Estimating Water Storage Capacity of Existing and Potentially Restorable Wetland Depressions in a Subbasin of the Red River of the North

Concern over flooding along rivers in the Prairie Pothole Region
has stimulated interest in developing spatially distributed hydrologic
models to simulate the effects of wetland water storage on peak river
flows. Such models require spatial data on the storage volume and
interception area of existing and restorable wetlands in the watershed
of interest. In most cases, information on these model inputs is
lacking because resolution of existing topographic maps is inadequate
to estimate volume and areas of existing and restorable
wetlands. Consequently, most studies have relied on wetland area to
volume or interception area relationships to estimate wetland basin
storage characteristics by using available surface area data obtained
as a product from remotely sensed data (e.g., National Wetlands
Inventory). Though application of areal input data to estimate volume
and interception areas is widely used, a drawback is that there is
little information available to provide guidance regarding the
application, limitations, and biases associated with such
approaches. Another limitation of previous modeling efforts is that
water stored by wetlands within a watershed is treated as a simple
lump storage component that is filled prior to routing overflow to a
pour point or gaging station. This approach does not account for
dynamic wetland processes that influence water stored in prairie
wetlands. Further, most models have not considered the influence of
human-induced hydrologic changes, such as land use, that greatly
influence quantity of surface water inputs and, ultimately, the rate
that a wetland basin fills and spills.

The goals of this study were to (1) develop and improve
methodologies for estimating and spatially depicting wetland storage
volumes and interceptions areas and (2) develop models and approaches
for estimating/simulating the water storage capacity of potentially
restorable and existing wetlands under various restoration, land use,
and climatic scenarios. To address these goals, we developed models
and approaches to spatially represent storage volumes and interception
areas of existing and potentially restorable wetlands in the upper
Mustinka subbasin within Grant County, Minn. We then developed and
applied a model to simulate wetland water storage increases that would
result from restoring 25 and 50 percent of the farmed and drained
wetlands in the upper Mustinka subbasin. The model simulations were
performed during the growing season (May October) for relatively wet
(1993; 0.67 m of precipitation) and dry (1987; 0.32 m of
precipitation) years. Results from the simulations indicated that the
25 percent restoration scenario would increase water storage by 2732
percent and that a 50 percent scenario would increase storage by
5363 percent. Additionally, we estimated that wetlands in the
subbasin have potential to store 11.5720.98 percent of the total
precipitation that fell over the entire subbasin area (52,758 ha). Our
simulation results indicated that there is considerable potential to
enhance water storage in the subbasin; however, evaluation and
calibration of the model is necessary before simulation results can be
applied to management and planning decisions.

In this report we present guidance for the development and
application of models (e.g., surface area-volume predictive models,
hydrology simulation model) to simulate wetland water storage to
provide a basis from which to understand and predict the effects of
natural or human-induced hydrologic alterations. In developing these
approaches, we tried to use simple and widely available input data to
simulate wetland hydrology and predict wetland water storage for a
specific precipitation event or a series of events. Further, the
hydrology simulation model accounted for land use and soil type, which
influence surface water inputs to wetlands. Although information
presented in this report is specific to the Mustinka subbasin, the
approaches and methods developed should be applicable to other regions
in the Prairie Pothole Region.
[Summary provided by the USGS.]