1. USGS PRMS/Modflow Watershed Models
2. UCONN Erosion/ Sediment River Health Indicator Study
3. Bain Habitat Report
4. UMASS Instream Habitat Program Model

Watershed Modeling Overview
Watershed modeling, as illustrated in Figure 5, attempts to understand and quantify complex hydrologic cycle processes within a watershed. These models can be used to estimate how rainfall inputs can be accounted for as infiltration, surface runoff, stream flow, subsurface flow, and evapotranspiration (ET) losses throughout a watershed. Historical climate data (daily precipitation and daily maximum and minimum temperatures and precipitation), historical stream flow data and diversion data are needed for the calibration process of many models. Additionally, the watershed model should be able to account for the heterogeneity of vegetation, soils and land use characteristics in the watershed. The models developed for the Pomperaug Watershed follow these general rules.

1. 1. USGS PRMS/MODFLOW WATERSHED MODELS - Phase I & Phase II completed; Phase III is underway and to be completed 2006.

The overall goal of the modeling is to:

• Characterize and develop a comprehensive understanding of ground water and surface water processes in the watershed.
• Evaluate the effects of specific watershed management scenarios on streamflow in the Pomperaug River through the development and application of a simulation model.
• Provide spatial and temporal hydrologic data sets for use by water-resource managers in decision-making concerning stream habitat, land use, and water use; and as input to stream habitat, geomorphologic, and other hydrologic investigations.

Phases I and II of the Pomperaug watershed modeling effort concluded that the computer model programs PRMS and MODFLOW developed for the watershed will be useful in identifying the seasonal streamflows necessary to protect the chemical, physical, and biological integrity of the river while balancing the use of watershed resources for public drinking water, waste assimilation, and recreational, agricultural and industrial needs.

Phase I work demonstrated:

• The potential importance of groundwater recharge to the stratified drift aquifer in the Pomperaug valley from some upstream tributaries.
• The importance of water releases from the Lockwood-Bronson Reservoir in maintaining the high baseflows in East Spring Hill Brook that sustain well yields in the Nonnewaug well field operated by the Watertown Fire District Water Company.

Phase II work demonstrated:

• That ground water withdrawal (for public water supply) does impact stream flow in our watershed;
• That there is a relationship between the amount of course sediment (aquifer) in a watershed and the amount of water you can expect to get from the aquifer-information that can be used statewide;
• That the amount of effective impervious surfaces in a watershed impacts streamflow-again, information that can be used statewide, though more research is needed.

The last phase of the USGS modeling project will include the finalization and running of management scenarios outlined by the Coalition (Figure 6) using the calibrated PRMS and MODFLOW models. The management scenario simulation runs generated by Phase III will be used by the Coalition and local town governments to evaluate the temporal and spatial hydrologic effects of different water and land use options, so as to facilitate scientifically based watershed management decisions. The information generated in Phase III will also provide hydrologic data sets, maps and reports that will be transferable to other areas in Connecticut.

The USGS will complete the Final Draft USGS Scientific Investigation Report (SIR) that will summarize and document the development and calibration of both runoff models and will also summarize the results of the various scenario simulations. This document will be submitted in 2007 for final USGS review and publication and make the data available for use by the Coalition. USGS has presented the Pomperaug Phase III preliminary study results, as a PowerPoint presentation, to the CT DEP and the Coalition.

2. UCONN EROSION/SEDIMENT RIVER HEALTH INDICATOR STUDY -
This preliminary study of the sediment dynamics of the Pomperaug River will allow the Coalition to relate potential changes in water flows in the watershed to changing conditions in river bottoms, bank erosion and sediment storage. These are all critical habitat elements for fish populations and can affect pollutant transport and storage.

The basic sediment budget, which attempts to quantify the movement of sediment in a river system, will complement the USGS and UMass modeling efforts.

The sediment budget can also provide a valuable basis for formulating watershed management strategies: by indicating the nature and location of the main sediment sources that may need to be controlled; by identifying sediment sinks or areas of sediment storage that may have sediment associated nutrients and contaminants; and by providing a means of assessing the likely impact of upstream control measures on the sediment yield at the watershed outlet. This investigation may also serve to help towns achieve compliance with CT DEP's Stormwater Phase II Programregulations.

