Water Temperature, pH, and Road Salt Impacts on the Fluvial Erosion of Cohesive Streambanks

Siavash Hoomehr,Matthew Eick,Theresa Wynn-Thompson,Waverly Garnand,Akinrotimi Akinola

doi:10.3390/w10030302

Abstract

Increasing human populations and global climate change will severely stress our water resources. One potential unforeseen consequence of these stressors 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. The objectives of this study were to determine the effect of water temperature, pH, and salinity on streambank erosion rates; determine how erosion rates vary with clay mineralogy; and, explore the relationship between zeta potential and erosion rate. Remolded samples of natural montmorillonite- and vermiculite-dominated soils were eroded in a recirculating hydraulic flume under multiple shear stresses (0.1–20 Pa) with different combinations of water temperature (10, 20, and 30 °C), pH (6 and 8), and deicing salt (0 and 5000 mg/L). The results show that erosion rates significantly increased with increasing water temperature: a 10 °C increase in water temperature increased median erosion rates by as much as a factor of eight. Significant interactions between water pH and salinity also affected erosion rates. In freshwater, erosion rates were inversely related to pH; however, at high salt concentrations, the influence of pH on erosion rates was reduced. Results of this study clearly indicate water chemistry plays a critical role in the fluvial erosion of cohesive streambanks and suggest that channel protection efforts should include controls for stream temperature, in addition to peak flow rates, to maintain channel stability.

Highlights

Streambank retreat and the resulting sediment pollution threaten the sustainability of urban stream systems and surface water supplies
To account for variability in erosion rates caused by slight differences in the applied shear stress and to create dimensionless erosion rates, the erosion rate (Er)
As with the vermiculite soil, increases in the montmorillonite soil erosion rates with increasing water temperature at pH 6 were statistically significant for the low salinity water but not for the higher salinity water

Summary

Introduction

Streambank retreat and the resulting sediment pollution threaten the sustainability of urban stream systems and surface water supplies. Urbanization increases stormwater runoff quantity, timing, and chemistry: the resulting channel enlargement and migration damage the adjacent urban infrastructure, including sewer and water lines, utilities, buildings, and bridges [1]. The eroded sediment becomes a water pollutant. Excess suspended sediments reduce the diversity and abundance of aquatic organisms, increase the need for dredging, reduce hydropower and water supply reservoir capacity, increase drinking water treatment costs, and serve as a carrier for contaminants such as phosphorus, bacteria, heavy metals, pharmaceuticals, and pesticides. In the United States alone, the annual cost of water erosion due to on-site and off-site damages, including nutrient loss, habitat depletion, sedimentation, and flooding, as well as the cost associated with erosion prevention, have been estimated as greater than 20 billion dollars [2].

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