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

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.

Fluvial Erosion Rate of Cohesive Streambanks Is Directly Related to the Difference in Soil and Water Temperatures

“…In addition to reducing variability in the erosion rates resulting from slight differences in the hydraulic shear stress, this normalization also created nondimensional erosion rates. Shear velocity ( u *) values were determined by fitting velocity profile data in the log‐law region to the rough “law of the wall” equation given below (Hoomehr et al, 2018): where U is the streamwise velocity at a distance ( y ) from the soil surface, u * is the shear velocity, k is the von Karman constant (0.4), and y 0 is the roughness height.…”

“…It is also possible to have elevated streambank temperatures relative to that of the stream flow since the loss of riparian shade and the presence of urban infrastructure such as pipelines and utility lines, as well as modern technologies such as bridge deck deicing systems using thermal energy sources, can result in localized elevated soil temperatures. Water temperature was shown to be positively correlated with the fluvial entrainment of remolded cohesive soils (Hoomehr et al, 2018). Although previous research has shown the importance of the physicochemical properties of soil and water on cohesive soil erosion (Grissinger, 1966; Partheniades and Paaswell, 1970; Sargunam et al, 1973; Arulanandan et al, 1975), the effect of water temperature on cohesive soil erosion has not been fully explored, while the effect of soil temperature on erosion is largely unknown.…”

Streambank Erosion: Advances in Monitoring, Modeling and Management

“…The research articles included in this special issue specifically targeted three areas that are key to better understanding streambank erosion and failure, namely, monitoring [8][9][10][11], modeling [12][13][14][15][16][17], and management [18][19][20][21]. As an ensemble, the articles highlight the value of monitoring campaigns to characterize the effect of external drivers (e.g., hydrologic events), the capabilities and limitations of numerical models for predicting the response of the system (e.g., stream restoration design), and the effectiveness of management practices to prevent and mitigate the impacts of streambank erosion and failure.…”

“…Their results emphasize the importance of selecting an adequate stabilization technique to manage bank erosion, while considering the associated cost and performance under extreme conditions. Hoomehr et al [21] carried out flume experiments to study the effect of water temperature, pH, and salinity on bank erosion rates. Their results indicate that erosion rates are affected by water temperature, with higher rates as temperature rises.…”

“…The research articles included in this special issue addressed some of these challenges, as well as shed light on some topics that deserve further exploration. The latter topics include: (1) examining the effect of stratigraphic position on the quantification of sediment and total phosphorus loading to streams [19]; (2) accounting for the effects of vegetation, meandering, and weakening and weathering processes in the development, calibration, and application of numerical models [12,14,17]; (3) developing a better understanding of the physical mechanisms that govern gully progression and development, especially those in riparian areas [10]; (4) establishing a standardized procedure for running and post-processing the results of erodibility tests [15]; and (5) developing a better understanding of influential factors such as water chemistry on streambank erosion [21].…”