Tools for watershed managers
Session Chair: Rob Dudley, USGS
Session abstracts:
Application of a Distributed-Parameter Watershed Model to the Dennys River Basin to Supporet Characterization of Sub-basin Hydrology
Robert W. Dudley
U.S. Geological Survey, Augusta, ME
The timing and quantity of water moving through the sub-watersheds of the Dennys River Basin and the relative amounts of that water apportioned to surface runoff and groundwater discharge is not well known due to a lack of data. The USGS, in cooperation with the Maine Atlantic Salmon Commission, began a study in 2004 to characterize the quantity, variability, and timing of streamflow in the Dennys River by doing a synoptic summary of historical streamflow data in conjunction with short-term streamflow gages in the Dennys River basin and an application of a distributed-parameter watershed model. The watershed model is a tool that provides the means to characterize sub-watershed hydrology in the Basin and estimate the relative amounts of surface and groundwater contributions to streamflow throughout the watershed. This information will lead to a better understanding of water quantity and quality in the basin that will subsequently support the planning and execution of ongoing and future Atlantic salmon protection efforts.
Stormwater Retrofit Inventories for Maine Impaired Streams
Zach Henderson
Woodard & Curran, Portland, Maine
The Cities of Lewiston and South Portland are developing specific stormwater management plans for the improvement of urban impaired streams. In both cases, the small stream watersheds drain important industrial and commercial growth areas for the cities. The streams are not meeting their intended classification due to urban non-point source pollution and habitat degradation. The probable cause of non-point source pollution and habitat degradation are in part due to directly-connected impervious areas (DCIA).
The MaineDEP, the City of Lewiston and project consultants assembled new and existing GIS and other watershed data in order to develop a comprehensive, specific list of structural and non-structural stormwater solutions for the watershed. In order to develop specific recommendations on the disconnection or treatment of DCIA, the consultant team developed a retrofit inventory strategy that would identify, decentralized structural stormwater management options within the watersheds. Strategy goals were to identify critical subwatersheds that show the most potential for restoration as determined through evaluation of existing in-stream water quality monitoring data, community input and geomorphic conditions. Individual structural retrofit locations were selected in order to minimize impact/modification to existing infrastructure and maximize opportunities for landowners to integrate these relatively low-cost changes during redevelopment or maintenance. Additionally, important community resource areas were identified as a part of the strategy development in order to integrate stormwater management retrofits with future community improvement options, such as community trail development, improved pedestrian access, and open space enhancement.
This presentation will discuss the data needs for development of a stormwater retrofit inventory strategy, strategies used in Maine, the process associated with conducting retrofit inventories, retrofit inventory results from Lewiston, Maine and how these decentralized management systems may be integrated with capital improvement projects, existing programs and community activities.
Comparison of Peak-Flow Estimation Methods for Small Watersheds in Maine
Glenn Hodgkins1, Charles Hebson2, Pamela Lombard1, and Alexander Mann3
1 U.S. Geological Survey, Augusta, ME
2
Maine Department of Transportation, Augusta, ME
3
Maine Department of Transportation, Bangor, ME
Understanding the accuracy of commonly used methods for estimating peak streamflows is important because the design of bridges, culverts, and other river structures are based on these flows. Methods for estimating peak streamflows were analyzed for small watersheds in Maine by the U.S. Geological Survey (USGS) and Maine Department of Transportation (MaineDOT). Modeled peak flows were compared to observed statistical peak flows with return periods of 2, 50, and 100 years for 17 streams in Maine and adjoining parts of New Hampshire with drainage areas of 1.0 to 10 square miles. Peak flows were modeled by the Rational Method, the Natural Resources Conservation Service TR-20 method, USGS regression equations, and the Probabilistic Rational Method. The regression equations were the most accurate method of computing peak flows and the Probabilistic Rational Method was the next most accurate. The Rational Method and particularly the TR-20 method had much larger errors.
USGS and MaineDOT are cooperating on data collection for watersheds with areas less than 1 square mile so that regression equations can be extended to these very small watersheds, but it will be 5 to 10 years before enough data is collected. MaineDOT has used the TR-20 method, the Rational Method, and engineering judgment for estimating peak flows at these very small watersheds in recent years. The research presented here implies that MaineDOT can apply the current regression equations at very small watersheds with some confidence, until the new regression equations are available.
Water Level and Flow Regulation Implementation: Public Water System Implications
Andrews L. Tolman
Maine CDC Drinking Water Program, Augusta, Maine
After more than seven years of discussion, hearings, and stakeholder groups, regulations for water level and flow were adopted by the Legislature and the Board of Environmental Protection in 2007. This process began in the late 1990’s when agricultural withdrawals for irrigation and the conservation of Atlantic salmon came into conflict in Washington County. In reaction to that issue and some instances of Aroostook County irrigation interfering with aquatic habitat, the Legislature directed state agencies to collect water use data.
The collected data indicated that public water systems were the largest single user of water that did not return it to the same water body (paper mills and hydropower use much more water, and generally return it to the same river). As more data accumulated, we identified a number of coastal PWS’s who utilize relatively small lakes and streams to supply seasonally large populations. Their withdrawals result in relatively large fluctuations in water levels and stream flows. These fluctuations exceed the ‘normal’ changes in water level and flow that are envisioned in Chapter 587, the new flow rule. We have been working with DEP for the last several years to balance the needs of PWS’s and their customers with various versions of the proposed rules.
We’re now working with DEP and these water systems to develop a clear picture of their investment in the source, the population served by the system, and the hydrologic and habitat effects of their operation. We will be developing ‘withdrawal certificates’ that allow the water system to continue to serve their customers and identify opportunities to improve habitat as the system changes over time.
