing, windrowing, and rotational grazing. Clearcut harvesting and all site preparation treatments significantly increased stormflow, peak discharge, and sediment losses over the undisturbed condition. Roller chopping and shearing/windrowing had little impact on sediment loss from these watersheds and appears to be a sound forest conservation practice for gently sloping watersheds (> 8 percent). As applied, livestock grazing had minimal impact on stormflow and peak discharge. The moderately stocked continuously grazed treatment had little impact on sediment loss, but the high stocking density of the rotational grazing treatment increased sediment losses over the undisturbed condition. Sediment losses from these intensively managed forest watersheds, even though significantly greater than from undisturbed conditions, were within the range of sediment losses from undisturbed watersheds in the Southeast, below the range of losses from mechanically prepared watersheds elsewhere, and well below potential losses from pasture and cropland.     

EVALUATION OF THE MAXEY-EAKIN METHOD FOR ESTIMATING RECHARGE TO GROUND-WATER BASINS IN NEVADA1

AESTRACT An evaluation of the Maxey-Eakin method for calculating recharge to ground-water basins in Nevada was performed. The evaluation consisted of comparing Maxey-Eakin estimates with independent estimates of recharge, and analyzing the nature of the differences between the groups of estimates. In the comparison with the Maxey-Eakin estimates, two different groups of independent estimates were used: (1) 40 recharge estimates that were identified from water budgets contained in reports by the Nevada Department of Conservation and Natural Resources and (2) 27 recharge estimates that were identified from previous studies that used models. The results of the comparisons indicate generally good agreement between the Maxey-Eakin estimates and both groups of independent estimates. To quantify this agreement, an analysis was conducted to estimate the uncertainty in the Maxey-Eakin method. The analysis produced an upper bound on the standard deviation of the Maxey-Eakin estimate for a given basin. For the group of 40 water-budget estimates, the upper bound on the standard deviation for an individual basin is 4,800 acre-ft/yr, and the corresponding coefficient of variation of the Maxey-Eakin estimate is no greater than 44 percent. For the group of 27 model estimates, the upper bound on the standard deviation is 4,100 acre-ft/yr, and the corresponding coefficient of variation is no greater than 24 percent.     

WATER RESOURCES APPLICATIONS OF STREAM CHANNEL CHARACTERISTICS ON SMALL FORESTED BASINS1

ABSTRACT. Stream channel characteristics were found to be useful indices to the hydrology of 27 small forested basins in the Northeast United States. Channel width alone explained 37 percent of the variation in mean annual runoff, whereas channel width combined with basin area explained 78 percent of the variation in mean annual runoff. This approached the percentage of variation in mean annual runoff explained by mean annual precipitation (83 percent). A simulated 15% increase in precipitation, such as might occur in a weather modification project, produced increases in channel width, depth, and channel area of 3, 4, and 8 percent, respectively.     

ACCUMULATION OF AS,NI, CU,AND PB IN RETENTION AND RECHARGE BASINS SOILS FROM URBAN RUNOFF1

ABSTRACT: The accumulation of arsenic, nickel, copper, and lead in the soil profile was determined beneath five urban storm-water retention/recharge basins used by the Fresno Metropolitan Flood Control District, California. Soils were sampled from the surface to the first zone of saturation and compared with soils from an adjacent un-contaminated control site. These elements were found to be accumulating in the first few centimeters of basin soil and are important to the effectiveness of a specific best management practice, i.e., the retention and recharge of urban storm water. Study basins in use since 1962, 1965, and 1969 had lead contents in the 0–2 cm soil depth interval‘of 570, 670, and 1400 mg Pb/kg soil, respectively. The median indigenous soil lead concentration was 4.6 mg/kg soil. The practice of removing excess flood runoff water from two basins by pumping apparently is a factor in reducing the accumulation rate of these elements in the surface soils of the basins.     

RUNOFF AND SEDIMENT PRODUCTION FROM BURNED FOREST SITES IN THE GEORGIA PIEDMONT1

ABSTRACT: Runoff and sediment production was measured under simulated and natural rain from 1×5 m plots established on a cutover and burned mixed pine-hardwood site in the Georgia Piedmont. Trees on the study site were cut and removed without mechanical disturbance. Slash was removed, kiln dried and replaced on the slope, and burned prior to plot installation. Three slopes, two rainfall intensities, three rainfall simulations representing three soil moisture conditions, and two replicate plots were used. The experiment was repeated four times during the period July 1989-July 1990 to investigate the effects of temporal changes in surface conditions and particularly root mat and residual forest floor decemposition. Runoff and sediment production from natural rainfall events was also measured from these plots during the period February-October 1990. Results of all measurements indicate that runoff and sediment production were generally low because of the protection afforded by the residual forest floor following burning. However, temporary hydrophobic conditions caused by a dry organic layer produced relatively high runoff rates and high sediment for the first few minutes of runoff for some of the simulated rainfall applications.     

