- Chesapeake/Delaware Bays Deepening Study -
CHT assisted the US Army Engineer Research and Development Center (ERDC) at Vicksburg, MS on this study. The purpose of the study was to assess the impact on salinity intrusion and circulation of deepening the navigation channels in the Delaware Bay, the C&D Canal, and the upper Chesapeake Bay from their existing authorized depths. The three-dimensional CH3DZ model was applied with and without channel deepening using boundary forcings from 1993 and 1965. The 1993 forcings contained several typical events such as large setups and set downs in the water surface, along with a large flood event. The hydrology of 1965 contained the drought of record for the region.
- Terrebonne Marsh Salinity Intrusion Model Study -
CHT conducted this study for the Vicksburg District of the US Army Corps of Engineers. The three dimensional numerical model know as CH3DZ was applied to assess the impact of salinity in the Terrebonne Marsh and the Atchafalaya Bay as a result of implementing channel deepening in the Atchafalaya River and Bayous Chene, Boeuf, and Black. Year long simulations were made for an average flow year and a low flow year with and without channel deepening. In addition, simulations were made with 50-year future bathymetry. Salinity contours plots were generated to illustrate the impact of channel deepening in the marsh and navigation channels.
- Atchafalaya Bay Bar Channel Study -
CHT conducted this study for the New Orleans District of the US Army Corps of Engineers. The purpose of the study was to predict the impact of deepening the Atchafalaya Bay bar channel on the formation and transport of fluid mud within the channel. In addition, the impact of various structural alternatives were investigated. A sediment transport fluid mud model was developed in the three-dimensional CH3DZ hydrodynamic model, resulting in a model called CH3DZ-FM. Field data collected by ERDC for the New Orleans District were employed to validate the numerical model.
- Freshwater Bayou Channel Deepening Study -
CHT is conducting a numerical modeling study for the New Orleans District of the US Army Corps of Engineers to determine the impact of channel deepening on shoaling and bank erosion in the Freshwater Bayou navigation channel located to the west of the Vermilion Bay in Louisiana. With the sediment being primarily fine-grained fluid mud, the CH3DZ-FM model previously developed to investigate sedimentation in the Atchafalaya Bar channel is being applied. Plans call for deepening the existing 12 ft channel to 16 ft. An interesting feature is a salinity barrier lock located near the Gulf end of Freshwater Bayou. For the September 2001 - August 2002 time period, the lock was closed about 85% of the time. Thus, the Freshwater Bayou bar channel is effectively disconnected from the GIWW and Vermilion Bay most of the time.
RESERVOIR CIRCULATION / WATER QUALITY
- Lake Washington -
CHT assisted the US Army Engineer Research and Development Center (ERDC) in the development and application of a three-dimensional (3D) hydrodynamic model of Lake Washington to provide flow fields to a 3D water quality model of the lake. Lake Washington is located near Seattle, WA. The CH3DZ hydrodynamic model was applied on the grid shown (with many vertical layers) for the years of 1995-97. During this period, sufficient data were available to set all freshwater inflows and wind forcing, along with the water surface elevation at the Hiram M. Chittenden Locks leading into Puget Sound. In addition, temperature data were available at several stations throughout the lake to aid in model validation. Velocity data collected in the 1970’s were employed to demonstrate the ability of the 3D hydrodynamic model to accurately compute the movement of lake waters during different periods of the year.
- Watts Bar Reservoir -
This study was conducted in support of obtaining the necessary water quality permit for the construction of two marinas on Watts Bar Reservoir on the Tennessee River. A major issue that had to be addressed was how quickly each of the marinas would be flushed and what the impact of the flushing would be on dissolved oxygen (DO) in the marinas. A CE-QUAL-W2 model existed, however since the reservoir is stratified in the summer and the lateral dimension was important in modeling the marinas adjacent to the river, a three-dimensional hydrodynamic model was constructed to determine the residence times for each marina. The CH3DZ model was employed. Data from 2002 were used to specify boundary conditions and to calibrate the model. Dissolved oxygen conditions were then assessed by treating each marina as a continuous stirred reactor, i.e., as a fully mixed body of water. In this analysis, values for inflowing DO, ultimate BOD, and SOD were required. Field data collected in 2006 provided the inflowing DO and ulitimate BOD. SOD was estimated from typical data for reservoirs.
