town of vernon · pz-2010-17: proposed amendment to section 4.25 of the zoning regulations 4...

OFFICE OF THE

TOWN PLANNER

14 PARK PLACE, VERNON, CT 06066-3291 Tel: (860) 870-3667 Fax: (860) 870-3683

E-mail: [email protected]

TOWN OF VERNON

MEMORANDUM

TO: Planning and Zoning Commission FROM: Leonard K. Tundermann, AICP, Town Planner SUBJECT: PZ-2010-17: Proposed Amendments to Section 4.25 of the Zoning Regulations DATE: October 5, 2010 Environmental Considerations Statements have been made about the sensitivity of the PDZ Exit 67 zone to deleterious impacts of development on the wetlands that feed the upper reaches of the Tankerhoosen River watershed. Statements and data contained in the Tankerhoosen River Watershed Management Plan support this contention. The executive summary of the plan states in part,

Development pressure in this headwaters region at the Exit 67 interchange in Vernon poses a major threat to the long-term health of the watershed. Further stresses on the headwaters have been created by development of an industrial park in Tolland through which a key headwater stream flows, as well as the presence of the highway itself, which continues to generate increasing traffic loads from development alon the I-84 corridor. (pg ES-1)

Section 2.8 of the plan describes land use and land cover within the subwatersheds of the Tankerhoosen River watershed. A salient measure of watershed health is impervious cover.

The correlation between watershed impervious cover and stream indicators is due to the relationship between impervious cover and stormwater runoff, since streams and receiving water bodies are directly influenced by stormwater quantity and quality. …research as generally shown that when impervious cover in a watershed reaches between 10 and 25 percent, ecological stress becomes apparent. Between 25 and 60 percent, stream stability is reduced, habitat is lost, water quality becomes degraded, and biological diversity decreases (NRDC, 1999) (pg. 43)

PZ-2010-17: Proposed Amendment to Section 4.25 of the Zoning Regulations 2 October 5, 2010

Approximately two-thirds of the PDZ Exit 67 zone falls within the Walker Reservoir subwatershed, and about one-third falls within the Clarks Brook subwatershed. A delineation of the Walker Reservoir subwatershed is enclosed. The Walker Reservoir subwatershed is estimated at 19.90% impervious cover, and the Clarks Brook subwatershed at 17.20%. (pg 44) The overall imperviousness of the Tankerhoosen River watershed is estimated at approximately 9.7%. The figure below shows percent impervious cover in all the subwatersheds of the Tankerhoosen River watershed.


A watershed buildout analysis was performed based on identification of areas presently undeveloped or underdeveloped. The watershed buildout analysis was used in conjunction with the existing conditions impervious cover analysis to estimate future impervious cover in the Tankerhoosen River subwatersheds. On the basis of estimated new development and redevelopment, impervious cover in the Walker Reservoir subwatershed is predicted to increase from 19.90% to 29.13%, and the Clarks Brook subwatershed is predicted to increase from 17.20% to 20.60%. Section 2.10 of the watershed management plan provides a comparative subwatershed analysis to identify the subwatersheds with the greatest vulnerability and restoration potential.

Table 2-26. Results of Subwatershed Vulnerability Analysis

Subwatershed

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Bolton Notch Pond 2 10 6 1 7 2 3 3 0 5 0 41 Clarks Brook 3 10 6 4 7 2 5 5 1 4 0 47 Gages Brook 3 5 6 6 11 4 6 6 3 5 0 55 Gages Brook South Tributary 2 5 6 4 1 5 6 5 3 5 0 42 Lower Tankerhoosen River 7 10 0 7 2 5 4 5 7 5 0 53 Middle Tankerhoosen River 3 10 2 2 2 2 4 5 3 3 3 38 Railroad Brook 2 0 6 12 0 6 9 0 5 1 0 40 Tucker Brook 2 0 6 2 0 3 5 6 3 2 0 28 Upper Tankerhoosen River 0 0 4 2 0 4 8 3 3 3 0 27 Walker Reservoir 9 10 4 4 2 3 2 5 10 6 0 56 As shown in Table 2-26, the following subwatersheds are considered most vulnerable to future development impacts and should be given highest priority for conservation efforts to maintain existing resource conditions:

Clarks Brook, Gages Brook, Gages Brook South Tributary, Lower Tankerhoosen River, Walker Reservoir.


Table 2-28. Results of Subwatershed Restoration Potential Analysis

Subwatershed

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Bolton Notch Pond 1 1 1 5 3 10 0 6 6 0 5 0 38 Clarks Brook 1 10 5 7 8 10 0 4 11 1 4 0 60 Gages Brook 5 12 6 5 8 4 10 3 12 3 5 6 79 Gages Brook South Tributary 5 3 0 3 3 1 14 2 9 3 5 9 57 Lower Tankerhoosen River 1 6 1 5 1 1 15 5 11 7 5 6 64 Middle Tankerhoosen River 5 6 1 5 6 10 5 5 10 5 3 0 61 Railroad Brook 10 0 0 1 6 1 9 0 0 5 1 0 34 Tucker Brook 10 10 0 5 6 7 11 4 11 1 2 0 66 Upper Tankerhoosen River 10 3 0 1 7 4 12 1 6 3 3 3 52 Walker Reservoir 1 10 1 7 4 1 0 7 9 10 6 0 55

As shown in Table 2-28, the following subwatersheds should be given highest priority for restoration potential to improve upon existing conditions:

Clarks Brook, Gages Brook, Lower Tankerhoosen River, Middle Tankerhoosen River, Tucker Brook.

