Thesis
WEPP simulation of water erosion on cereal grain cropland in the inland Pacific Northwest
Washington State University
Master of Science (MS), Washington State University
12/2020
DOI:
https://doi.org/10.7273/000004206
Handle:
https://hdl.handle.net/2376/125244
Abstract
The inland Pacific Northwest (PNW) is characterized warm, dry summers and wet winters with three (high, intermediate, and low) precipitation zones. In the inland PNW, high erosion rates are attributed to hilly topography, highly erodible silt loam soil, rainy winter seasons with frequent freeze-thaw events, and widespread use of conventional tillage practices. A 1978 USDA study showed that annual water erosion from cropland in the region's Palouse River basin averaged 20.6 t ha−1. A more recent 2009 study reported simulated average annual erosion rates of 10, 13, and 11 t ha−1 for the low-, intermediate-, and high-precipitation zones, with erosion in the intermediate-precipitation zone exceeding the tolerable limit of 11 t ha−1 despite increase of conservation practices. Identifying source areas for targeted, effective management requires understanding the factors affecting water erosion, especially how tillage practices and crop rotation interact in various topographic, soil, and climatic settings. The objectives of this study are to (i) understand how hillslope hydrological and water erosion processes are influenced by key environmental factors (soil, climate, topography) and management practices (tillage, crop rotation), and (ii) assess the spatial distribution of soil erosion for each county and precipitation zone over the last 30 years. I addressed these objectives by compiling various combinations of soil, climate, topography, tillage and crop rotation and simulating these combinations county by county with WEPP. WEPP simulations show that erosion rate is lowest in the low-precipitation zone and highest in the intermediate-precipitation zone, exceeding the tolerable limit in many cases. Temporally, high precipitation events and fallow periods in the rotation greatly increase erosion. Average annual erosion rates in Whitman County are 8.2, 13.8, and 9.8 t ha−1 in the low-, intermediate-, and high-precipitation zones. The intermediate-precipitation zone has the greatest total annual erosion, 3.0×106 t, despite having the smallest area. Columbia County has the highest erosion rate with 17.9 t ha−1 yr−1. GIS maps based on the simulations reveal critical-source areas ("hotspots") where estimated erosion rates are more than five times the average rates, providing crucial information for, and advancing our understanding of, targeting management and increasing efficiency of conservation practices.
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Details
- Title
- WEPP simulation of water erosion on cereal grain cropland in the inland Pacific Northwest
- Creators
- Mugal Samrat Dahal
- Contributors
- Joan Qiong Wu (Chair) - Washington State University, Department of Biological Systems EngineeringR Troy Peters (Committee Member) - Washington State University, Department of Biological Systems EngineeringJan Boll (Committee Member) - Washington State University, Department of Civil and Environmental EngineeringAnand Jayakaran (Committee Member) - Washington State University, WSU Extension ANR
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Biological Systems Engineering
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 95
- Identifiers
- 99900896437401842
- Language
- English
- Resource Type
- Thesis