Possible Future Tasks::

• Compare the modern condition of the channel to historical conditions.
• Produce a Geographic Information System (GIS) map of erosion and deposition zones within the watershed.
• Establish baseline data sets for future sediment monitoring work.
• Establish a baseline of substrate character (particle size) throughout the watershed.
• Present a map of erosion and deposition zones to all appropriate land use commissions and make the map available on the Coalition's website.
• Present map of erosion and deposition zones to town public works departments for discussion of planning road-sanding/vacuuming schedules. This task may also provide CT DEP Stormwater Phase II Management Program compliance opportunities.

Results to date:

• A Power Point presentation, fact sheet and report on historical conditions were delivered to the PRWC Board in spring 2004.
• Field trip highlighting sediment process in the Pomperaug River held by Melinda Daniels, UCONN on October 9, 2005
• For summary report of work to date, click here.

3. BAIN HABITAT REPORT - Completed

• the physical habitat quality of the stream;
• the chemical environment and general water quality of the stream;
• the native stream and riparian communities;
• spatial relations (stream connectivity);
• temporal patterns (annual flow regime).

The project:

• Organized existing data and identify existing data gaps;
• Established current biological status of fish populations throughout the Pomperaug River watershed and its tributaries;
• Collected new physical habitat data such as bankfull width, depth and cross-sectional area; substrate characterization; drainage area of each of the sub-drainage basins; amounts of forest cover and impervious surfaces in each sub-drainage basin; survey-level hydrologic simulation models (e.g. run-off, nutrient loads) using GIS data; and a hydrograph for the watershed;
• Collected flow data during high flows and base flows from each of the sample sites, covering a range of stream sizes through each of the seven regional drainage basins.

Deliverables received by the Coalition include cumulative size/frequency distributions of substrate particles from 16 study areas in the watershed, and population estimates of fish (number/kilometer of stream length) caught in 1991 and 2001 at 16 watershed sites, indicating species and, for some species, densities. The detailed report is available on the Coalition's library.

4. UMASS INSTREAM HABITAT PROGRAM MODEL - Completed-2006
To help understand the relationship between streamflows and the availability of fisheries habitat (habitat potential), the Coalition contracted with Dr. Piotr Parasiewicz of the University of Massachusetts (formerly of Cornell University) to develop a Meso¹ Habitat Simulator(MesoHABSIM) model for the river.

MesoHABSIM is a river habitat model that attempts to address the need for managing large-scale habitats and river systems. It models larger river reaches, or meso-habitats, such as riffles, runs, and pools. The physical characteristics of each meso-habitat are measured and compared to fish habitat preference curves to determine the amount of useable fish habitat at different river stages, or water levels. For a more complete discussion of this model go to www.neihp.org/mesohabsim/

As with other stream habitat models, the variation in the spatial distribution and amount of Meso-habitats can provide key information on habitat quality changes corresponding to alterations in streamflow, channel changes, and stream improvement measures. It provides a solid base for quantitative assessment and simulation of habitat conditions for the whole stream.

The objective of the Pomperaug habitat modeling effort is to develop instream and watershed scale information required for designing a management plan that best serves the needs of the aquatic resources of the watershed.

• Finished mapping representative sites.
• Defined habitat criteria for species and life stages different from those of the resident adult fish.
• Built a habitat model based on target fish community and physical and biological data.
• Simulated habitat baseline conditions.
• Conducted a time series analysis to investigate the level of habitat availability necessary at different seasons and set up seasonally variable flow targets. Created seasonal flow targets defining the band of minimum, critical and optimum conditions.
• Evaluated model predictions, taking into account fish observations.
• Defined prediction accuracy, deficits and needs for improvement.
• Made recommendations.

A final report and MesoHABSIM Training for all interested stakeholders will be completed in late 2006.

For a PowerPoint presentation of results to date, click here