			Home About us Contact

Curve Number (curve + number)

Distribution by Scientific Domains

Engineering	100%

Selected Abstracts

EFFECT OF ORIENTATION OF SPATIALLY DISTRIBUTED CURVE NUMBERS IN RUNOFF CALCULATIONS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2000
Glenn E. Moglen
ABSTRACT: The NRCS curve number approach to runoff estimation has traditionally been to average or "lump" spatial variability into a single number for purposes of expediency and simplicity in calculations. In contrast, the weighted runoff curve number approach, which handles each individual pixel within the watershed separately, tends to result in larger estimates of runoff than the lumped approach. This work proposes further enhancements that consider not only spatial variability, but also the orientation of this variability with respect to the flow aggregation pattern of the drainage network. Results show that the proposed enhancements lead to much reduced estimates of runoff production. A revised model that considers overland flow lengths, consistent with existing NRCS concepts is proposed, which leads to only mildly reduced runoff estimates. Although more physically-based, this revised model, which accounts directly for spatially distributed curve numbers and flow aggregation, leads to essentially the same results as the original, lumped runoff model when applied to three study watersheds. Philosophical issues and implications concerning the appropriateness of attempting to disaggregate lumped models are discussed. [source]

An improved AMC-coupled runoff curve number model

HYDROLOGICAL PROCESSES, Issue 20 2010
Ram Kumar Sahu
Abstract In the Soil Conservation Service Curve Number (SCS-CN) method, the three levels of antecedent moisture condition (AMC) permit unreasonable sudden jumps in curve numbers, which result into corresponding jumps in the estimated runoff. A few recently developed SCS-CN-based models obviate this problem, yet they have several limitations. In this study, such a model incorporating a continuous function for antecedent moisture has been presented. It has several advantages over the other existing SCS-CN-based models. Its application to a large dataset from US watersheds showed to perform better than the existing SCS-CN method and the others based on it. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Effects of Watershed Impervious Cover on Dissolved Silica Loading in Storm Flow,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2007
Socratis Loucaides
Abstract:, Dissolved silica (DSi) availability is a factor that affects the composition of algal populations in aquatic ecosystems. DSi cycling is tightly linked to the hydrological cycle, which is affected by human alterations of the landscape. Development activities that increase impervious cover change watershed hydrology and may increase the discharge of DSi-poor rainwater and decrease the discharge of DSi-rich ground water into aquatic ecosystems, possibly shifting algal community composition toward less desirable assemblages. In this study, DSi loadings from two adjacent coastal watersheds with different percent impervious cover were compared during four rain and five nonrain events. Loadings in the more impervious watershed contained a significantly larger proportion of surface runoff than base flow (ground-water discharge) and had lower [DSi] water during rain events than the less impervious watershed. Application of the Soil Conservation Service Curve Number (CN) method showed that the minimum rainfall height necessary to yield runoff was significantly lower for the more impervious watershed, implying that runoff volumes increase with impervious cover as well as the frequency of runoff-yielding events. Empirical data collected during this study and estimates derived from the CN method suggest that impervious cover may be responsible for both short-term DSi limitation during rain events as well as long-term reduction of DSi inputs into aquatic ecosystems. [source]

SENSITIVITY CONSIDERATIONS WHEN MODELING HYDROLOGIC PROCESSES WITH DIGITAL ELEVATION MODEL,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2001
Sung-Mm Cho
ABSTRACT: The purpose of this paper is to investigate the sensitivity of a hydrologic models to the type of DEM used. This was done while modeling basin water quality with 1:24,000 and 1:250,000 U.S. Geological Survey DEMs as input to model hydrological processes. The manner in which the model results were sensitive to the choice of raster cell size (scale) is investigated in this study. The Broadhead watershed, located in New Jersey, USA, was chosen as a study area. Curve numbers were estimated by a trial and error to match simulated and observed total discharge. Monthly runoff for the watershed was used in the calibration process. Higher runoff volumes were simulated by the model when the 1:24,000 DEM were used as input data, probably due to the finer resolution which simulated increased average slope and hence higher estimated runoff from the watershed. As the simulated slope of the watershed is flatten with the 1:250,000 DEM, the response of stream flow was delayed and simulated less runoff volume. (KEY TERMS: DEM; curve number; sensitivity analysis; runoff volume; water quality; calibration.) [source]

Incorporating variable source area hydrology into a curve-number-based watershed model

