Lewis Creek Fish Habitat and Temperature Monitoring Study

This project was supported in part by funding from a Vermont Watershed Grant.

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This stream temperature monitoring project includes several reports and three maps. The maps include: Aquatic Natural Communities Map (4MB),  Natural Resources with Conserved Lands Map (3MB), and a Physical Characteristics (Barriers and Temperature) (2MB) that includes some temperature study results from this study by Lewis Creek Association (LCA), South Mountain Research and Consulting (SMRC), Fish and Wildlife Department (FWD) and Department of Environmental Conservation (DEC). The maps also depict FWD and DEC management approaches, status of protected lands, forest cover and bridge and culvert conditions. A project steering committee designed the fish habitat planning maps for towns, state, landowners and land trusts. The maps were prepared by Kevin Behm at the Addison County Regional Planning Commission.

SMRC managed the temperature study and collected baseline water temperature data in the Lewis Creek watershed using five automatic data loggers that were installed in the river channel at various stations to monitor temperature at 30 minute intervals throughout the summer months of 2011. LCA’s five temperature monitoring stations complemented an existing network of four stations maintained by FWD and one station installed by DEC (see Figure 1). Figure 1

Temperature Study Summary

Along the Lewis Creek main stem, a general warming trend was noted with distance downstream. Lower Watershed stations – Route 7 and Old Hollow – were consistently warmer than Upper Watershed stations – Tatro, Parsonage, and Ballfield – and appeared to track closely with the mean daily air temperature. Groundwater contributions and drainage from forested headwaters, including Hollow Brook and High Knob tributaries, tend to moderate the temperatures in the Upper Watershed. As the Lewis Creek passes west of Route 116, forested buffers become less prevalent in areas that have been cleared for agriculture and development. Unshaded waters are warmed by radiant heat from the sun. Pond Brook tributary also has an apparent warming effect on water temperatures in the Lewis Creek main stem. A large majority of this 14-mile tributary channel has an open canopy. Pond Brook also receives warm water from Bristol Pond which is generally between two and five feet deep.

Mean daily water temperatures for three representative stations are presented in Figure 2. The “Route 7” station is located in the Lower Watershed just upstream from the Route 7 bridge crossing in Ferrisburgh. The “Tyler Bridge” station is located in the Middle Watershed at the Tyler Bridge Road crossing in the northeast corner of Monkton; and the “Tatro” station is located in the Upper Watershed just downstream of the Tatro Bridge crossing in Starksboro. As a general point of reference, the 70°F line has been emphasized on this graph. Temperatures warmer than 70°F are not well tolerated by cold-water fish species such as brook trout. Figure 2

The importance of maintaining forest cover along river corridors is illustrated by Figure 3. This graph presents temperature monitoring data for stations in the Lewis Creek watershed in the summer months of 2010 (yellow squares) and 2011 (white squares). For each station, the plotted value represents the percentage of hours during each summer monitoring period that water temperatures exceeded 70°F. These percentages have been plotted versus upstream distance of each station. Temperatures at the Upper Watershed stations (Ballfield, Parsonage, Tatro, and High Knob) rarely exceeded this threshold; whereas, temperatures in the Lower Watershed stations exceeded 70°F for nearly half of the Summer season. The vicinity of the Tyler Bridge Rd station represents a potential thermal refuge area for cold water fish in the Middle Watershed. Main stem waters are cooled by the Hollow Brook tributary which joins the Lewis Creek just upstream of this station. Temperatures in the Hollow Brook are moderated not only by forest cover in the upper reaches but by groundwater seeps and springs along the lower reaches.

The percent of forest cover in the total upstream watershed at each temperature monitoring station has also been plotted on Figure 3 (green triangles). It is notable that a decrease in forest cover correlates with the warming trend in water temperatures with distance downstream. Figure 3

Forest cover in the watershed is depicted on the  Natural Resources with Conserved Lands Map (3MB).

A more detailed analysis of the temperature monitoring data is provided in a technical memo prepared by South Mountain Research & Consulting (Bristol, VT).

Fish Habitat Management Recommendations

The Lewis Creek watershed is a moderate sized watershed compared to the other major rivers entering Lake Champlain, yet it has 6 of 7 fish, and 9 of 10 macroinvertebrate aquatic natural stream community types found in Vermont. Town and landowner management goals and strategies should recognize this watershed’s unusual biological diversity. According to the State, Lewis Creek aquatic natural communities for fish and macroinvertebrates are in very good to excellent biological condition except for the section from Prison Hollow down to Pond Brook where data indicate slightly degraded biological conditions.

