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Proposed Lincoln Creek Flood Control

Milwaukee Metropolitan Sewerage District
Butler's Gartersnake Conservation Plan

1. Project Description and Background

Lincoln Creek extends approximately 9 miles within the City of Milwaukee. The creek, which drains a 21-square mile urban watershed, has a history of flooding with flows ranging from less than two (2) cubic feet per second during dry weather to over 3,200 cubic feet per second during storm events. As the Lincoln Creek watershed has developed and urbanized, the quantity of runoff has increased and the quality of the runoff has decreased. In an attempt to reduce flooding, numerous projects were implemented in the past which resulted in channelization of the stream and destruction of habitat. In addition, most of the tributaries to Lincoln Creek have been enclosed or channelized. Approximately 1,600 structures, mostly residential, are located within Lincoln Creek's regulatory floodplain.

The Lincoln Creek Flood Control Management Plan (LCFCMP) proposes the construction of flood control measures which will reduce flooding, improve water quality through abatement of stream bank erosion, and provide habitat for fish, birds, and other wildlife. The flood control plan includes modifying the existing channel, constructing detention basins, cleaning or replacing box culverts, adding bypass culverts, and removing and possibly replacing bridges over the creek. The affected portion of Lincoln Creek runs from 60th Street, north of Good Hope Road, to Green Bay Avenue.

During the review and analysis process of the proposed flood control measures, staff at Havenwoods State Forest (Havenwoods) noted that Butler's gartersnakes (Thamnophis butleri) had been recorded on the property (primarily on the eastern side). This snake is listed as Threatened in Wisconsin and suffers from a variety of threats, most notably the extensive loss of habitat and hybridization with the closely related plains gartersnake (Thamnophis radix). The Butler's gartersnake's range in Wisconsin is believed to be limited to central and northern Milwaukee County and northeastern Waukesha County, with small outlying populations in central Ozaukee County and northwestern Walworth County.

The state endangered species law (s. 29.604, Stats.) prohibits the taking of animal species listed as Endangered or Threatened anywhere that they occur in Wisconsin. The law does allow the Department of Natural Resources (DNR), at its discretion, to authorize the taking of individuals of listed species that otherwise is prohibited by the law if the following conditions apply:

• The taking will not be the purpose of, but will be only incidental to, the carrying out of a lawful activity.
• The party requesting taking authorization will, to the maximum extent practicable, minimize and mitigate the impact caused by the taking.
• The taking will not appreciably reduce the likelihood of the survival or recovery of the endangered species or threatened species within the state, the whole plant-animal community of which it is a part or the habitat that is critical to its existence.
• The benefit to public health, safety or welfare justifies the activity.

In order to determine if Butler's gartersnakes would be affected by the proposed project and if so, how Milwaukee Metropolitan Sewerage District (MMSD) could avoid and minimize impacts to the snake, a herpetological expert (Gary Casper of the Milwaukee Public Museum) was hired to assess and evaluate the snake's status and distribution in the Lincoln Creek area north of Silver Spring Drive. As a result of Mr. Casper's work, MMSD approached the DNR regarding the potential to receive authorization to incidentally take individuals of the Butler's gartersnake population occurring in the area. This Conservation Plan addresses this issue.

2. Butler's Gartersnake Distribution in the Upper Lincoln Creek Area

Mr. Casper both evaluated the existing habitat within the project area north of Silver Spring Drive for suitability to support Butler's gartersnake as well as attempted to determine the presence or absence of the snakes in different parts of the project area. His resulting report, "Environmental assessment for the threatened Butler's gartersnake (Thamnophis butleri) in the upper Lincoln Creek basin, Milwaukee County, Wisconsin. Parts 1&2", describes the current distribution of the Butler's gartersnake in the upper Lincoln Creek area and assesses the value of different types of existing habitat in maintaining a viable population of the snake in the area. The following summary description addresses both the Havenwoods and Green Tree (the land between Green Tree Road and Good Hope Road) sites as well as the connecting riparian corridor.

