Dissertation
Modeling Hydrological Processes and Key Factors Influencing Nonpoint Source Pollution in Agricultural and Urban Settings
Washington State University
Doctor of Philosophy (PhD), Washington State University
2023
DOI:
https://doi.org/10.7273/000006336
Abstract
Nonpoint-source pollution from agricultural and urban landscape is a major threat to water quality worldwide. This doctoral research aims to assess the spatiotemporal variations of nonpoint-source pollution and elucidate key factors at play in representative agricultural and urban settings in the US Pacific Northwest (PNW). The main objectives were to:1) elucidate the long-term historical soil erosion trend, as affected by climatic and management conditions;
2) assess changes in water erosion as impacted by the projected future climate and the effect of conservation practices using WEPP; and
3) optimize placement of rain gardens in an urbanizing watershed, south Puget Sound, using the Hydrologic Sensitivity Index (HSI) method.
For the first study, I delineated a watershed within the low-, intermediate-, and high-precipitation zones of eastern Washington, and simulated water erosion over two time periods: past and present, under different tillage practices and crop rotations. The average annual erosion rates decreased from the past by 32%, 57%, and 70%, respectively, for the three watersheds. The decrease was due to the combined effects of changing climate and implementation of conservation practices.
For the second study, I modeled water erosion for the same three watersheds for two time periods: historical and future using downscaled climates. Future average annual precipitation and daily temperature increase by 4–6% and 7–10%, respectively. Projected annual water erosion generally decreased by 0–4% for the three watersheds, owing to improvement in winter conditions. Future annual water erosion exceeds 50 Mg ha−1 in areas with steeper slopes and years with wheat, especially in intermediate-, and high-precipitation zones. I recommend targeted land management practices for erosion reduction.
In the third study, I used the HSI approach to identify areas prone to runoff generation and suitable areas for rain gardens, a small-scale Green Stormwater Infrastructure (GSI). I conducted hydrologic modeling to assess the adequacy of the HSI method. The simulated runoff was positively correlated with HSI. The locations most suitable for rain gardens were concentrated in the northeastern-central parts of the study watershed. This study demonstrated the adequacy of HSI method and provided a strategy for practitioners and regulatory personnel in optimizing the placement of rain gardens.
Findings from this dissertation advance the understanding of nonpoint-source pollution and contribute to conservation planning in both agricultural and urban areas.
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Details
- Title
- Modeling Hydrological Processes and Key Factors Influencing Nonpoint Source Pollution in Agricultural and Urban Settings
- Creators
- Mugal Samrat Dahal
- Contributors
- Joan Q. Wu (Advisor)Anand Jayakaran (Committee Member)Jan Boll (Committee Member)Kirti Rajagopalan (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Biological Systems Engineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 140
- Identifiers
- 99901087335901842
- Language
- English
- Resource Type
- Dissertation