Hydrology

Major Waterways

Champaign County waterways can be perennial, where water is consistently flowing year-round, or intermittent, where water only flows at certain times of the year (EPA, 2013). Major waterways include the Sangamon River, Kaskaskia River, Embarras River, Salt Fork River split, and the Middle Fork River.

Impacts to waterways, both perennial and intermittent, can pose serious challenges planners need to consider. Direct impacts of transportation projects include pollution and habitat destruction from road construction and maintenance actions, like dredging and chemical/debris runoff from impervious surfaces. Indirect impacts, such as stream bank alteration, can disrupt flooding patterns, resulting in more severe and unpredictable flood events. Additionally, expansion of transportation systems often means more automobiles on the road, resulting in more air pollutants that degrade water quality.

In general, planners should avoid development around waterways whenever possible. However, if avoidance alternatives prove to not be reasonable, feasible, prudent, or practicable (NEPA litmus test for acceptable alternatives), then several regulatory issues require consideration:

• A Section 404 permit must be obtained from the U.S. Army Corp of Engineers before discharging into waters of the United States.
• A Creekway Permit is required for all new construction within the Boneyard Creek District to ensure development does not increase flooding risks or impact cultural, economic, and environmental quality of the creek for the city.
• The Champaign County Storm Water Management and Erosion Control Ordinance Section 6 lists local requirements for protecting existing drainage and water resources that new projects must adhere to.
• General NEPA and IDOT procedures require that alternatives to potential adverse impacts to waterways be considered and adopted, when practicable.

Flood Hazard Areas

Floodplains are the lowland and relatively flat areas adjoining waterways subject to a one percent or greater chance of flooding in a given year. They absorb and moderate the flow of significant amounts of water from flooding events in adjacent waterways. Two categories of floodplains exist based on the percent annual chance of flooding (IDNR, 2001):

• 100-Year Floodplain: Also known as the “base floodplain,” this is the area subject to a one percent annual chance of flooding (1-in-100). Potential project sites within these areas will have issues with flooding. Insurance for such projects will be costlier, and steps must be taken to avoid negative impacts
• 500-Year Floodplain: Appearing on the fringes of the 100-year floodplain, this is the area subject to a 0.2 percent chance of flooding each year (1-in-500). While development is less limited than the 100-year floodplain, flooding issues within the 500-year floodplain are not uncommon.

When projects encroach on the floodplain, either longitudinal or transverse, the floodplain function is altered, often leading to increased flood damages, unpredictability in future flooding events, and habitat loss. Planners should avoid floodplain development whenever possible and should be aware of the following guidelines:

• Executive Order 11988: Floodplain Management requires that alternatives to potential adverse impacts to floodplains be considered and adopted, when practicable.
• The Champaign County Special Flood Hazard Areas Ordinance lists rules and guidelines concerning development in and around floodplains, including the Floodplain Development Permit that must be acquired before any person, firm, corporation, or governmental body not exempted by law before beginning development within the floodplain.
• Creekway Permit: all new construction within the Boneyard Creek District must have this permit to ensure development does not increase flooding risks or impact cultural, economic, and environmental quality of the creek for the city.

Biologically Diverse Streams

In Champaign County 31 stream segments are considered Biologically Diverse Streams (BDS). This designation is part of the Biologically Significant Stream designation developed by the Illinois Department of Natural Resources (IDNR) and denotes streams of uniquely high biodiversity. The BDS designation uses fish, macroinvertebrate (including sensitive populations), mussel, crayfish, and threatened and endangered species data. The primary variable of a BDS is species richness, or the number of different species represented in an ecological community. Streams are graded A-E in terms of individual diversity scores and the distribution of diversity scores found throughout an area, with A being the highest diversity grade possible. These streams are located throughout the County, with the northwest portion of the County having the highest rated stream segments, along the Sangamon River.

IDNR uses these stream ratings as the basis for resource protection and implementation of the Illinois Wildlife Action Plan. Planners should use BDS ratings as a mechanism for identifying high-quality stream communities and guiding planning decisions. When developing project alternatives, protection of these streams should be prioritized.

Watersheds

Watersheds are the area of land that drains to one body of water. They affect the quality of the body of water they surround, as well as provide a host of ecosystem services including nutrient cycling, carbon storage, erosion/flood control, and water filtration (EPA, 2020).

Watersheds are identified by their hydrological unit code (HUC), separating watersheds into six classes devised by the U.S. Geological Survey. The HUC describes the way smaller watersheds drain areas that together form larger watersheds (EPA, 2020).

Generally, watersheds are named for the waterbody into which they drain. Five major watersheds (HUC-8) are found within Champaign County: Upper Sangamon, Upper Kaskaskia, Vermilion-Wabash, Embarras, and Middle Wabash-Little Vermilion.

