Spatial dynamic groundwater regulation to ensure adequate instream flows for salmon

Instream flow management;targeted environmental policy;stream depletion;groundwater regulation;salmon

Han, Jae J. ; Brozović ; Nicholas

关键词: Instream flow management;    targeted environmental policy;    stream depletion;    groundwater regulation;    salmon;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/26080/Han_Jae.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Competing demands for scarce water resources have led to conflict in semi-arid and arid regions. Such conflicts often involve the need to restrict the use of groundwater pumping in irrigated agriculture in order to leave adequate quantities of water for fish species in nearby streams. Groundwater pumping can lead to a reduction in instream flows of nearby streams in a process known as stream depletion. From an economic standpoint, policies intended to leave adequate quantities of water instream for any purpose should aim to minimize the welfare losses accrued by irrigated agriculture due to reduced pumping. To this effect, prior studies have utilized spatial characterization of the hydrologic systems in question to spatially target water allocation between groundwater irrigators and instream demands (Young et al. 1986, Keplinger et al. 1998, McCarl et al. 1999, Kuwayama and Brozovic 2011). However, the policies developed or analyzed in these studies usually focus on meeting aggregate instream flow goals on a seasonal or yearly basis rather than meeting them on a continuous basis. In this thesis, I present a dynamic optimization framework that solves for optimal groundwater pumping allocations in a stream-aquifer system with instream flow goals that need to be met on a daily basis. An analytical hydrology model is integrated into the framework to constrain stream depletion impacts on a daily basis to ensure that minimum instream flow requirements for ecological needs are met on a daily basis. I apply this framework to the Scott River Basin in northern California, which is a region where extensive irrigation by farmers has harmed the local coho salmon species by reducing the natural flows of stream habitats. The coho salmon have been listed as Threatened under the state and federal Endangered Species Acts, and therefore must be protected. The results indicate that wells located farther from the stream should generally be allocated more water in most hydrologic scenarios. A counterintuitive exception to this general finding is that wells located closer to the stream should be allocated more water when there is a period of extreme scarcity in the instream water supply during the year. This result is driven by the fact that there is a time lag associated with the stream depletion externality following pumping, and this time lag varies with location relative to the stream. Thus, any period of time during the year with extreme water scarcity requires a cessation of pumping in advance of that period so that stream depletion impacts can adequately dissipate before the start of the period. Wells that are farther away from the stream cause higher stream depletion impacts following the cessation of pumping, so they would need to cease pumping earlier in advance of the period ofextreme water scarcity. Finally, my analysis suggests that in the Scott River Basin, targeted daily groundwater pumping limits tailored to individual irrigators may lead to welfare costs that are over 30% less than that of the corresponding uniform reduction policy in which all irrigators are restricted equally. The relative welfare gains of the targeted policy over the uniform reduction policy increase as the scarcity of the instream water supply increases.