Comparing flow laws for remote sensing of discharge: Tanana River Alaska
Abstract
Remote sensing of river discharge is a rapidly growing field, wherein simple flow laws (such as the Manning-Strickler equation) are combined with remote sensing observations to predict streamflow. In this paper we explore the accuracy of remotely sensed discharge for a braided Tanana River in Alaska, USA using two sets of remotely sensed observations of river height, width, and slope. In the first set of observations, height, width and slope are measured via ArcticDEM using WorldView meter scale imagery. In the second set of observations, nadir altimeters and optical imagery are used to measure river height and width respectively, along with a constant slope from ArcticDEM. Specifically, we evaluated 2 variants of Manning's equation, which measures river discharge. Model 1 had a constant friction coefficient, or "n", and model 2 had a varied coefficient, varying based on the river's hydraulic depth. For both models we calculated the parameters (the friction coefficient and the other unobserved variables in Manning's equation) by using a portion of the observed measurements as calibration data. The other fraction of observed data was used as validation to compare the accuracy of model 1 and 2 by computing the normalized RMSE (nRMSE). For the ArcticDEM data, we found that some reaches indicated a time-varying n was appropriate, with n at low flow increasing markedly as predicted by theory. For the second set of observations, we found very little difference in the error statistics between the 2 models: one of the observed reaches had an nRMSE of 12.86% for model 1 and 12.87% for model 2. Thus, preliminary results seem to indicate that the higher precision ArcticDEM measurements indicate a need for the more complex flow law, with time-varying n. These results have implications for flow laws to use in the context of the upcoming Surface Water and Ocean Topography (SWOT) mission.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH040.0011W
- Keywords:
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- 1855 Remote sensing;
- HYDROLOGY;
- 1857 Reservoirs (surface);
- HYDROLOGY;
- 1860 Streamflow;
- HYDROLOGY;
- 4512 Currents;
- OCEANOGRAPHY: PHYSICAL