Date

2001

Document Type

Capstone Project

Degree Name

Bachelor of Science (B.S.)

Department

Science & Environmental Policy

Abstract

Land use practices and management does affect sediment load in water bodies. However, in small watersheds that have multiple land use types, it is much more difficult to extrapolate which land use practices are having more of an effect on sediment load. The following study examined the relationship between land use practices and sediment load in Gabilan Creek. Three general land use types are found within this 315.9km² watershed, grazing, agriculture (crops) and urban. Five winter season storm events were monitored for discharge, total suspended sediment, and bedload at 11 different sites throughout the watershed. Sites were chosen based on their accessibility, safety, and proximity to land use boundaries. Samples were taken at as many bridges as possible in as frequent of an interval as possible. Both suspended sediment and bedload samples were dried, filtered and weighed in the lab. Analysis of each sample were conducted and totaled for each event. Of the five events monitored only three had samples taken at all eleven sites. These three events were used as typical winter storm events for the Gabilan Watershed. Total area for each of the three general land use types was calculated using the Tarsier Modeling Framework. Total sediment loads for the three events were used with the land use areas to calculate sediment yield coefficients for each land use practice. Predictions for total suspended sediment and bedload per land use type were estimated using the sediment yield coefficients and land use areas. Results indicate that current agricultural practices are contributing a majority of both suspended sediment and bedload into Gabilan Creek. Urban areas also contribute a significant TSS load to the system, but have no effect on total bedload. Grazing area attributed to a significant portion of the overall bedload yields, but total TSS yields are considered nearly insignificant when compared to yields from crops and urban areas.

Comments

Capstone Project (B.S.) Earth Systems Science & Policy Institute

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