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Chequamegon-‐Nicolet National Forest Watershed Vulnerability Assessment, Eastern Region (R9) Figure 14. Relative vulnerability of groundwater recharge to climate change for HUC-6 watersheds on Chequamegon-Nicolet NF Runoff from the groundwater watersheds is dominated by groundwater discharge and they were considered to have low vulnerability. There were 50 HUC-6s classified as groundwater runoff. They were located predominantly in outwash sands on Lakewood/Laona RD, northern Eagle River/Florence RD, and western Great Divide RD. The estimated average annual future and historic potential groundwater recharge for these watersheds was 10.1 and 9.4 inches, resulting in an average increase of 0.7 inches (Table 4). These watersheds are most likely to provide refugia for groundwater-dependent resources such as brook trout and other cold water stream fish. They may be an area to focus adaptive management for these resources. Runoff from mixed watersheds includes a combination of groundwater and surface water and these watersheds were considered to have moderate vulnerability. There were 59 mixed HUC-6s located on Park Falls units, eastern Great Divide RD, and Eagle River/Florence RD. The estimated average annual future and historic potential groundwater recharge for these watersheds was 8.6 and 8.1 inches, resulting in an average increase of 0.6 inches (Table 4). Some of these watersheds may have a few cold water streams in local areas where soil and topography provide adequate groundwater recharge and discharge and these streams may be vulnerable yet important potential refugia. Runoff from surface watersheds is dominated by surface runoff processes and these watersheds were considered to be most vulnerable. There were 37 watersheds classified as surface runoff; 30 were 252 Assessing the Vulnerability of Watersheds to Climate Change
Chequamegon-‐Nicolet National Forest Watershed Vulnerability Assessment, Eastern Region (R9) complete HUC-6s and seven were split watersheds. These were located in the moraines on the Medford unit, the clay plain along Lake Superior, the southern half of Park Falls unit, southwest portion of Eagle River/Florence RD, and central portion of Great Divide RD. The estimated average annual future and historic potential groundwater recharge for these watersheds was 7.0 and 6.6 inches, resulting in an average increase of 0.4 inches (Table 4). With a few exceptions, these watersheds will contain very few surface waters that are substantially fed by groundwater and these will be the most susceptible to climate change impacts. The exceptions are the split watersheds on the Bayfield Peninsula, which have low groundwater recharge themselves but many of whose main streams are heavily fed by groundwater from upslope groundwater recharge watersheds and an occasional isolated coldwater stream. Infrastructure While it is not possible at this time to predict changes in flood frequency and magnitude due to climate change, the WICCI downscaled projections provide sufficient evidence that the frequency and intensity of large precipitation events will increase and are likely to increase floods. The WICCI Stormwater Working Group reported that more frequent and severe flooding in rural areas are likely from the projected increases in rainfall and shifting precipitation patterns that favor more rain during periods of low evapotranspiration and high soil moisture which result in lower infiltration rates (Potter et al. 2010). Maintaining the current infrastructure, minimizing natural resource impacts, and reducing life cycle maintenance costs will logically require road crossing designs that will last at least 75 and preferably 100 years. Structures installed in the near future must last until the late 21 st century and survive future climate changes. The CNNF 2004 Forest Plan revision included a guideline that all road and trail stream crossings be designed to pass the 100-yr flood (USDA Forest Service 2004). Since 2004, the CNNF has attempted to design all crossings to pass the 100-year flood with the headwater-to-depth (HW/D) ratio of less than 1 (i.e., water level below the top of the culvert) to prevent pressurized flow or surcharging in the structure and to provide freeboard. In 2008, the US Forest Service published a guide for simulating stream channels at road and trail stream crossings to maintain or restore ecological connectivity (USDA Forest Service 2008). This design procedure also maximizes structure life and minimizes maintenance requirements. Using this guide, a structure width is selected that will allow the construction of a channel with bankfull width and stable banks, and a structure height is selected that will prevent pressurized flow and maintain sediment transport. In recent years, the CNNF has used two procedures to design road and trail stream crossings: no-slope with tailwater control, and stream simulation. Both procedures consider bankfull width and pass the 100yr flood with HW/D
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AUTHORS AND CONTRIBUTORS Authors* M
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ASSESSSING THE VULNERABILITY OF WAT
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staff; the task group included repr
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Figure 2. Conceptual model for asse
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Figure 3. Density of springs and sm
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Using Historic Data One finding con
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NF (Region 8) relied on information
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level of uncertainty. Though there
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climate (Casola et al. 2005). Only
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sensitivity. Most were derived from
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The sensitivity evaluation typicall
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in exposure. The result of combinin
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highest priority for management act
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to information affected the assessm
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with and rely on in many resource d
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Pilot National Forest Reports Conte
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Assessment of Watershed Vulnerabili
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Gallatin National Forest Watershed
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Helena National Forest Watershed Vu
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Grand Mesa, Uncompahgre and Gunniso
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White River National Forest Watersh
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Coconino National Forest Watershed
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Sawtooth National Forest Watershed
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Shasta Trinity National Forest Wate
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Chugach National Forest Watershed V
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Chugach National Forest Watershed V
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