This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/ldr.2727 This article is protected by copyright. All rights reserved. ESTIMATING SEDIMENT DELIVERY RATIOS FOR GRASSED WATERWAYS USING WEPP Harsh Vardhan Singh 1,2 , 1 Post-doctoral Research Associate, 2 Former Graduate Student, hsingh_29320@yahoo.com John Panuska 2 , Distinguished Faculty Associate, jcpanuska@wisc.edu Anita M. Thompson 2 , Professor, amthompson2@wisc.edu 1 Tropical Research and Education Center, 18905 SW 280th St, Homestead, FL 33031 2 Biological systems Engineering Department, University of Wisconsin, 460 Henry Mall, Madison, Wisconsin 53706 Correspondence Harsh Vardhan Singh, Post-doctoral Research Associate, Tropical Research and Education Center, 18905 SW 280th St, Homestead, FL 33031, USA. Email: hsingh_29320@yahoo.com ; Telephone: (334) 524-6047 ABSTRACT Grassed waterways (GWWs) transport sediment and nutrients from upland source areas to receiving waters. Watershed planners have a critical need to understand GWW sediment delivery to optimally target source area management practices. Better physically-based tools are needed to estimate sediment delivery by GWWs. This study developed several distributed sediment delivery ratio (SDR) regressions for GWWs using the process-based Water Erosion Prediction Project (WEPP) model to provide simple equations to estimate sediment delivery for planning applications. WEPP was calibrated and validated for runoff and sediment yield for large 30.2 ha and smaller 5.7 ha nested watersheds with terraces and a common GWW outlet. A crop rotation of corn, oat and alfalfa and fall tillage using chisel plow were used in the nested watersheds. A hypothetical management case without terraces using corn,