Long-term flow regulation in a semi-arid river results in landscape-scale biophysical changes

Keywords: historical ecology, geomorphology, succession, flow modeling, dammed river, geographic information systems (GIS), arid regions, height above river (HAR), restoration ecology, ecological restoration
Abstract Type: Paper Abstract

Abstract

Putah Creek is a regulated, semi-arid river in California’s Sacramento Valley, one that experienced dramatic and permanent biophysical changes after the construction of Monticello Dam. Its story is a common one in the Mediterranean state; there are well over 1,000 dams in California, and the bulk of dammed water is located in the Sacramento Valley. This study’s geographic analyses show Putah Creek went from an ephemeral flash-and-scour system, with a mostly-barren channel and oak woodland-covered natural levees, to a perennial system, with dense riparian forest in the channel and on the banks. Regulation after the construction of Monticello Dam in 1957 resulted in much-reduced peak streamflows and elimination of over-bank floodplains but maintenance of a small year-round baseflow. Additionally, dredging eliminated in-channel floodplains and slowed flow, leading to dramatic ecological changes on the reach scale.

Myriad GIS workflows were synthesized in a variety of software, including HEC-ras, Pix 4D, ENVI, ArcGIS Pro, and ArcMap, in order to compare historic hydrology-vegetation dynamics to modern dynamics. Primary datasets included historic topographic quadrangles, historic aerial photos, modern satellite imagery, LiDAR-collected topography, and peak streamflow records. Methods and results from this study will form the foundation of future novel succession models for small, regulated, semi-arid river systems, especially for similar systems in the Sacramento Valley, to analyze past restoration effects and predict future reach-scale restoration outcomes.