LEARNING & EXPLORING

ORV Detail - Watershed Hydrology

Additional Watershed Hydrology Documents

Watershed Hydrology Report - PDF from Management Plan Appendices.

The following text is an excerpt from the Watershed Management Plan Chapter VI.

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1. The Importance of Watershed Hydrology

Watershed hydrology describes the journey of water through a watershed system. The processes that move water through the system such as precipitation, evapotranspiration, groundwater infiltration and surface water flow all have significant effects on overall ecosystem health.

Instream flow, the amount of surface water flowing in a river or stream at any given time, has been called the “master variable” in a river system. Instream flow affects a multitude of river ecosystem functions including aquatic life and its related habitat, nutrient cycling, sediment transport, water temperature, river bank stability, groundwater recharge, and a host of other features. Water from river and groundwater sources also plays an important role in sustaining human health by providing drinking water, agricultural irrigation, fire protection, recreational opportunities and wastewater assimilation of discharges from septic treatment and other sources. The ability to balance instream needs with out-of-stream uses is a difficult challenge endemic to the whole country, and certainly Southern New England and Connecticut. Unlike many watersheds in Connecticut today the Eightmile River Watershed is not relied upon as a major source of public or industrial water supply, nor is it impacted by large point source discharges from wastewater treatment plants or industrial sources. As such, the Eightmile River Watershed is in a unique position sustaining an intact hydrologic system.

River flow can be influenced in a number of ways, including: (1) diversions of water out of the river by either direct withdrawals or groundwater wells; (2) alteration of flow from dams; (3) discharges of effluent into the river from treatment plants, industrial sources and stormwater pipes; and (4) influence of impervious cover, such as roadways, parking lots and roof tops, that both generate stormwater runoff and interrupt the important connection between surface water and groundwater critical to maintaining a natural flow regime.

Consideration of these influences in the Eightmile River Watershed finds:
No substantial affect from water diversions. Currently only one consumptive groundwater diversion exists.
No dams are currently regulating flow.
There are no direct point source discharges from industrial sources or wastewater treatment plants and therefore no impacts to hydrology.
The Eightmile River Watershed has very low levels of impervious cover, currently at 3% of the total watershed area, minimizing the negative affects caused by stormwater runoff and interruption of groundwater infiltration.
Land cover in the Eightmile River Watershed is a combination of high levels of forest cover coupled with low levels of developed area. The recovery of the forests and wetland systems of the watershed are allowing for the stabilization of low flow patterns, reflecting a system in ecosystem recovery from an intense agrarian past.

Combining all these factors it is apparent the Eightmile River Watershed hydrologic regime is operating without major impediments or influences and as such is a naturally functioning system. It is rare in Connecticut, especially along the coast, to have a watershed system of this size with a natural intact flow regime in place. As such the Eightmile River Watershed can be considered a unique example of how a natural hydrologic system in Connecticut functions and is considered an outstanding resource value based on such exemplary characteristics.

A full report on Watershed Hydrology as an outstanding resource value can be found in Appendix 2 – Outstanding Resource Value Report Watershed Hydrology.

2. How Watershed Hydrology is Threatened

An assessment of watershed hydrology threats in the Eightmile River Watershed identified 18 potential activities that could cause hydrologic conditions to degrade. The greatest threats identified come from the possible impacts of increases in impervious surfaces and in turn stormwater runoff. Increased levels of impervious surface can cause increases to the velocity, frequency, volume and duration of stormwater runoff ultimately impacting natural flow regimes. As well, impervious surfaces can cause a loss of natural groundwater infiltration capacity preventing the replenishment of groundwater aquifers. Groundwater is a key contributor to instream flow in New England rivers and streams, especially in low-flow summer conditions. A loss of groundwater may cause lower flows for longer durations, especially in the driest times of the year. In addition, the potential for new or expanded surface and groundwater diversions for irrigation needs on golf courses, recreational fields, or agricultural fields was also identified as a significant threat.

The complete threat analysis can be found in Appendix 7 – Analysis of Existing Protections and Potential Gaps in Protection and Appendix 8 – Summary of Analysis of Management Issues and Threats to outstanding Resource Values.

3. Existing Protections and Gaps

In order to understand potential additional protection needs for watershed hydrology a comprehensive review was completed of current protection measures planned and implemented at the local, state and federal level.

Some of the key existing protections for watershed hydrology at the local, state and federal level include:
East Haddam uses the most current Best Management Practices (BMP’s) for the design and installation of new stormwater management systems by following the Connecticut Dept. of Environmental Protection Stormwater Quality Manual.
Local inland wetland commissions have the authority to regulate water diversions of any size.
The State of Connecticut regulates all diversions of water over 50,000 gallons per day.
Open space protection at the local level is keeping large tracts of forest land intact, and preventing new imperviousness or stormwater runoff from occurring.
Inland Wetland regulations in all three towns focus on minimizing impacts to wetlands and watercourses.

A number of potential additional tools have been identified that could further advance the protection and enhancement of watershed hydrology. These additional tools are discussed below in Section F.

Two summaries of existing protection are available in the appendices. One is a comprehensive review of municipal regulations and related plans for East Haddam, Lyme and Salem (Appendix 12 – Municipal Regulation and Policy Review) and the second is a summary of local, state and federal protections specific to each threat category (Appendix 7 – Analysis of Existing Protections and Potential Gaps in Protection).

Gaps in protection were identified as a result of comparing known watershed hydrology threats with existing protection measures. Primary gaps in protecting watershed hydrology include:
Limited ability to manage impervious surface levels
State water quality classifications do not provide a standard for instream flow.
Agricultural impoundments are exempt from local inland wetland regulations
It is not clear whether existing dams within the watershed are required to operate as run-of-river operations.
Water diversions grandfathered by the state are not reviewed or regulated regarding potential environmental impact.
There is currently a lack of necessary scientific data to adequately assess the potential impacts of existing or new surface or groundwater withdrawals.
Gravel extraction regulations in each community do not address hydrologic impacts of potential graveling operations.
It is difficult to asses or manage the cumulative affects of timber harvesting on watershed hydrology.
Local Inland Wetland Commissions have not historically regulated the impacts of surface or groundwater withdrawal activities.

4. Watershed Hydrology Protection Goal

The watershed hydrology goal for the Eightmile River Watershed is to understand, enhance and protect the surface and groundwater hydrology of the Eightmile River Watershed in order to maintain a natural hydrologic condition in the Watershed.

5) Watershed Hydrology Indicators

a. Impervious Cover
b. Dams and Flow Manipulation
c. Surface or Ground Water Diversions
d. Riparian Corridor condition
e. Watershed Forest & Vegetative Cover
f. Aquifer Storage and Recharge
g. Natural Stream Flow and Ground Water Level Conditions
h. Intact Natural Processes