216-Sedimentation Analysis for Existing and Proposed Development Conditions.

Abstract

A sedimentation analysis was carried out to investigate a fluvial system in Big Tujunga Wash, Los Angeles, California. The study area is located on a braided channel complex, which has been subject to flooding during past years. The main channel traversing the study area branches into north and south branches and is subject to split flows during larger floods. The bed material is composed of sand, coarse gravel, cobbles and boulders. Proposed conditions include the construction of a golf course at the site. The purpose of this study is to examine if the golf course has any adverse impact in Tujunga Wash via comparison of aggradations/scour for existing and proposed conditions. The Modified Universal Soil Loss Equation (MUSLE) was selected for computing the sediment yield from a single event. Sediment analyses were conducted using HEC-6 for both existing and proposed conditions. The HEC-6 analysis was based on a previous hydraulic study using HEC-RAS. For proposed conditions, the grading of the golf course was designed such that the flow and sediments would be conveyed through the most likely natural flow paths and to ensure that the golf course would not act as a sediment trap. The hydraulic and sediment transport analyses utilized a simplified representation of the complex channel network actually present in Big Tujunga Wash and Haines Canyon. Model results for both existing and proposed conditions were very similar, despite the uncertainty in estimating sediment loads, uncertainty in sediment analysis, and the potential variation of key parameters during high flows.