An Examination of Stormwater Quality and Quantity in Austin Area Creeks

Weizhen Zhu
Roger Glick


The Large Watershed Study is an ongoing project of the Environmental Resources Management Division of the Watershed Protection Department. We used U.S. Geological Survey flow gauge stations and some stream stations of our own as locations to obtain stormwater samples in local streams. Rainfall data was collected to correspond to these stations through the City FEWs gauge system as well as data downloaded from NexRad weather radar. Storm and base flow was separated using a variety of techniques. Water quality data wasobtained from both discrete sampling at first which each aliquot was analyzed and mathematically flow-weighted to arrive at an event mean, and samples flow weighted and manually composited based on flowmeter records before laboratory analysis. A wide variety of conventional and toxic pollutant parameters were analyzed. Watershed characterizations of impervious cover, land use, and groupings based on development condition were also added information. Analysis included careful processing and quality control resulting in a set of baseflow ratios, event mean concentrations, impervious cover, rainfall, and hydrologic metric statistics for each site over time. Site summary statistics characterized each location. Linear regression with time indicated trends were used as well as linear regression of BFR with IC and rainfall to explore these relationships across the gauge data. Trends of EMCs with time and linear relationships of EMC with peak flowrate and rainfall were evaluated. Annual pollutant loads were looked at with respect to impervious cover and average annual rainfall and multiple regression was used to look at effect of peak flowrate on the change in EMC over time. Although this monitoring project has been ongoing since the 1980’s, each discrete period of reporting has specific questions to be answered from the data analysis due to current regulatory and technology issues related to hydrology and stormwater management. This period sought answers to questions beneficial to low impact development s