| dc.description.abstract |
Water resource management has altered the natural flow regime of rivers around the
globe. Buffers to environmental risk and uncertainty, dams balance competing demands
for water storage and release for human needs. While dams have served as a cornerstone
for human development, they have historically been tied to river exploitation, jeopardizing
ecological health and species richness of streams and rivers. This project seeks to
assess the impacts of current reservoir management practices on downstream ecological
integrity in a changing climate with a focus on rainfall distribution shifts. We assess
these impacts in a ‘model-world’ that captures some of the complexities existing in
natural systems while enabling various dam management scenarios to operate under controlled
conditions. For this reason, a lumped three-part mathematical model was developed
to represent the impacts of precipitation and dam management on the stability of a
simplified food web operating downstream from the dam. First, a watershed routing
model was derived to link precipitation statistics and watershed land cover properties
using a prescribed unit hydrograph. Second, a nonlinear reservoir model linking inflow,
outflow and storage behind the dam was used to generate distinct patterns of streamflow
variability downstream of the dam. Last, the dynamics of a three species food web
were coupled to the aforementioned flow downstream from the dam so as to determine
whether reservoir operations can sustain the downstream food web stability. This three-part
lumped model was operated under five reservoir management scenarios: Natural flow
variability, run of river, minimum flow management, drought management, and flood
management. Using predictions from the IPCC AR5 Report (2013), changes in precipitation
frequency and depth due to long term shifts in the climate were evaluated assuming
long-term annual precipitation is not altered. By simulating multiple reservoir management
scenarios, it is envisaged that reservoir operators can accommodate ecological integrity
explicitly. As expected, flow variability was found to decrease substantially in each
of the four dammed scenarios when compared to an unregulated flow regime, with the
range of flows shifting from 105-108 to 4-5 105 m3/day. With less frequent and more
intense storms, the outflow from the reservoir shifted towards less frequent, higher
magnitude flow rates in each scenario. None of the scenarios tested maintain populations
in all trophic levels for the duration of the modeling period when faced with high
variability in rainfall inter-arrival times. Presently, reservoir managers operating
their dams under run of river or flood management will achieve the greatest downstream
ecological integrity. However, as precipitation patterns shift from more frequent
and less intense to less frequent and more intense storms, these reservoir types are
most at risk to ecological degradation. The downstream food web appeared to be resilient
to a changing precipitation pattern in a minimum flow management scenario, indicating
that current management practices that preserve “ecological integrity” may be advantageous
in an uncertain climate future. While the study’s findings support that minimum flow
regulation may be one of the best management approaches in a changing climate, the
top trophic level is only maintained during 33.6% of the modeling time period for
said management scenario. Continued efforts should be made to optimize reservoir management
practices so as to improve ecological integrity in an uncertain future. Serving as
a first attempt at linking shifts in precipitation statistics, hydrology, reservoir
management, and ecology, this study provides new insight into the effects of dam management
on downstream food web dynamics, allowing reservoir managers to assess the impacts
of their management decisions to preserve ecological integrity.
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