Physicochemical effects of temperature and water chemistry on cohesive channel erosion
Abstract
One potential unforeseen consequence urbanization and climate change is accelerated stream channel erosion due to increased stream temperatures and changes in stream chemistry, which affect the surface potential and hence the stability of soil colloids. Summer thunderstorms in urban watersheds can increase stream temperature more than 7 degC and the impact of global warming on average stream temperature is already evident in some stream systems. The goal of this research was to evaluate the impact of changes in stream chemistry commonly observed in urban watersheds, and expected to occur due to climate change, on the fluvial erosion of cohesive streambank soils. We hypothesized that increases in stream temperature and changes in stream pH and salt concentrations alter the surface potential of clay particles, affecting soil erodibility. We tested this hypothesis by measuring the erosion rate of two riparian soils dominated by different common phyllosilicate clays in a recirculating hydraulic flume. Two pH levels (6, 8), three water temperatures (10 degC, 20 degC, 30 degC), and two NaCl concentrations (5 mg/l, 5 g/l) were analyzed. Velocity profiles and the distance to the soil sample were measured using a Sontek Vectrino II acoustic Doppler profiler. Additionally, zetapotential was measured to determine if erosion rates were correlated to changes in clay surface potential due to varying water chemistry. Initial study results indicated significant increases in erosion rates for both clay types with decreasing pH and increasing water temperature; temperature effects were more significant than pH effects. Changes in erosion rates with salt concentration were only significant for the soil with montmorillonite clay. While the research is ongoing, these initial results could have wide-ranging implications for climate change and urban stormwater management. Assuming climate change will result in higher stream temperatures and lower stream pH, streambank erosion could accelerate in currently stable stream systems with cohesive banks. Additionally, new stormwater management and urban design techniques may be needed to manage runoff temperature and pH, in addition to current techniques for reducing runoff peak flow and volume from developed lands.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMEP53B0833W
- Keywords:
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- 1625 GLOBAL CHANGE Geomorphology and weathering;
- 1815 HYDROLOGY Erosion;
- 1825 HYDROLOGY Geomorphology: fluvial