Upper Mississippi River Restoration Program

Upper Mississippi River Restoration Program

Long Term Resource Monitoring

 

The Long Term Resource Monitoring Program

An element of the Upper Mississippi River Restoration - Environmental Management Program

Development of two-dimensional numerical hydraulic models for Mississippi River Pool 13 and Illinois River La Grange Pool in support of the LTRMP

Upper Mississippi River Restoration - Environmental Management Program U. S. Army Corps of Enineers

Introduction/Background:

The primary objective is to numerically model selected Mississippi River and Illinois River Pools in order to develop the capability to relate hydraulic parameters for various alternative conditions to requirements for diverse biota enhancement. Two-dimensional flow models provide good simulations of current velocity patterns and water surface elevations for selected conditions. These numerical models provide water level management tools required for Habitat Needs Assessment (HNA) by presenting or quantifying information related to the following:

  1. System-wide high resolution topographic data
  2. System-wide bathymetric data
  3. Substrate type characterization
  4. Habitat spatial structure metrics
  5. Areas of inundation
  6. The existing and pre-impoundment hydrologic regime
  7. Analysis of seasonal habitat availability.

Model information is essential for characterizing aquatic habitat conditions as related to the hydrologic regime for floodplain habitats. The numerical models provide tools to evaluate and maximize opportunities for success in planning and designing as well as monitoring habitat improvement projects. The development of two-dimensional numerical hydraulic pool models will provide timely management tools as "on-the-shelf" models in support of the LTRMP. Numeric models have previously been developed for a number of pools and reaches on the Upper Mississippi River and Illinois Waterway for other projects. Refinement of these models offers an opportunity to develop appropriate tools for LTRM purposes economically and efficiently. Previous models were limited by the general lack of availability of off-channel bathymetric data. However, as part of ongoing efforts under the LTRM program, detailed bathymetric data for off-channel areas is available or being collected. In addition, most of the models were constructed to examine low to moderate flow conditions when the river remains within its banks, and little attempt has been made to include overbank flows in the two-dimensional models. Overbank flow is related to higher less frequent flows and are of significant interest since these flows are influential in changing conditions along bank lines and backwaters. The entire floodplain may be defined as the area inundated by the 100-year flood event and may include a much greater area than that inundated by the 2-year event. Area and frequency of inundation predicted by the model can provide a valuable frame of reference to that observed by the monitoring program. For LTRMP, models should extend to the land-water interface created by the 2 year frequency flood event. If it is desired to examine higher flood flow conditions, the overbank areas within the models will be extended for specific study areas. This will add significant costs. However, in general extending the models to the 100-year flood level is not expected to add much valuable information for LTRMP purposes compared to that provided by 2-year models.

Relevance of research to UMRS/LTRMP:

It is desired to eventually have calibrated, two-dimensional models for all of the navigation pools on the UMRS and to incorporate the velocity and depth information derived from the models into GIS to assist in Habitat Rehabilitation and Enhancement Projects (HREP) decision making and design. Specific objectives will include:

Methods to be Employed:

The models will be constructed by the Hydrologic Engineering Section of the Rock Island District, Corps of Engineers (CEMVR-ED-HH) using the Surface-Water Modeling System (SMS). The hydrodynamic model to be used in this effort is RMA2 (RMA = River Management Associates). This is considered a powerful model in that it is robust and stable with well accepted accurate results when properly calibrated. A three dimensional model may be considered more powerful but would involve significantly greater costs.

Pool 13 and the LaGrange Pool will be enhancements to the existing Pool models. The models were originally constructed using existing pool-wide bathymetry collected through the LTRMP for Pools 13 and LaGrange in 1997 and 1998, respectively. The model will be updated with newer bathymetric and floodplain topographic datasets, where available. Models will include existing channel regulating structures, utilizing the best available information about each structure. The existing models are inappropriate for use by the LTRMP in that they do not represent the existing conditions in adequate detail to establish and quantify the relationships between the monitored parameters and the project features. These relationships are what lend credibility to the monitoring process. If accurate relationships between physical forces and project design parameters to impacts on the biota are not established then monitoring has no relationship to habitat enhancement. Monitoring is then reduced to a passive activity with minimal interest to the observer only.

Calibration and verification of the models will be to prototype measurements of stage, water surface profiles, current velocities and flow distributions already available or collected as part of this effort. The Water Quality and Sedimentation Section (CEMVR-ED-HQ) will make the prototype measurements of velocity and flow distribution with an Acoustic Doppler Current Profiler.

Model outputs will be converted to shapefiles or coverages for use with ESRI ArcGIS software package. Model outputs may include inundation boundaries, velocity magnitudes, contours, etc.
Model and Survey Data Specifications: The hydraulic numerical models will be calibrated to elevation (accuracy of 0.2 feet), flow (5% accuracy) and velocity measurements (accuracy of 0.3 fps). Model Mesh resolution will be limited to a maximum of 300-foot element size. The mesh near regulating structures, in narrow side channels and near specific study areas will be refined as necessary. The hydrographic surveys will be assembled from navigation channel maintenance surveys, dam periodic inspection surveys, and environment management project surveys. The horizontal accuracy of the hydrographic survey data is the accuracy usually attributed to the US Coast Guards Differential GPS (DGPS). The published accuracy of this system is +/- 9 feet (horizontal). The vertical accuracy is published as being +/- 0.5 ft as per ASPRS Class III Standards as stated in the USACE EM1110-1-1000, dated 31 March 1993.

The floodplain digital terrain models have been developed from 1998 aerial photography and photogrammetry. This data will be used to extend the models, as requested, to incorporate the floodplain and islands above the 2 year water surface. Mississippi and Illinois River floodplain ("bluff-to-bluff") digital terrain model data was designed to adequately define elevated roads, railroads, levees and major topography changes. The data was compiled so that spot elevations on well-defined features would be within 0.67 feet (vertical) of the true position (as determined by a higher order method of measurement) 67% of the time. The 0.67 feet (vertical) is as per ASPRS Class I Standards as stated in the USACE EM 1110-1-1000, dated 31 March 1993.

Principle investigator/Project leader:

Marvin Martens CEMVR-ED-HH

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