Transportation infrastructure should be developed within the context of regional management goals for natural resources and the environment. Controlling and managing land use is an important tool to preserving watershed health and meeting LRTP goals. Planners should review current zoning and/or projected future land use to determine if a specific development project fits within regional goals. Planners also need to consider the impacts: (direct/indirect; short/long term) to development within watersheds. Examples of these impacts include impervious cover, drainage patterns, and habitat loss. The effect is to shift development away from the stream and other water resources most impacted by development and toward areas with lesser impact. Some basic watershed planning goals that can guide project development include flood control, meeting state water quality standards/designated use, wildlife habitat enhancement, and greenway establishment

Wetlands

IDOT defines wetlands as those areas that have hydric soils, inundation or saturation by surface or groundwater, and prevalence of hydrophytic vegetation (IDOT, 2019). Wetlands provide a host of ecosystem services crucial to economic, social, and ecological well-being. Their continued function is dependent upon planning efforts to reduce encroachment and minimize impacts from transportation planning. The American Planning Association Policy Guide on Wetlands states that the best way to protect wetlands is to identify them in plans and develop alternatives to avoid adverse impacts. To implement this guidance, use the Interactive Map, in conjunction with the REF Strategies.

Champaign County has experienced a 40 to 60 percent loss in wetlands due to agricultural draining and land conversion since the 1800s. The remaining wetlands have been seriously fragmented. Wetland protections require early incorporation into planning such as:

• Section 404 permit: must be obtained from the U.S. Army Corp of Engineers before discharging into waters of the United States, including wetlands.
• Interagency Wetlands Policy Act: With the goal of “no net loss” of wetlands throughout the state, IDNR has specific requirements on wetland compensation plans through mitigation banking.

Water Quality

Every two years, the Illinois EPA publishes a report on the quality of Illinois surface and groundwater resources, the Illinois Integrated Water Quality Report. Scientists determine water quality based on the ability of a waterway to support several designated uses. Waters not supporting any one of their designated uses are deemed impaired and listed on the IEPA 303(d) List. The 303(d) List inventories impaired streams, describes the causes and sources of impairment, and gives priority rankings for strategies to meet water quality standards. Priority rankings determine how urgently IEPA needs to set pollutant reduction goals. Each pollutant receives a target reduction, known as a Total Maximum Daily Load (TMDL). TMDLs determine permitting requirements for pollutant discharge into waterways. Approval times vary based on priority, but once listed on 303(d), a stream segment must have a TMDL developed for it within 8-15 years. The majority of Champaign County streams on the 303(d) List are of “moderate” priority, meaning TMDL development will be closer to the 15-year mark.

Currently, only three impaired stream segments in Champaign County have approved TMDLs:

• Salt Fork Vermilion River (IL_BPJ-07)
• Saline Branch Drainage Ditch (IL_BPJC-08)
• Boneyard Creek (IL_BPJC-08)

Regardless of whether or not a TMDL has been established for a listed stream in a project area, it is prudent for planners to check if the associated watershed has an approved TMDL. Impacts to one segment have effects on another, and segments should not be viewed as isolated systems. Current Illinois TMDL reports can be found here.

Champaign County waterways are evaluated for four designated uses: Aquatic Life, Fish Consumption, Primary Contact (recreation), and Aesthetic Quality. Due to limited resources, only about 15 percent of Illinois stream miles are assessed for at least one designated use each reporting cycle. Just over 40 percent of Champaign County waterways were assessed in the 2018 Water Quality Report (575 miles out of 1,309). Of those assessed, 148 miles have been listed on the 303(d) List, covering 12 stream segments across the County.

As with all other resources, best practice is to avoid any impacts by locating projects and alternatives away from vulnerable areas. This may not always be possible, however. Planners need to know the status of potentially impacted waterways in a project area. Answering the following questions, through use of REF and IEPA resources, will result in fewer impacts and a more streamlined environmental review/permitting process:

• Is the waterway 303(d) Listed? If so, has a TMDL been established?
• What are the limitations of the TMDL?
• What causes and sources of impairment apply to this waterway?
• How can further impairment be reduced, or quality improved with this project?

Mahomet Aquifer

At 3,700 sq. miles, the Mahomet Aquifer is one of the largest sand/gravel aquifers in the state. The aquifer supplies 509,000 people across 14 counties with clean drinking water and is directly fed by the Sangamon River (CCRPC, 2010). The quality of the Sangamon River and those waterways connected to the Sangamon all have an influence on what ends up in the Mahomet Aquifer. Thus, Champaign County streams impact the drinking water for most of the County.

The Mahomet Aquifer is designated as a Sole Source Aquifer (SSA) by the EPA. As an SSA, it supplies at least 50 percent of the drinking water for its service area, and there are no reasonably available alternative drinking water sources should the aquifer become contaminated. This designation means that the EPA conducts a separate review for projects 1) located within the area overlaying the Aquifer and 2) receiving federal funding. If a project has the potential to contaminate the Aquifer, then the EPA will require modifications or federal funding can be denied.

Planners should be aware of the increasing stress put on the Aquifer by urbanization. Transportation projects should prioritize minimizing water usage and potential contaminants from entering both streams and aquifer wells.