Town, landowner and conservation organization management recommendations:

  • Protect forested areas in headwaters and in "the flats". LC now has ~65% forest cover over all, but some riparian lands are not forested.
  • Restore natural cover connectivity for the length of the creek using Best Management Practices for agriculture, forestry, development and roads. Buffer plans should be informed by geomorphic assessments and have 100ft min on main stem and 50ft min on smaller tribs.
  • Restore or maintain full aquatic organism passage and geomorphic compatibility conditions for all Bridge/Culvert and stream intersections considering Aquatic Natural Community indicator species needs.
  • Be prepared to retrofit or replace as needed for AOP/GC when willing town, state or landowner culverts are up for replacement or where there are scheduled Right of Way upgrades.

Additional Resources for Buffers, Fish Passage and Town Planning:

MAPS

Physical Characteristics (Barriers and Temperature) (2MB)

The Lewis Creek drains 81 square miles of land area located in Addison and Chittenden Counties. At the landscape level, the watershed can be divided into three zones where the main stem has prominent fish barrier bedrock falls. The Upper Watershed is located mostly within the Northern Green Mountain physiographic province, and is composed of the higher-elevation headwaters draining to the States Prison Hollow Road gorge, including the High Knob and Hogback tributaries. The upper reaches of Hollow Brook tributary above a short bedrock falls along Hinesburg Hollow Road are also grouped with the Upper Watershed. The Middle and Lower Watersheds are located within the Champlain Valley physiographic province yet it includes a few high gradient tributaries flowing from Champlain Valley hills. Generally, the Middle Watershed is composed of all those lands draining to the main stem between the States Prison Hollow Road gorge and North Ferrisburgh falls from river mile 23 to river mile 6. This area includes the subwatersheds of Pond Brook tributary and Cedar Brook tributary. The Lower Watershed consists of all those lands draining to the main stem below North Ferrisburgh falls, or the lower 6 miles of the river.

Generally, the Upper, Middle and Lower Watershed zones are identified by Vermont Fish & Wildlife for fisheries management purposes. While the Lewis Creek is regulated as a cold-water fishery (Vermont Water Quality Standards, 2008), the watershed includes a range of cold water, mixed water and warm water fish community types.

There are several additional channel-spanning exposures of bedrock in the Lewis Creek river network. These exposures have been located during stream geomorphic assessments carried out over the last several years, and are depicted on the Physical Characteristics (Barriers and Temperature) (2MB). Depending on a number of factors including stream flow conditions and the species type and age, these bedrock exposures may limit the upstream or downstream movement of fish and other aquatic organisms. According to geomorphic assessment protocols, a “waterfall” is formed by bedrock that extends across the channel and forms a vertical, or near vertical, drop in the channel bed, and “ledge” is bedrock that extends across the channel and forms no noticeable drop in the channel bed, or only a gradual drop in the bed.

Human-constructed features in the watershed, including dams and bridge or culvert crossings, can also prevent the free passage of aquatic organisms, as well as the downstream movement of sediment and large woody debris that are critical components of stream habitat. Culverts are particularly impactful, as they effectively replace the natural stream environment over their length, and can change the hydraulics of channel flow resulting in channel instability local to the crossing. Undersized culverts are generally more likely than bridges to block the downstream passage of woody material and sediment and the upstream passage of wildlife and aquatic organisms.

Dams

On the 42.6 miles of the Lewis Creek main stem and major tributaries that have so far been documented during stream assessments, four dams were identified. One is an earthen dam and driveway for an instream pond on an upper reach of the High Knob tributary in Starksboro; the upstream drainage area is less than 1.5 square miles. Two dams are present at driveway crossings of an upper reach of the Hollow Brook tributary off Lincoln Hill Road in Hinesburg where the upstream drainage area is less than 2 square miles. The fourth dam is Scott Pond Dam on the Lewis Creek main stem along Lewis Creek Road in Charlotte (drainage area of 71 square miles). This concrete dam is founded on bedrock, and operates as a run-of-river structure with a minimal upstream impoundment. At present, the dam is maintained by the US Fish & Wildlife Service and Vermont Fish & Wildlife as a barrier to the upstream migration of sea lamprey, a native species.

Culverts

Culvert encountered on assessed reaches of the Lewis Creek and major tributaries were measured, and their widths are included on the Physical Characteristics (Barriers and Temperature) (2MB) as a percent of the bankfull width of the channel. Percent bankfull width (structure width / bankfull width * 100) is one of several measurements used to determine how compatible the culvert is with the natural channel. It is also a potential indicator of reduced aquatic organism passage (AOP). Ideally, a culvert width should be 100% or more of the channel width, to allow for naturalized flow of water, sediment and woody material, and free passage of aquatic wildlife. Of the twenty culverts measured in the Lewis Creek, all are less than 100% bankfull width. Sixteen of the twenty have a span that is less than 50% of the bankfull width.

