Stress Analysis

Detailed resource stress analyses have been conducted to identify where and when important resources in McHenry County may face pressures from urbanization.  The “stress” natural, agricultural, and cultural resources face from future development can be measured from the likelihood of development occurring within their boundaries, based on the probability values projected in LEAM. Using this approach, we can differentiate between impacts of different land-use patterns on resource areas. One land-use pattern might have less of an impact on wetlands when compared to another, but may also have more of an impact on prime farmland and aquifer recharge zones. In comparing different future land-use scenarios, tradeoffs may have to be made based on the impacts on different resources.

To quantify this stress on resources from development, there is an assessment of the likelihood that development will occur where these resources are located relative to the rest of the region, relative to other resource region, and compared to the development probabilities in other scenarios.  In LEAM, the probability that any one 30m x 30m piece of land (or cell) will developed is computed for all the development scenarios.  For a given scenario, the cells that make up any given resource area will thus possess a range of probability values.  The 90^th percentile of these values is used as an index to represent the probability range.  The 90^th percentile, the value that has 90% of cells with less development probability,  is used because it gives a sense of both the maximum value and the range of probabilities.

The maps in this impact analysis section illustrate the spatial consequences of the development patterns projected to occur, according to the policy interventions that define each scenario, for various environmental and social resources in McHenry County.  For each scenario, Advanced Identification wetlands, Chicago Wilderness Green Infrastructure areas, Illinois Natural Areas Inventory areas, High school districts, watersheds, and critical groundwater protection areas are analysed to determine what level of development stress they will be under based on LEAM spatial results.  Grey areas indicate an insignificant amount of stress, meaning little to no development pressure projected during between 2006 and 2030; dark green indicates some development pressure; light green and orange represent increasing levels of development pressure; and red indicates a significant and critical amount of developement pressure threatening the integrity, or carrying capacity in the case of high school districts, of the resource in question.

As stated above, some areas or resources may be stressed in one scenario and not in another.  It is also possible, yet maybe counter-intuitive, for a resource area to be surrounded by development yet not significantly stressed.  This phenomenon occurs when the resource in question is either protected or simply not as attractive to development according to the policy interventions and/or constraints which define a particular scenario.  More explanation and resource stress highlights are included in the details section below the map in each stress analysis folder. 

Sample Analysis (McHenry County)

Development Stress on ADID Areas
This analysis measures development stress placed on streams, rivers, and lakes designated as Advance Identification (ADID) high quality habitats. ADID is a US-EPA planning process used to identify wetlands and other waters that are either suitable or not for the discharge of dredged and fill material. 

These ADID high quality habitat areas also function as automatic triggers under the McHenry County Conservation Design Ordinance. 

The criteria for determining the value as habitat include:

• Presence of State threatened or endangered species,
• Designation as a natural area on Illinois Department of Conservation’s Illinois Natural Areas Inventory,
• Presence of high quality wildlife habitat,
• Presence of high quality plant communities,
• Presence of stream or stream segment of high biological value.*

 Development stress on ADID wetland areas is a result of existing development and the spatial reallocation of growth according to development constraints imposed by their boundaries.  The Green Infrastructure scenario offers a good example of how resource stress changes according to the different policy interventions.  Compared to the Reference scenario, significantly more ADID wetlands throughout McHenry County exist under stress due to the combination of existing and new development occurring adjacent to their boundaries. 

Development Stress on Groundwater Recharge Areas
This analysis assesses development stress affecting groundwater recharge areas in McHenry County as defined in the McHenry County Groundwater Management Plan.   The map layer identifies the locations of three particular data layers based on the Plan:  soils with excessive permeability potential; class III groundwater recharge areas; and areas with a high potential for aquifer contamination.  The aforementioned layers were combined to identify the areas containing all characteristics.

Development stress on groundwater recharge areas is a result of existing development and the spatial reallocation of growth according to their boundaries.  In the Groundwater Protection scenario, a great deal of the groundwater recharge areas are under high levels of stress.  This is most likely the result of existing development  and new development occurring immediately adjacent to the protected areas due to development constraints imposed to protect critical groundwater resources.