Havenwoods
Mr. Casper identified a large area within Havenwoods that, based upon its ecological characteristics, constituted good quality habitat ("primary habitat") for Butler's gartersnakes. This area contains a small, created, perched (the area is underlain by approximately five feet of clay) wetland and open pool. It is fed by surface water and as such, the pond typically varies in size from approximately 2-6 acres depending upon precipitation. It is surrounded by a large area of grassland and savanna. In total, this wetland/open grassland/savanna habitat occupies approximately 75 acres and represents the core area supporting Butler's gartersnakes. This primary habitat area appears to support a viable population and likely acts as a emigration source of snakes to surrounding lands. Without this area of primary habitat, it appears unlikely that this population of Butler's gartersnake could survive at Havenwoods or the surrounding lands.

Adjacent to this primary habitat at Havenwoods are more degraded, yet still important, lands that support significant numbers of Butler's gartersnakes. This "secondary habitat" occurs both within the boundaries of Havenwoods and on adjacent lands to the south, west, and north. This secondary habitat consists of old field and savanna natural communities which are degraded to varying degrees by fire suppression (which allows the establishment of significant woody vegetation) and a variety of past, high-intensity land uses on Havenwoods and the surrounding areas.

Green Tree
The area between Green Tree and Good Hope Roads also contains secondary habitat and supports a significant population of Butler's gartersnakes. It is dominated by a mosaic of degraded grasslands, shrub thicket and, along the creek, forested floodplain. The land north of Webster Jr. High School is also used by the snake as secondary habitat - no flood control measures are proposed at this part of the site.

The corridor along Lincoln Creek between the Havenwoods and Green Tree sites is narrow and predominantly mowed as lawn and, as such, does not provide useable habitat. However, it does provide a migration corridor for individuals between these two sites. The movement of individuals between Havenwoods and Green Tree is thought to be critical for maintaining genetic diversity and fitness in the overall population and thus the corridor is likely important for the long-term survival of the snakes in the area.

Mr. Casper concludes that the population of Butler's gartersnakes residing along upper Lincoln Creek is regionally significant in that: (1) it is relatively large, (2) has been little affected by hybridization, and (3) is protected against potential future hybridization given the "sea" of inhabitable, intensively developed land surrounding this "island" Butler's gartersnake population.

3. Proposed Flood Control Measures in the Upper Lincoln Creek Area

At the Havenwoods site, MMSD proposes to move the creek to the east approximately 100 feet, clear some of the woody vegetation along both the old and new creek alignments, cap the landfill on the west side of the creek, and construct an approximately 12 acre detention basin within which would be three small ponds that are designed to permanently hold water.

The actions proposed at the Green Tree site are to remove some of the woody vegetation along the creek, move the creek slightly to the east, cap the landfill in the northwest portion of the site, and construct a detention basin in part of the relatively large, undeveloped upland area. The area where the detention basin is proposed would be re-graded and deepened creating a flat-bottomed depression. Because there is no direct drainage outlet, the bottom of this depression is expected to remain wet or moist except during prolonged dry periods. Although plans have not yet been finalized, the landfill is proposed to be capped potentially using material excavated from the detention basin.

In addition to the work at these two sites, elsewhere in the upper Lincoln Creek area MMSD proposes to clean out or replace box culverts, add bypass culverts, and remove and possibly replace bridges over the creek.

4. Anticipated Impacts of the Proposed Flood Control Measures to the Butler's Gartersnake

Impacts from flooding
There is no evidence, published or known by the DNR, that periodic, short duration (less than 3-4 days) flooding is detrimental to active or hibernating Butler's gartersnakes. In fact, many gartersnakes appear to hibernate in saturated soils. As such, altering the extent and location of flood events in the upper Lincoln Creek area is unlikely in itself to negatively or positively impact this species. Likewise, Butler's gartersnakes occupying detention basins are unlikely to be adversely affected by the flooding these basins are designed to experience.

Impacts to primary habitat
No impact to the primary snake habitat is proposed by the construction of flood control measures and Butler's gartersnake use of this area is not expected to change.

Impacts to secondary habitat
At both Havenwoods and Green Tree, the impacts to secondary habitat will result from one or more of the following: (1) the construction of detention basins, (2) modifying and moving the stream channel, and (3) the capping of landfills.

