Formation and decay of a tributary-dammed lake, Laonong River, Taiwan

Abstract

We use field observations, laboratory experiments, and mathematical theory to characterize the full life cycle of a tributary-dammed lake. The natural lake formed in August 2007 at the confluence of the Laonong River, southern Taiwan, with a steep tributary. Due to heavy rains from typhoons Wutip and Sepat, the tributary delivered massive amounts of sediment to the confluence. This caused damming of the trunk river, the growth of a lake, and the demise of a bridge upstream of the confluence. The lake lasted until October 2007, gradually decaying due to incision and infill by subsequent stream flow. We reconstruct the episode using hydrological records, ground observations, and surveyed profiles. We then use the event to verify a mathematical theory of river and lake bed evolution. The theory is based on a diffusion description of river morphodynamics, constrained by backwater effects due to lake formation. After validation using laboratory experiments, the theory is applied to the Laonong field event. Good agreement is obtained between calculated and surveyed long profiles. The theory can also reproduce the complex stage hydrograph recorded upstream of the confluence. This suggests a role for simplified, but laboratory-tested mathematical theory in quantitative investigations of fluvial processes in the field. Copyright 2010 by the American Geophysical Union.