STORM SURGE AND FREQUENCY OF OCCURRENCE
- Hilton Head Island and Vicinity Storm Surge Study -
CHT conducted this study for the Charleston, SC District of the US Army Corps of Engineers. The purpose of the study was to compute storm surge frequency-of-occurrence relationships that reflect tidal phasing as well as both tropical and extratropical storm events. The computational grid of the study encompasses the eastern Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. High resolution was provided in the Hilton Head Island study area such that the minimum grid spacing is on the order of several hundred meters. Recent high precision bathymetry data were interpolated onto the refined portion of the global grid. Tides and historically occurring tropical and extratropical storm events were simulated over the grid domain with peak surge values archived at selected locations in the study area. These data were then input to the EST model to develop frequency relationships for each location.
- Hurricane Induced Stage Frequency Analysis for the Hawaiian Islands -
CHT recently completed a hurricane-induced flood frequency study for the State of Hawaii. The study encompassed the six major Hawaiian Islands shown. The application required the selection of historical storms for input to the numerical long-wave storm surge model ADCIRC. Surge results were then used to compute frequency-of-occurrence relationships using the Empirical Simulation Technique. To perform a realistic storm surge analyis, it is crucial to define historical events that have impacted the islands in the study area. Selection of appropriate storm events made use of Eastern and Central North Pacific Basin Hurricane database of the National Hurricane Center. Candidate events were required to pass within 200 nautical miles of at least two of the islands with maximum winds at that point of at least 39 mph. Corresponding events have an equal probability of impacting each of the islands within the 200 nautical mile ellipse. Therefore, each event was translated by one Radius to Maximum wind across the study of 102 impacting events. Each of these hypothetical events was then used to generate wind and pressure fields for input to the ADCIRC model to compute storm surge at each of 522 predefined transect points. The generated database of storm surges was then input to the EST, a statistical model that simulates life-cycle sequences of cyclic but non-deterministic multi-parameter systems such as storm events and their corresponding environmental impacts. These databases of simulated life-cycle hurricanes were then post processed to generate mean value frequencey estimates with standard deviation confidence limits at each of the transect points.
- Olmsted Locks and Dam, Ohio River Study - CHT provided technical guidance and assistance to ERDC on the concept of using
1:60 section model and 1:120 general movable-bed model of Olmsted Locks and Dam, Ohio River. CHT partner, Tom Pokrefke, reviewed the testing program, met with the contractor, and provided guidance on data requirements, data measurements and analysis, and evaluation of various testing schemes. The Olmsted Locks and Dam project is presently under construction using an innovative, never performed, at this scale in the US, in-the-wet construction method. The test results from the section and general models were used to provide the contractor with specific construction sequences and potential problems during float-in, “sinking,” and placement.
- Ohio River Bank Stabilization Study
- CHT was part of a five-man team which conducted a site visit, discussed and developed alternatives, prepared design plans with justifications, and prepared a final report for the Ohio River at St. Marys, West Virginia. CHT worked with the US Engineer Research and Development Center (ERDC) in Vicksburg, MS and conducted the study for the Huntington District of the US Corps of Engineers. Timely completion of this study was critical since repair efforts had already started, but the District had major questions of the adequacy of repairs, as well as impacts to the adjacent Middle Island Creek, the downstream Ohio River channel, the scheduled construction by the West Virginia Department of Highways of a new bridge to Middle Island, and on Middle Island, which is owned and managed by the US Fish and Wildlife Service as a National Wildlife Refuge.
FATE OF DREDGED MATERIAL
- Palos Verdes -
CHT assisted ERDC in a field pilot study of in situ capping of contaminated bottom sediments on the Palos Verdes Shelf off the coast of California. CHT’s effort related to the modification and resultant application of the STFATE model for predicting the short-term fate of dredged material released in open water. STFATE was applied to simulate several placement operations that were monitored to assess the ability of STFATE to accurately compute the speed of bottom surges resulting from individual placement operations.
- Columbia River -
CHT assisted the Pacific National Laboratory in a study to assess the impact of dredged material disposal in the Columbia River on bottom dwelling crabs. STFATE was modified to compute the impact pressure force and the spatially and time varying bottom shear stress field resulting from the bottom surge created by the impact of the dredged material with the river bottom. Many scenarios were then run for various water depths and material release times.