The detention basins will be unforested, low-sloping depressions (approximately 8-12 feet deep with a 10:1 slope). Apart from the proposed small, permanent ponds within the basin on the Havenwoods property, these areas should hold water for only short periods, typically less than a week, and only during exceptional storm events. As stated above, such flooding is not anticipated to adversely affect the snake. Following construction, it is likely that most, if not all, of the land comprising the detention basins will be utilized by the snakes for basking and foraging. The basins also may provide useable hibernation sites depending upon the habitat conditions that develop over the years.

One potential concern related to the construction of the detention basins is the impact the pollutants settling out of the flood waters will have on the resident snake population. Clearly, much of the area suffers from periodic flooding and pollutant deposition now. By concentrating the flood waters in the detention basins, these areas will accumulate more pollutants than currently is the case. How this will affect the Butler’s gartersnakes is unknown, but is expected to adversely impact their growth and reproduction to some degree.

Currently the Lincoln Creek stream channel is over-grown with woody vegetation in places and does not provide useable habitat. Modifying the stream channel is not expected to adversely impact the Butler’s gartersnake and in fact may benefit the snake where most of the woody vegetation will be removed. In areas where the stream is proposed to be moved, secondary habitat will be converted to non-useable habitat, with the possibility that the existing stream channel could become secondary habitat.

The landfill west of Lincoln Creek adjacent to the Havenwoods property is proposed to be capped. If the new landfill cover is seeded with native vegetation and mowed only later in the fall, then this area will likely be used for foraging and basking by the snakes and will remain as secondary habitat. Plans to cap the landfill northwest of the proposed Green Tree detention basin landfill, which is owned by the Village of Whitefish Bay, are currently being developed but not yet completed.

Mr. Casper estimates that 20-25% of the secondary habitat would be temporarily impacted in the Havenwoods area, with a long-term conversion of approximately 10% of the habitat. Lands comprising this 10% include that portion of the detention basin that is expected to hold water for most of the year and the landfill on the west side of Lincoln Creek that will be re-capped. However, as mentioned above, areas of the detention basin not consistently holding water are expected to be used by the snake for basking and foraging. Further, if the landfill cover is mowed only later in the fall, then this area will also likely be used for foraging and basking. Thus, it is anticipated that the area permanently lost as secondary habitat will be confined to that area that consistently holds water. As a result, the MMSD believes the long-term conversion of secondary habitat is expected to be less than the 10% figure.

At the Green Tree site, Mr. Casper estimates that the construction of the flood retention pond and stream corridor alterations and capping of the landfill are expected to temporarily impact 50% of the secondary habitat, with a long-term conversion of approximately 30%. However, as with the Havenwoods site, it is expected that the snake will re-colonize both the detention basin and the newly capped landfill (if it is mowed only late in the season). At the Green Tree site, the bottom of the detention basin is designed to be moist or wet except during prolonged dry periods. Depending on the habitat conditions that evolve at the bottom of this depression and the amount of pollutant deposition that occurs, some primary habitat may occur here. Thus most, if not all, of the basin is expected to remain as long-term habitat for the snake.

Although not a function of the proposed project, a significant concern for the long-term viability of Butler's gartersnake habitat is vegetation management, or more precisely, the lack of vegetation management. If open, grassy areas currently supporting Butler's gartersnakes are converted to woody vegetation, either by active or passive management, then these areas will become unsuitable for Butler's gartersnakes. As such, without some effort by the owners of lands where Butler's gartersnakes occur to keep existing habitat open and free of most woody vegetation, then the snake habitat (as well as the snake) will, in all probability, be lost in the area.

Construction activities associated with installing a variety of flood control measures are expected to result in the incidental killing ("taking") of Butler's gartersnakes. This taking will be as a consequence of constructing the flood control structures and is not the intent of the proposed project. In response to this potential taking, the MMSD proposes the following measures to minimize adverse impacts to the area's Butler's gartersnake population.