Initial screening for geomorphic compatibility (GC) and AOP status has been completed for a limited subset of bridge and culvert structures in the Lewis Creek watershed, including the main stem of the High Knob Brook in Starksboro. Several culverts along VT Route 116 in Starksboro and Hinesburg are being evaluated as part of a transportation project occurring in 2012. A management objective identified during this study is to complete GC and AOP screening for all structures in the Lewis Creek watershed. Towns, state agencies, and landowners can use this screening information to guide prioritization of structures for replacement or retrofitting.

To read more about stream crossings and the importance of maintaining free passage for fish and other aquatic organisms, see the Vermont Stream Crossing Handbook.

Lewis Creek Association Reports:

Details of the dams, instream culverts, and bedrock constrictions located in Lewis Creek can be reviewed in the River Corridor Conservation & Management Plan (South Mountain Research and Consulting, March 2010)

Habitat assessments for select Upper and Middle Watershed reaches of the Lewis Creek are provided in a Lewis Creek habitat assessment report for Starksboro: 'Phase 2 Stream Geomorphic Assessment High Knob Brook Watershed', Milone and McBroom, Inc, February 2009

Aquatic Natural Communities Map (4MB)

Fish are one class of organisms that comprise an interdependent network of plants, animals, and other living creatures. These organisms co-exist and interact in a natural community, governed by ecological processes and the physical environment that surrounds them. The Lewis Creek is recognized state-wide as having a particularly high diversity of aquatic natural community types, due principally to the watershed’s unique variety in topography, geology and vegetation.

The Lewis Creek watershed has seven natural community types that are characterized by distinct fish and macroinvertebrate assemblages, water temperature and channel size and gradient. For more detailed information, see the Lewis Creek Aquatic Natural Communities Map and “Overview of Aquatic Natural Community Occurrences in the Lewis Creek Watershed”, Fiske, Langdon, February 14, 2012.

Town Plan recreation and conservation goals and strategies should aim to help improve habitat conditions for the specific indicator fish species of Lewis Creek’s 7 different community types.

1. Small Cold Water High Gradient Stream Communities Upper Section. Headwaters east of Rte 116, and Prindle (Pease) Brook in M10. Manage for Indicators Fish Species: Brook Trout and Slimy Sculpin.

2. Small - Moderate Mixed Water Low Gradient Stream Communities Upper-Mid Section. Hollow Brook adjacent to Hinesburg Hollow Road, Small N/S trib entering at Prison Hollow Road Manage for Indicator Fish Species: Blacknose Dace, Brook Trout, Common Shiner

3. Mixed Water/Cool High Gradient Stream Communities Mid Section. Below Rt 116 to Pond Brook confluence Manage for Indictor Fish Species: Bluntnose Minnow, Creek Chub, Brook Trout, Blacknose Dace

4. Lake Marsh Outlet Stream Communities Mid Section. Short reaches immediately below Outlets of Monkton Pond & Bristol Pond Manage for Indicator Fish Species: Blacknose Dace, Common Shiner, Brook Trout

5. Small-Moderate Warm Water Low Gradient Stream Communities Mid-Lower Section. Small streams directly entering Lewis Creek from Cedar Pond outlet stream to Lake Champlain Manage for Indicator Fish Species: Creek Chub, Blacknose Dace, Bluntnose Minnow

6. Large Warm Water Moderate Gradient Stream Communities Mid-Lower Section. Below Pond Brook to Rte. 7/Greenbush Manage for Indicator Fish Species: Bluntnose Minnow, Creek Chub

7. Large Warm Water Low-Moderate Gradient Stream Communities Lower Section. Below Fall line, Rte. 7/ Greenbush to Lake Champlain Manage for Indicator Fish Species: Redhorse, Lamprey, Pumpkinseed, Bluntnose Minnow.

Additional Resource:

Langdon, R., et al. 1998. A Classification of the Aquatic Communities of Vermont. The Nature Conservancy and the Vermont Biodiversity Project, Montpelier, VT.

 Natural Resources with Conserved Lands Map (3MB)

Restoration and maintenance of forested buffers along the streambanks is recognized as one of the most important ways to moderate stream temperatures. Land use activities that result in removal of buffers can contribute to warming trends in the river. Forest cover in the Lewis Creek watershed is depicted on the  Natural Resources with Conserved Lands Map (3MB).

This map also displays lands that have been protected from future development through a conservation easement – held either by a land trust (non-governmental agency), state or federal entity. While some easements call for protection of river buffers, wildlife habitat and wetlands, other easements call for protection of agricultural and forestry uses and do not specify river corridor protection.

Hand Painted Fish Illustrations by Vermont Artist

Interested in watershed habitats and the creatures they support? Visit Nick Mayer's Escape Studio to learn more about his scientifically detailed, handpainted watercolor images like the Native Brook Trout below.