Institute of Ecosystem Studies

2009 BES Annual Meeting Presentation and Poster Abstracts

Model-based rating curves for the expanded Gwynns Falls streamflow monitoring network
Miller, Andrew
Co-Authors: Andrew Miller, Garth Lindner, Philip Larson, and Claire Wellty, UMBC

Abstract: Nine stream gages added to the Gwynns Falls monitoring network in the last 18 months were installed in collaboration with USGS and are currently being maintained by UMBC personnel using funding sources that will run out within 1 year. To establish valid rating curves we are using a combination of direct discharge measurements at low to intermediate flows, with flagging and field survey of water levels at intermediate through overbank flows. A 2-d hydraulic model (TUFLOW) simulates water-surface elevation and velocity and is used to match the lower part of the rating curve and extend it to cover the maximum flood of record. Topographic information to support the model is derived from LiDAR supplemented by total-station surveys of the channel bed. Preliminary observations indicate that some stream gages have hysteretic rating curves. The difference between discharges for the same stage on the rising and falling limb can be up to 20-30% even for in-channel flows that are less than 1 m deep, and larger differences may occur at flood stage. These patterns have implications for interpretation of discharge records and use of flow data to estimate dissolved and particulate loads. Based on our results we recommend that at some sites it is advisable to develop separate rating curves for the rising and falling limbs, and to develop a range of modeling scenarios for predicting the range of potential uncertainty.