SPNM,A MODEL FOR PREDICTING SEDIMENT,PHOSPHORUS, AND NITROGEN YIELDS FROM AGRICULTURAL BASINS1

ABSTRACT: A model called SPNM from the words “sediment-phosphorus-nitrogen model” was developed for simulating agricultural contributions to water pollution. SPNM is designed to predict sediment, P, and N yields for individual storms on small basins and to route these yields through streams and valleys of large basins. Users need no computer programming experience because the model is a problem-oriented computer language. SPNM is useful in planning water resources projects and in research. Tests of the model on a watershed provided realistic results.     

STORM WATER RUNOFF QUALITY FROM THREE LAND-USE AREAS IN SOUTH FLORIDA1

ABSTRACT: Storm water runoff studies of three small basins (20, 40, and 58 acres) in the Fort Lauderdale area of Florida were conducted by the U.S. Geological Survey in 1974–78. The basins were homogeneously developed with land uses being: commercial, single family residential, and high traffic volume highway. Synchronized data were collected for rainfall, storm water discharge, storm water quality, and bulk precipitation (rainfall plus dry fallout) quality. Analysis of the storm water discharge data showed that most runoff was from impervious areas hydraulically connected to drain inlets. Regression analyses of the storm water discharge and water quality data indicated that storm loads from the single family residential area correlated strongly with peak discharge and length of antecedent dry periods. Storm loads from the highway area correlated strongly with rainfall and less strongly with peak discharge and antecedent dry periods. Storm loads from the commercial area correlated strongly with peak discharge and rainfall, and less strongly with antecedent dry periods. On a unit area basis, the single family residential area yielded the largest loads of nitrogen, phosphorus, and dissolved solids. The commercial area yielded the largest loads of lead, zinc, and chemical oxygen demand. Yields of carbon were about the same for the three areas. Constituent loadings derived directly from the atmosphere were estimated on the basis of bulk precipitation samples and compared with storm runoff loads from the highway and commercial areas.     

APPLICATION OF THE BASINS DATABASE AND NPSM MODEL ON A SMALL OHIO WATERSHED1

ABSTRACT: The purpose of this study was to evaluate the Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) watershed management system. BASINS data were used with the NPSM model to predict discharge and sediment concentrations at the outlet of a 103 km² Ohio watershed. It was concluded that the NPSM model should always be calibrated but only a few of the parameters provided with BASINS needed to be calibrated. For a three‐year study period, there was a 2 percent underestimation of discharge using area weighted precipitation values and a 25 percent overestimation using the single station data in BASINS. A comparison of observed and predicted monthly discharge resulted in an r² of 0.86 with area‐weighted precipitation and an r² of 0.74 with the single station data. Calibrating the model to substantially improve sediment predictions was unsuccessful and we concluded that a calibration period of one year was too short. For the three‐year study period, the r² for sediment was 0.36 with a slope of 0.37 and an intercept of 18.8 mg/l. The mean observed and predicted sediment concentrations were 27.1 mg/l and 22.6 mg/l, respectively.     

A COMPARISON OF DELTA CHANGE AND DOWNSCALED GCM SCENARIOS FOR THREE MOUNTAINOUS BASINS IN THE UNITED STATES1

ABSTRACT: Simulated daily precipitation, temperature, and runoff time series were compared in three mountainous basins in the United States: (1) the Animas River basin in Colorado, (2) the East Fork of the Carson River basin in Nevada and California, and (3) the Cle Elum River basin in Washington State. Two methods of climate scenario generation were compared: delta change and statistical downscaling. The delta change method uses differences between simulated current and future climate conditions from the Hadley Centre for Climate Prediction and Research (HadCM2) General Circulation Model (GCM) added to observed time series of climate variables. A statistical downscaling (SDS) model was developed for each basin using station data and output from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEPINCAR) reanalysis regridded to the scale of HadCM2. The SDS model was then used to simulate local climate variables using HadCM2 output for current and future conditions. Surface climate variables from each scenario were used in a precipitation‐runoff model. Results from this study show that, in the basins tested, a precipitation‐runoff model can simulate realistic runoff series for current conditions using statistically down‐scaled NCEP output. But, use of downscaled HadCM2 output for current or future climate assessments are questionable because the GCM does not produce accurate estimates of the surface variables needed for runoff in these regions. Given the uncertainties in the GCMs ability to simulate current conditions based on either the delta change or downscaling approaches, future climate assessments based on either of these approaches must be treated with caution.     

