Date of Graduation
Master of Science in Environmental Management (MSEM)
Gretchen Coffman, Ph. D.
Rivers around the world are being degraded due to alteration of natural flow regimes caused by the creation of dams and diversions to serve human needs for water. Alteration to natural flow regime affects a river’s flow magnitude, frequency, duration, timing, and rate of change of flow. These changes have major repercussions on the processes that drive riparian ecosystems. Repercussions to river processes are manifested in the degradation of riparian forest health. This is evident in the rivers of California’s Central Valley, where altered flow regimes are present in all of its major rivers. As a result, Salicaceae spp. are not regenerating at historic rates and older trees are senescing. This dominant riparian tree family is dwindling due to these factors. Altered and historic flow regimes of Central Valley Rivers differ greatly. The most critical differences include an overall decrease in flow magnitude, an absence of winter flood peaks, and severe alteration to winter baseflow and snowmelt recession components of the hydrograph. The rate of flow decrease during the snowmelt recession is crucial to the recruitment of Salicaceae spp. It is recommended that flow rate decrease at 1 to 3 cm d-1. This range of flow rates allows for the root system of Salicaceae spp. to remain in contact with the receding instream and groundwater flows. Timing of these rates should correspond with Salicaceae seed release which range from mid-April to late May for Populus fremontii and from mid-May to late June for Salix spp. While much research has been conducted to prescribe environmental flows in the Central Valley, little has been done to ensure that these environmental flows regimes are effective. It is recommended that monitoring protocol be implemented that assesses the effectiveness of the Central Valley environmental flow regime. Recommendations have also been made to improve flow planning framework and implement an adaptive management approach to river restoration. These recommendations will promote the success of environmental flow prescriptions in the Central Valley and around the world.
Torrez, Nicholas J., "Environmental Flow Regime Recommendations for the Promotion of Salicaceae Seedling Recruitment in California’s Central Valley" (2014). Master's Projects. 26.