| dc.description.abstract |
<p>Periods of drought and low streamflow can have profound impacts on both human and
natural systems. People depend on a reliable source of water for numerous reasons
including potable water supply and to produce economic value through agriculture or
energy production. Aquatic ecosystems depend on water in addition to the economic
benefits they provide to society through ecosystem services. Given that periods of
low streamflow may become more extreme and frequent in the future, it is important
to study the factors that control water availability during these times. In the absence
of precipitation the slower hydrological response of groundwater systems will play
an amplified role in water supply. Understanding the variability of the fraction of
streamflow contribution from baseflow or groundwater during periods of drought provides
insight into what future water availability may look like and how it can best be managed.
The Mills River Basin in North Carolina is chosen as a case-study to test this understanding.
First, obtaining a physically meaningful estimation of baseflow from USGS streamflow
data via computerized hydrograph analysis techniques is carried out. Then applying
a method of time series analysis including wavelet analysis can highlight signals
of non-stationarity and evaluate the changes in variance required to better understand
the natural variability of baseflow and low flows. In addition to natural variability,
human influence must be taken into account in order to accurately assess how the combined
system reacts to periods of low flow. Defining a combined demand that consists of
both natural and human demand allows us to be more rigorous in assessing the level
of sustainable use of a shared resource, in this case water. The analysis of baseflow
variability can differ based on regional location and local hydrogeology, but it was
found that baseflow varies from multiyear scales such as those associated with ENSO
(3.5, 7 years) up to multi decadal time scales, but with most of the contributing
variance coming from decadal or multiyear scales. It was also found that the behavior
of baseflow and subsequently water availability depends a great deal on overall precipitation,
the tracks of hurricanes or tropical storms and associated climate indices, as well
as physiography and hydrogeology. Evaluating and utilizing the Duke Combined Hydrology
Model (DCHM), reasonably accurate estimates of streamflow during periods of low flow
were obtained in part due to the model’s ability to capture subsurface processes.
Being able to accurately simulate streamflow levels and subsurface interactions during
periods of drought can be very valuable to water suppliers, decision makers, and ultimately
impact citizens. Knowledge of future droughts and periods of low flow in addition
to tracking customer demand will allow for better management practices on the part
of water suppliers such as knowing when they should withdraw more water during a surplus
so that the level of stress on the system is minimized when there is not ample water
supply.</p>
|
|
