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United States Department of Agriculture

Agricultural Research Service

Title: The Relationship Between Curve Numbers and Green-Ampt Effective Hydraulic Conductivities for Use in the Wepp Model

Authors
item Nearing, Mark
item Liu, B - PURDUE UNIV., W. LAF, IN
item Risse, L - UNIV OF GA, ATHENS, GA
item Zhang, Xunchang

Submitted to: American Water Resources Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 3, 1996
Publication Date: N/A

Interpretive Summary: The WEPP technology is a tool for conservation planning. It is used to help farmers and land managers make appropriate decisions about how to manage the land to reduce soil erosion. It is also used to make erosion assessments and inventory, that is, to determine how much erosion is occurring on the land so that society as a whole can know how much soil is being lost to erosion and to make better decisions as to how land should be managed on a broad geographical scale. This study was undertaken to help the user select certain important data values related to how much rain water infiltrates (goes) into the soil, and how much runs across the surface, thus carrying soil across and off the field. These data values are called conductivity, because they refer to the amount and rate of water the soil may conduct. Conductivity depends on the type of soil and the plant and animal biological characteristics of the soil. The results of the study provide a simple method to select conductivity values for any given soil or land management practice.

Technical Abstract: The SCS curve number method is an accepted method for estimating surface water runoff caused by rainfall. Several modern process-based hydrologic models, including the Water Erosion Prediction Project (WEPP) model, use the Green-Ampt infiltration equation, but the basis for selecting model parameters is not a s comprehensive as for curve number selection. The purpose of this study was to quantitatively relate curve numbers to Green-Ampt effective conductivity parameters, K**e, so that the information available relative to application of curve number technology may be applied to WEPP for predicting runoff from rainfall. Data used to develop relationships included descriptions of 43 soils, CLIGEN generated weather information for ten geographic locations in the U.S., and eight different types of cropping practices. Values of K**e were derived by optimizing WEPP model output to match that predicted by curve numbers for a 20 year weather sequence. Relationships were developed to describe the optimized K**e values for both fallow and cropped conditions. The relationships were tested on approximately 350 plot years of measured data from 11 runoff and erosion stations in the U.S. and shown to perform as well as or better than the SCS curve number approach for individual storm predictions of runoff volumes.

Last Modified: 12/21/2014
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