watervulnerability
watervulnerability
watervulnerability
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Chequamegon-‐Nicolet National Forest Watershed Vulnerability Assessment, Eastern Region (R9)<br />
Culvert sizing criteria were obtained from the CNNF Forest Plan (USDA Forest Service 2004) and<br />
Stream Simulation (USDA Forest Service 2008) guidelines. The results of hydraulic modeling for a select<br />
number of recent culvert replacements on the CNNF were reviewed and compared to the culvert sizing<br />
criteria. These included several sites with low to moderate runoff potential and one with high runoff<br />
potential.<br />
The number of road-stream crossings and their density (#/sq mi) within the CNNF boundary were<br />
determined from an inventory conducted by the CNNF. The watersheds were placed into one of four<br />
classes based on road-stream crossing density. Runoff potential was estimated from hydrologic soil<br />
groups. Watersheds were placed into one of four classes based on their average HSG rating.<br />
The vulnerability of individual HUC-6s to increased flood flows and failure of culvert infrastructure was<br />
estimated by combining the road-stream crossing density and runoff potential classes. The ratings for<br />
these two parameters were combined to classify the vulnerability of each HUC-6 as either very low, low,<br />
moderate, or high. In this classification, HSG ratings were given twice the weight of crossing density<br />
ratings because HUC-6s with high runoff potential were expected to experience higher increases in flow,<br />
making infrastructure in those watersheds more vulnerable than watersheds with low runoff potential,<br />
regardless of the crossing density.<br />
Stream Fishes<br />
The analysis included two primary steps: (1) evaluating statewide modeling of the potential impacts of<br />
climate warming on stream fish distributions at the Forest level, and (2) summarizing those results to<br />
characterize the vulnerability of cold and cool-transitional stream fishes to climate change at the<br />
watershed scale.<br />
Lyons et al. (2010) analyzed the potential effects of climate change on water temperature and 50 stream<br />
fishes in Wisconsin. They utilized habitat models developed from the Wisconsin aquatic gap program to<br />
estimate existing and future distributions of each fish. These models were applied to 86,898 km of stream<br />
(at the 1:100,000 scale) in Wisconsin under four different climate scenarios, including current conditions,<br />
minor warming (summer air temperature increases 1 °C and water 0.8 o C), moderate warming (air 3 o C<br />
and water 2.4 o C) and major warming (air 5 o C and water 4.0 o C). The water temperature increase of<br />
0.8 o C for each 1.0 o C increase in air temperature used in their study was an oversimplification<br />
necessitated by the statewide study that did not take into account how groundwater input, land uses, or<br />
changes in flow might alter the response of streams to air temperature increases.<br />
For the CNNF analysis, the GIS layers of predicted fish distributions developed by Lyons et al. (2010)<br />
were obtained for 15 fish species from the Wisconsin Department of Natural Resources (WDNR) and<br />
USGS. The selected species included 2 cold water fishes (brook trout and mottled sculpin), 8 cool or<br />
transitional water fishes (blacknose dace, brook stickleback, creek chub, longnose dace, northern<br />
hogsucker, northern redbelly dace, walleye, white sucker) and 5 warm water fishes (black crappie,<br />
hornyhead chub, logperch, smallmouth bass, and stonecat). The distributions for each climate scenario<br />
and species were intersected with CNNF HUC-6 delineations. The amount of predicted habitat for the<br />
current climate and moderate warming was determined for each species by HUC-6 and for all HUC-6s<br />
combined. One additional cold water species, brown trout, was modeled but not carried through the<br />
analysis.<br />
The vulnerability of individual HUC-6s was estimated by determining the percentage change in habitat<br />
for each species in the watershed. That percentage was based on the total habitat for all HUC-6s for that<br />
species. Within each HUC-6, cold and cool water species were combined by calculating a simple<br />
arithmetic average. Each HUC-6 was then classified according to its vulnerability to climate change<br />
239 Assessing the Vulnerability of Watersheds to Climate Change