5. Measures Proposed to Minimize Impacts to the Butler's Gartersnake

The MMSD has minimized, or proposes to minimize, adverse impacts resulting from the proposed flood control project to the Butler's gartersnake population occurring in the Lincoln Creek area in the following ways:

• The shape and location of the proposed detention pond at Havenwoods have been altered to avoid the snake's primary habitat and to locate it in the more heavily wooded area currently not utilized by the snake. The detention ponds at Havenwoods and Green Tree are proposed to be the minimum size necessary to alleviate the 1% storm event; smaller sizes may reduce impacts to the Butler's gartersnakes, but would not adequately alleviate flood control problems in the area.
• Ground breaking for construction within the snake's secondary habitat will begin when the weather is sufficiently warm to allow the snakes to move away from disturbance, typically after the first of June. The exact timing of construction will be determined by MMSD and DNR, in consultation with local experts, based on weather conditions.
• At least six weeks prior to construction, snake exclusion fencing (silt fencing trenched into the ground 4-6") will be placed around the construction areas at both the Havenwoods and the Green Tree sites. At this time, if not earlier, at least 20 cover objects will be placed within the enclosed areas. The cover objects will be at least 4 ft² and a combination of either metal or wood materials. The areas under the cover objects will be at least partially cleared of vegetation. Two weeks before construction is to occur, cover objects will be checked 3-5 times/week and all snakes captured will be relocated outside of the construction area (and in the case of the Havenwoods site, into the primary habitat area).
• After construction is completed, the disturbed areas will be planted with native grasses and forbs in a ratio appropriate for the Butler's gartersnake.
• MMSD will keep the property it controls in the upper Lincoln Creek area, to the degree practical and beneficial to the Butler's gartersnake, free of woody vegetation. MMSD will also work with staff at Havenwoods, the Milwaukee Parks Department, Webster Junior High School, and other pertinent landowners to promote vegetation management that enhances the existence and recovery of Butler's gartersnakes in the area. This will include, but is not limited to, clearing select brushy and wooded areas, conducting controlled burns when feasible, mowing grassed areas (e.g. landfill covers) only in the late summer/early fall, and re-vegetating sites using native grasses and forbs.
• MMSD will conduct follow-up monitoring of the Butler's gartersnake population at both the Havenwoods and Green Tree properties. This monitoring will take place 2 and 5 years after the completion of the flood control projects at the Havenwoods and Green Tree properties. Monitoring will include: delineating and describing areas containing primary, secondary, and non-use habitat for the Butler's gartersnake within the construction footprint; evaluating the value of these areas, relative to other lands utilized by the snake outside of the construction area, for their contribution to the survival and recovery of this population; and, using best professional judgment, assessing the short and long-term impacts that the flood control project has had on the population of Butler's gartersnake in the Lincoln Creek area.
• MMSD will allocate $10,000 over a five year period to be used to improve the habitat conditions in the upper Lincoln Creek area for the snake. MMSD will work with the DNR to develop work projects that will be most effective in facilitating the survival and recovery of the species.

6. Alternatives to the Proposed Flood Control Measures

Since 1972, numerous flood control alternatives have been developed and evaluated for Lincoln Creek. A more complete description of alternative approaches to alleviating flooding in Lincoln Creek is provided in the Environmental Analysis completed by DNR. Over time, these alternatives have included a variety of different types of flood water detention facilities, channel modifications, and bridge replacements.

The latest flood control alternatives were developed in 1996 in the LCFCMP and include the following:

• A turf-lined channel combined with an on-line detention facility at Havenwoods.
• Stormwater detention at 11 alternative sites (identified by a technical advisory work group) individually or in combination.
• Flow reduction opportunities at other potential sites.

7. Funding

MMSD estimates that the total cost of the flood control measures in the Lincoln Creek drainage to be approximately $75 million dollars. The cost to minimize impacts to the Butler's gartersnake, including capturing and moving snakes, monitoring, and vegetation management, but excluding actions that would be conducted regardless of the presence of the snake (e.g., re-seeding and silt fencing), is not expected to exceed $25,000. MMSD agrees to, and has the ability to, absorb the costs associated with minimizing the adverse impacts to the Butler's gartersnake.

Copies of the jeopardy assessment and conservation measures are available below or upon request from: