Geomorphic features of Lake Havasu with impacts on its water resource capacity

Abstract

Wilson DC. 2024. Geomorphic features of Lake Havasu with impacts on its water resource capacity. Lake Reserv Manage. 40:93–108. Determining a reservoir’s available storage capacity and its possible rate of change over time through in-filling are 2 of many parameters needed to conduct efficient and flexible water delivery operations, particularly in cascading river-reservoir systems. This study focused on this issue through generating the first bathymetric elevation map of Lake Havasu on the Colorado River (CR) with enough detail to identify geomorphic features, including areas of deposition, to assess the current storage capacity of the reservoir. Two main areas of deposition were identified, the CR inlet delta and the Bill Williams River (BWR) delta at the reservoir’s northern and southern ends, respectively. The physical distribution of the CR inlet deposits well into the main reservoir and to some extent those of the BWR delta also may have been influenced by one episode of drastic water level lowering early in the reservoir’s history that probably re-mobilized sediments when fluvial dynamics temporarily resumed. High resolution sonar images compared with the CR channel position on a pre-reservoir topographic map, a sonar-generated reservoir bottom hardness map coupled with grain-size analyses of sediment samples, and modeling reservoir water level changes support this notion. Post-reservoir dam construction up both rivers has cut off sediment sources that historically reached Lake Havasu, effectively reducing sedimentation rates. Determined thicknesses of the sediment packages indicate that Lake Havasu has lost more than 7% of its available storage capacity since inception, which is an important parameter for adjusting management of water deliveries and storage in the Colorado River system.