Seasonal nearshore sediment resuspension and water clarity at Lake Tahoe

Abstract

Reardon KE, Moreno-Casas PA, Bombardelli FA, Schladow SG. 2016 Seasonal nearshore sediment resuspension and water clarity at Lake Tahoe. Lake Reserv Manage. 32:132--145.Motivated by management challenges due to declining water clarity at Lake Tahoe, California–Nevada, we synthesized field observations and modeling of wind-driven nearshore sediment resuspension to inform decision-makers. We present the first field observations of nearshore sediment resuspension in both summer and winter and investigate seasonal differences in lake behavior. In addition, using a previously modified and validated wind-wave model, STWAVE, we developed management charts that illustrate relationships between fetch, wind intensity, and wave height and between water depth, wave height, and the potential for mobilization of different-sized particles. For a representative grain size of 150 μm, the wind-driven surface waves were found to influence the sediments to a maximum water depth of 9 m. Additionally, we evaluated the potential for wind-driven nearshore sediment resuspension with changing lake levels, considering a range of possible future scenarios. The areal extent of potential wind-driven sediment resuspension in Lake Tahoe's southern nearshore zone is maximum (8.3 km2) at a lake water level equal to the natural rim (1897 m). The potential for resuspension notwithstanding, the results demonstrated no increase in particle loading of the size class identified to most negatively impact water clarity (<16 μm). Therefore, we corroborate previous findings and conclude that wind-driven nearshore sediment resuspension does not contribute to the declining water clarity of Lake Tahoe and attribute this to a lack of available fine material within the lake sediments.