HYDROLOGICAL PROCESSES, Issue 25 2007
Elliot M. Schneiderman
Abstract Many water quality models use some form of the curve number (CN) equation developed by the Soil Conservation Service (SCS; U.S. Depart of Agriculture) to predict storm runoff from watersheds based on an infiltration-excess response to rainfall. However, in humid, well-vegetated areas with shallow soils, such as in the northeastern USA, the predominant runoff generating mechanism is saturation-excess on variable source areas (VSAs). We reconceptualized the SCS,CN equation for VSAs, and incorporated it into the General Watershed Loading Function (GWLF) model. The new version of GWLF, named the Variable Source Loading Function (VSLF) model, simulates the watershed runoff response to rainfall using the standard SCS,CN equation, but spatially distributes the runoff response according to a soil wetness index. We spatially validated VSLF runoff predictions and compared VSLF to GWLF for a subwatershed of the New York City Water Supply System. The spatial distribution of runoff from VSLF is more physically realistic than the estimates from GWLF. This has important consequences for water quality modeling, and for the use of models to evaluate and guide watershed management, because correctly predicting the coincidence of runoff generation and pollutant sources is critical to simulating non-point source (NPS) pollution transported by runoff. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Simulating daily soil water under foothills fescue grazing with the soil and water assessment tool model (Alberta, Canada)

HYDROLOGICAL PROCESSES, Issue 15 2004
Emmanuel Mapfumo
Abstract Grazing is common in the foothills fescue grasslands and may influence the seasonal soil-water patterns, which in turn determine range productivity. Hydrological modelling using the soil and water assessment tool (SWAT) is becoming widely adopted throughout North America especially for simulation of stream flow and runoff in small and large basins. Although applications of the SWAT model have been wide, little attention has been paid to the model's ability to simulate soil-water patterns in small watersheds. Thus a daily profile of soil water was simulated with SWAT using data collected from the Stavely Range Sub-station in the foothills of south-western Alberta, Canada. Three small watersheds were established using a combination of natural and artificial barriers in 1996,97. The watersheds were subjected to no grazing (control), heavy grazing (2·4 animal unit months (AUM) per hectare) or very heavy grazing (4·8 AUM ha,1). Soil-water measurements were conducted at four slope positions within each watershed (upper, middle, lower and 5 m close to the collector drain), every 2 weeks annually from 1998 to 2000 using a downhole CPN 503 neutron moisture meter. Calibration of the model was conducted using 1998 soil-water data and resulted in Nash,Sutcliffe coefficient (EF or R2) and regression coefficient of determination (r2) values of 0·77 and 0·85, respectively. Model graphical and statistical evaluation was conducted using the soil-water data collected in 1999 and 2000. During the evaluation period, soil water was simulated reasonably with an overall EF of 0·70, r2 of 0·72 and a root mean square error (RMSE) of 18·01. The model had a general tendency to overpredict soil water under relatively dry soil conditions, but to underpredict soil water under wet conditions. Sensitivity analysis indicated that absolute relative sensitivity indices of input parameters in soil-water simulation were in the following order; available water capacity > bulk density > runoff curve number > fraction of field capacity (FFCB) > saturated hydraulic conductivity. Thus these data were critical inputs to ensure reasonable simulation of soil-water patterns. Overall, the model performed satisfactorily in simulating soil-water patterns in all three watersheds with a daily time-step and indicates a great potential for monitoring soil-water resources in small watersheds. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Modeling Postfire Response and Recovery using the Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS),

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 3 2009
Kristina Cydzik
Abstract:, This paper investigates application of the Army Corps of Engineers' Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) to a burned watershed in San Bernardino County, California. We evaluate the HEC-HMS' ability to simulate discharge in prefire and postfire conditions in a semi arid watershed and the necessary parameterizations for modeling hydrologic response during the immediate, and subsequent recovery, period after a wildfire. The model is applied to City Creek watershed, which was 90% burned during the Old Fire of October 2003. An optimal spatial resolution for the HEC-HMS model was chosen based on an initial sensitivity analysis of subbasin configurations and related model performance. Five prefire storms were calibrated for the selected model resolution, defining a set of parameters that reasonably simulate prefire conditions. Six postfire storms, two from each of the following rainy (winter) seasons were then selected to simulate postfire response and evaluate relative changes in parameter values and model behavior. There were clear trends in the postfire parameters [initial abstractions (Ia), curve number (CN), and lag time] that reveal significant (and expected) changes in watershed behavior. CN returns to prefire (baseline) values by the end of Year 2, while Ia approaches baseline by the end of the third rainy season. However, lag time remains significantly lower than prefire values throughout the three-year study period. Our results indicate that recovery of soil conditions and related runoff response is not entirely evidenced by the end of the study period (three rainy seasons postfire). Understanding the evolution of the land surface and related hydrologic properties during the highly dynamic postfire period, and accounting for these changes in model parameterizations, will allow for more accurate and reliable discharge simulations in both the immediate, and subsequent, rainy seasons following fire. [source]