D. Applications and Discussion
The capabilities provided within WetScape may be best illustrated through examples of how the analysis modules and tools might be used in practice. Modules may be used individually or applied in a sequence that is selected according to project objectives and analysis requirements. For quick review or simple tasks, a single module could be applied when project objectives can be accomplished by one type of analysis. Local tools may be used in iterative steps to develop a composite watershed map consisting of optimized sites and projected siting alternatives.
The interaction between spatial model user modes and tools can be powerful if applied with careful attention to interpretation stages. Sequence application may be desirable to extend project planning from initial development to more detailed analysis, or as a means to refine an evaluation through a series of transfers and interactive cycles between capabilities. Examples of possible sequences include BWS/PWA (regional screening followed by site selection and local optimization), or PWA/BWA (evaluation of local areas to prepare a composite map for analysis according to selected performance criteria).
The current development of WetScape allows a broad variety of terrain-based conditions to be examined and allows hierarchical refinement of the analysis as more detailed information is obtained. The approach bridges a basic gap between technology that is available for local (e.g. CADD) and systematic (e.g. DEM, DLG) data types, to create an appraisal-level GIS that is hierarchical in application. Additional capabilities have been considered that could be easily incorporated in to the modular framework described.
Recent research in spatial modeling applied to water storage issues presented in WetScape 3.0 has resulted in an a collection of tools and techniques required to evaluate the water storage characteristics of natural terrain features. Several elements of technology have been explored and preliminary tools have been developed to analyze water holding catchments contained in the undulating terrain for the prairie pothole region of eastern North Dakota.
The wetland / storage analysis technology developed by IDS researchers strives to emphasize goals that pursue low maintenance, ecologically and hydrologically sustainable storage catchments that support any number of pertinent management objectives (e.g. water retention, water quality improvement, habitat values enhancement, etc.). Adopting a terrain based emphasis as an analysis foundation permits the user to conduct the analysis with the premise that alternatives and scenarios generated are achievable and practical at the implementation level without the need for significant support over the life of the project. The technology utilizes computer language and tool approaches to achieve an analysis and is readily available for exploration.
2.1 Synopsis of the Problem:
The upper portion of the Devils Lake basin, located near Devils Lake, North Dakota, has been experiencing rising flood levels which may be associated with a wetter hydrologic period and increased runoff collecting in lakes within the region. This proposal describes a computation analysis estimating the storage volume within the basin that is made up of prairie pothole terrain, and provide numerical insight on the potential gains from a program that would recapture of storage volume from previously dewatered prairie pothole land.
The project area involves an entire sub-basin which is located in the north eastern portion of North Dakota. The sub-basin of interest drains southward to the Devils Lake area over terrain that is predominantly prairie pothole in form. The sub-basin lies North of the Sheyenne River currently no prominent release of this water as surface water exists. Several large lakes exist within the basin and many remain as permanent water surfaces throughout the year. The majority of the storage is found in prairie pothole formations ranging widely in size.
2.2 Flooding due to Lost Attenuation associated with changing land use of pothole terrain:
The Devils Lake, North Dakota community is a well established urban center, located on nearly all sides of Devils Lake. In recent years many facilities continue to be threatened by rising water levels within the lake. Since concern regarding the impact of flooding prompts the evaluation of changes that could be affordably implemented in the upper basin by recapturing lost storage volume that would attenuate the flood waters.
One explanation for the increased surface runoff at the lakes may be attributed to the changes to the land use and land management practices in the most recent twenty to fifty years involving the conversion of prairie pothole lands to more favorable conditions to support agriculture by draining standing water and bringing the land into a more readily farmable condition. Several land reclaiming activities are described by hydraulic engineers to have been undertaken by local farmers. One low cost, popular approach often pursued in prairie pothole country involves breaching the natural impoundment and draining the land. The resulting reclaimed land is without the hindrances of boggy conditions and is farmed without significant land movement using contour plowing and similar techniques. These corrections associated with draining activities tend to be small in scale and may not be reflected in the elevation terrain models developed for the area.
2.3 Possible Approaches for Analysis:
IDS group has been asked to research and develop analysis tools for wetland systems, particularly the prairie pothole condition found in northeastern North Dakota by the Reclamation-LSWQ group. This research has lead to the creation of the Natural Resources Workstation (NRWS) and the WetScape decision support systems. As part of that effort, several dozen commercially of the shelf (COTS) USGS Digital Elevation Model (DEM) digital product files have been acquired containing elevation in a lattice form with 30 meter horizontal resolution. The vertical resolution of the elevation model is either in 1 meter or 1 foot intervals, depending on the quadrangle. These files have been used to create a GIS elevation map layer with thirty meter horizontal resolution.
IDS group has conducted a preliminary feasibility analysis to demonstrate the proof of concept of terrain modeling for potential storage volume with success using the USDA 1:24K 7.5minute DEM data. Several representative quadrangles were chosen to study the resolving power of the low cost COTS data product.
Additional sources of spatial data are available in part for the Devils Lake, North Dakota area that could be used to possibly better represent the unique prairie pothole terrain that shapes the landscape. The COTS and custom digital mapping products could facilitate and extend computer assisted analysis of catchment analysis. Specific computer analysis capabilities could facilitate the process of identifying the potential volume of storage in the Devils Lake basin. With adequate horizontal and vertical resolving power offered by various data sets and analysis techniques, improved estimates could be made to study the distributed storage capacity of the prairie potholes that drain to the Devils Lake area and remain trapped in the currently closed basin.
In order to conduct an analysis of lost attenuation, a few simplifying assumptions can be made, and then validated as part of the analysis. If we safely assume the surface runoff experience in recent years in the Devils Lake area to be predominantly controlled by surface water flows, and that local flooding levels act a response frequency considerably greater than the groundwater recharge rates and conveyance rates, then a terrain based analysis may shed some light to possible value from selected breached pothole closure thereby trapping surface runoff and lessoning downstream flooding.
Fundamental to answering the question us a careful examination of the size, shape and texture of the wetland pothole features that can be detected using the USGS standard data products that are under development. The alternative is to prepare an expensive custom data product without a prior assurance that the results would warrant the cost.