HYDROLOGY OF A SMALL IMPOUNDMENT AND WATERSHED IN CENTRAL OKLAHOMA1

ABSTRACT: West Bitter Creek floodwater retarding structure site 3 in South Central Oklahoma was instrumented and records obtained and analyzed to obtain information concerning an impoundment water budget that is useful to landowners and designers of these impoundments. On-site loss of water from the impoundment was only 17 percent of the inflow during three years when the annual precipitation averaged 26 inches and the annual inflow averaged 1.4 inches. Runoff from an eroded area with no farm ponds was about 70 percent greater per unit area than from a portion of the watershed where 71 percent of the drainage area was controlled by farm ponds. A previous study indicated, however, that the ponds were reducing runoff only 13 percent. Loss of top soil increases runoff considerably. Only 24 percent of the total runoff into the impoundment was base flow. The flow rate into the impoundment was less than 0.05 cfs 70 percent of the time, and the inflow rate exceeded 10 cfs only 1 percent of the time. SCS runoff curve numbers varied between 57 and 96 for the impoundment watershed with an inverse relation between precipitation amount and curve number apprently caused by partial area runoff from impervious and semi-impervious areas. A comparison of measured event runoff versus event runoff computed by the SCS curve numbers gave an r² of only 0.44. However, the total computed surface runoff for eight years of record was less than 1 percent below the measured runoff which indicated the curve number method was a good tool for predicting long term runoff for the watershed.     

PREDICTING PEAK STREAM FLOW FROM AN UNDISTURBED WATERSHED IN THE CENTRAL APPALACHIANS1

ABSTRACT: Data from a small forested catchment were used to model peak stream flow as a function of basic hydrologic variables associated with 112 rain storms. Rainfall depth and initial stream flow rate accounted for 87.1 percent of peak flow variability. Forty expressions of rainfall intensity (describing both the temporal sequence of intensity for 20 equal storm intervals, and maximum intensity for 20 separate interval lengths) were used in an attempt to improve the predictability of basic models. None of the intensity parameters improved predictability by as much as 2 percent, apparently because the most intense rainfall bursts generally occurred near the beginning of storm periods. Mean rainfall intensity for entire storms was generally as effective as any of the shorter interval intensities, and its use helped to linearize the relationship between peak flow and rainfall depth and duration.     

ACID PRECIPITATION AND WEATHERING BY ORGANIC ACIDS IN LABRAI)OR LAKE BASINS1

ABSTRACT: Thirty-five lakes in southern Labrador sampled in 1981 were resampled in 1989 and water chemistry values were compared between visits. Results showed higher pH, specific conductance, acid neutralization capacity, color, and base cations values in 1989, though sulfate, the ion most likely to reflect acid precipitation impacts, did not vary. The major ion changes measured were probably due to natural hydrological variations and not to changes in acid inputs. Results from the 1989 data showed a slight, but significant, decrease in water sulfate concentration trend from western to eastern Labrador, though most values, even in the western portion of the study area, fell close to the values considered “background” by Brakke et at. (1989). Base cation concentrations exceeded those which could be predicted from weathering by carbonic and bicarbonic acid. Assuming that little weathering is generated by acid precipitation in this region, the excess cations measured are probably a result of bedrock dissolution from organic acids generated by plant decomposition. Calculations showed that organic acid effect could be responsible for 9 to 52 percent of total weathering in the study basins.     

AN EVALUATION OF THE HYDROLOGIC SOIL GROUPS AS USED IN THE SCS RUNOFF METHOD ON RANGELANDS1

The U.S. Soil Conservation Service has developed a method for estimating runoff for small watersheds when stream flow data are not available. The technique is based on a simplified infiltration model of runoff using various kinds of soil, land use, and empirical approximation.     

SEDIMENT,NITRATE, AND AMMONIUM IN SURFACE RUNOFF FROM TWO TAHOE BASIN SOIL TYPES 1

ABSTRACT: Few studies have addressed the natural pollution potential of pristine subalpine forested watersheds on a site-specific basis. Consequently, specific source and amounts of nutrient discharge to tributaries of the Tahoe Basin are difficult to identify. The sediment content and nitrate and ammonium levels in surface runoff from two soil types (Meeks and Umpa), four plot conditions (wooded natural and disturbed, open natural and disturbed), and three slopes (gentle, moderate, and steep) were studied using rainfall simulation that applied a 9 cm h¹, 1-h event. A significant (P ≤ 0.005) two-way interaction between soil type and plot condition affected runoff nitrate concentration. Runoff from natural or disturbed open plots contained significantly (P = 0.05) greater nitrate than wooded plots. Peak concentrations of nitrate commonly occurred during early runoff, suggesting that peak nitrate discharge to Lake Tahoe tributaries can be expected during early runoff from snowmelt and summer precipitation events. The highest nitrate runoff concentration and 1-h cumulative loading from the 0.46 m² plots were 6.7 mg L-¹ (Umpa, open natural, 15–30 percent slope), and 0.7 mg (Umpa, open natural, ≥ 30 percent slope), respectively. Ammonium in surface runoff was generally below detection limits (≤ 0.05 μg L^?1). No statistical relationship between runoff nitrate and sediment discharge was detected.