- Craney Island Eastward Expansion Project -
This study was conducted for the Virginia Institute of Marine Sciences. The numerical model called SSFATE (Suspended Sediment FATE) was applied to compute suspended sediment plumes resulting from dredging and placement operations that will be required during the Craney Island Eastward expansion project. These include the dredging of a foundation trench for the construction of a wharf, dredging of approach channels that will be required to move the dredge into position to begin dredging the trench, and dredging of the area from the wharf to the Elizabeth River. Since the source strength, i.e. the percent of dredged sediment that will be released into the water column was not known, the approach taken was to make simulations assuming a range of release rates reflecting good to bad dredging practices.
In addition to the dredging scenarios noted above, SSFATE was used to predict the fate of sediment plumes that will be created during the filling of the foundation trench with sand and crushed rock and open water disposal of material dredged from the trench. The final application of SSFATE was to predict the fate of suspended sediment plumes resulting from the effluent that will be discharged at the end of the north containment cell once dredged material starts to be placed in the cell.
FIELD DATA ANALYSIS
- Atchafalaya Bar Channel Fluff Field Study -
CHT assisted the Coastal and Hydraulics Laboratory, ERDC, and USACE District, New Orleans, in the
interpretation of a large and complex field data set collected by ERDC in and around the area where fluff and fluid mud have caused chronic channel maintenance problems. Instrumentation included both fixed ADP and moving ADCP for currents, wave and water-level pressure gauges, water column samplers and profilers, fluid mud and bed samplers, suspended sediment and salinity monitors, and acoustic survey equipment. Data were analyzed to identify factors contributing to the accumulation of fluff in the channel and possible operational, structural and non-structural remedial measures.
- Watershed Modeling and Model Linkages -
Watershed models are used in several ways in regulatory and non-regulatory decision-making and are particularly useful for asking questions about the response of aquatic systems (wetlands, streams and rviers, lakes and reservoirs, and coastal zones) to changed inputs like hydrologic conditions, land use, and contaminant loading. CHT watershed modeling expertise lies in developing both lumped parameter and distruted parameter models. Lumped parameter modeling expertise includes widely used HSPF, SWAT, HEC-HMS and SWMM models. Distributed modeling expertise includes AGNPS, GSSHA and MIKE-SHE. CHT personel have also developed integrated watershed/water body modeling systems capable of simulating the transport and fate of a wide variety of polluntants. These integrated models can be used to assess effects of current and proposed watershed management on changes in contaminant loads delivered to the water bodies, and the effect those changing loads have on water quality and living resources.
- Russian River Watershed Assessment -
Traditionally stream and sub-watershed modeling using HEC-HMS have used a DEM-based terrain analysis approach in a GIS. For the Russian River watershed study, the predefined stream and watershed assessment areas in vector forms were used to develop an HEC-HMS basin model. These areas and stream definitions were developed for use in habitat assessment models. Thus, the hydrologic model had to correspond to those delineations. Results from the HEC-HMS model were used to evaluate potential hydrologic impacts of the Russian River watershed and to provide a basin-wide comparison of hydrologic impacts of alternative conditions, such as changes in system operation and level of development within the watershed. The resulting modeling system links hydrologic simulations with habitat assesments models.
- City of Bremerton's Stormwater System and Surrounding Watersheds -
Sinclair and Dyes Inlets are listed on the EPA 303(d) list of impaired waters because of non-point source pollution from the City of Bremerton, WA and surronding watersheds. A SWMM model was developed to characterized point source and non-point source contributions from surrounding urban areas. HSPF was developed to estimate the non-point source loadings from surrounding natural watersheds. The output results from the SWMM and HSPF modeling served as input to the Sinclair and Dyes Inlet's CH3D/WASP model. The linked watershed and water body model is capable of seamlessly running scenarios to predict types and amounts of pollutants entering the inlets from point and non-point sources and the fate and trasport of those pollutants within the water body.
CHT has a strong reputation for providing technical review of studies conducted by others. Examples include technical reviews for the ERDC on Savannah River modeling conducted by ATM, Inc. and for Versar, Inc. on the “Cumulative Impacts Analysis Report for Uniform National Discharge Standards”. Drs. Johnson and Teeter have served on various Model Evaluation Groups (MEG’s). These include MEG’s for modeling studies in Florida Bay, the Indian River Lagoon in Florida, and in Chesapeake Bay. Dr. Johnson has also served on several panels for the reviews of minimum flow determinations on serveral rivers in the Florida Southwest Water Management District. In addition, CHT Associates have served on many technical review panels. These include Delaware Bay TMDL Study, Gulf of Mexico Hypoxia Study, South Florida Ecosystem Restoration Study, etc.
Computational Hydraulics and Transport LLC. 2006.