Based on the combined results of the subwatershed vulnerability and restoration potential analyses, the following subwatersheds were recommended for detailed assessment and planning:

Clarks Brook, Gages Brook, Gages Brook South Tributary, Lower Tankerhoosen River, Middle Tankerhoosen River, Tucker Brook, Walker Reservoir.


Having noted these watershed assessments, several points should be kept in mind.

1. Wetlands: The northeastern end of the PDZ Exit 67 zone lies at the upper end of the Walker Reservoir subwatershed. That portion of the zone contains the bulk of the wetlands. A GIS plot is attached showing the PDZ Exit 67 zone and the wetlands in the zone and in proximity. Again, about one-third of the zone at the southeastern end lies in the upper end of the Clarks Brook subwatershed. Removing the wetlands from the zone’s development potential would lead to a substantial portion of site development falling within the Clark’s Brook subwatershed. The wetlands themselves, discounting a small pocket of wetlands along the zone’s western boundary, are part of a wetlands system that are found to the southeast of Hartford Turnpike, include wetlands around Exit 67, and continue along Reservoir Road in the direction of Walker Reservoir. Obviously the wetlands are an important natural resource and perform important ecological functions within the watershed. Some of those functions, as documented in the attached document downloaded from DEP’s website, include nutrient retention, sediment trapping, and pollution filtration. Appendix G. to DEP’s outdoor recreation plan elaborates on those functions:

Water Purification: Wetlands aid in the purification of surface and ground water. They have a “self cleaning” ability which, if not overtaxed, can filter or process pollutants from runoff before they enter an aquifer or an adjoining watercourse. In many respects, wetlands function much like sophisticated sewage treatment plants by removing nutrients and other pollutants prior to discharge to a waterway of the ground. Nutrient and Sediment Trapping: In addition to being pollution fighters, wetlands are able to trap sediments resulting from natural and man-induced erosion. However, increased development along many of the state’s watercourses can hinder the wetlands’ capability to trap these sediments. Often special measures need to be taken to decrease the sediment runoff in urbanizing areas.

Sensitive design of any proposed development would seem achievable in a manner that preserves the capacity of the wetlands to perform their numerous functions.

2. Impervious Cover: Whereas the Walker Reservoir subwatershed is already close to 20% impervious cover and is ranked the highest in vulnerability to future development impacts, much of the PDZ Exit 67 zone within that subwatershed is wetlands that are not likely to be converted to impervious cover. Another factor that may mitigate the effects of additional impervious cover is the application of Low Impact Development (LID) measures in site and building design. Table 6-9 in the Tankerhoosen River Watershed

I 84

EXIT 67

SOUTH ST

RESERVOIR RD

HARTFORD TPKE

REED ST

MT VERNON DR

MILE HILL RD

FORE

ST DR

FOX HILL DR

GREEN RD

WHITE ST

S GROVE ST

CROWN ST

H ENR Y PA RK WAY

HALE ST EXTDOBBS CROSSING

SUNRISE DR

LOEHR RD

I 84

I 84

EXIT 67

PDZ-Exit 67 AreaAnd Vicinity

0 500 1,000250Feet

ÜLegend

Lot LinesBuildingsPavementBridgesWater CoursesRedesignated Wetlands


Management Plan suggests that existing conditions in the Walker Reservoir subwatershed produce 52.6 tons/year of sediment loads and that future buildout without LID controls will generate 65.6 tons/year. Alternatively, future buildout with LID controls is expected to generate 58.0 tons/year of sediment loads, a reduction of 11.1% percent from the buildout maximum. The application of LID measures could have a significant impact in reducing runoff from a development within the zone. As it is, common practice in handling runoff from development is to have a zero increase from pre-development site conditions.

In summary, it would appear that the environmental sensitivity of the Walker Reservoir subwatershed and the Clarks Brook subwatershed can be protected from degradation from future development in the PDZ Exit 67 zone. Minimizing the increase in impervious cover through use of LID measures and preserving the functions of the wetlands through site design could ameliorate the long-term threat to the Tankerhoosen River and watershed from development pressures.

FUNCTIONS AND VALUES OF WETLANDS • Ecological Integrity • Wildlife Habitat • Finfish Habitat • Nutrient Retention,

Sediment Trapping, and Pollution Filtration

• Flood Control • Shoreline Anchoring and

Dissipation of Erosive Forces

• Groundwater Use Potential • Agricultural Potential • Forestry Potential • Visual and Esthetic Quality • Educational Potential • Water Based Recreation • Noteworthiness

Wetlands are among the most highly productive plant communities. The most valuable wetlands are those that are intact, diverse in habitat, and buffered from human activity. Wetlands are essential habitat for a large number of wetland species, particularly amphibians, waterfowl and wading birds. Streamside vegetation provides shade, which lowers water temperatures necessary for certain fish species, as well as refuge. Wetlands remove and store levels of sediment and nutrients which might otherwise damage the aquatic ecosystem. Wetlands reduce flood damage by acting as storage basins. Wetlands act as a buffer zone between watercourses and uplands reducing shoreline erosion and the accompanying sediment deposition within watercourses. Some wetlands recharge the water table and have a purifying effect on water discharged downstream. Floodplain wetlands contain nutrient rich soils. Through proper management, many wetlands have a potential for production of forest products. Wetlands are often areas of scenic beauty providing wildlife viewing opportunities. Wetland areas can be an important tool for teaching ecological principles. Many streams, lakes and other wetland areas are canoeable and provide abundant fishing and viewing opportunities. Many wetlands possess features - such as important historical or archaeological sites, unique geographical features, and endangered species - which give them a high value regardless of any other attribute.

http://www.ct.gov/dep/lib/dep/water_inland/wetlands/seg1_functional_values.pdf

town of vernon · pz-2010-17: proposed amendment to section 4.25 of the zoning regulations 4...

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