The Demand Report features three water-demand scenarios by major user sectors and for geographical areas that encom-pass groundwater withdrawal points and surface water intakes in the 11-county water planning area of northeastern Illinois.
The three scenarios represent water withdrawals under current demand conditions and reflecting recent trends in develop-ment (CT scenario), a less-resource intensive scenario (LRI), and a MRI scenario. Table 5, reproduced from the Demand Report, features the factors affecting future water demand along with the scenario assumptions made for modeling future water de-mand. Scenarios were extended to the planning horizon, 2050.
Only the LRI scenario is predicated on the sort of potential intervention represented by this regional water plan. The CT and MRI scenarios will largely occur in response to a combina-tion of a continuacombina-tion of historical trends and future economic conditions. The LRI scenario is different from the CT scenario across eight of 11 factors that affect water demand, but in only two factors of eight that are potentially affected by this plan:
water conservation and future water prices.94
Scenarios do not account for the needs of aquatic ecosystems or other in-stream uses. The reader is referred to the Demand Report for details concerning methods used, model perfor-mance, uncertainties, and other information regarding the study. Here we will focus on the scenario outcomes.
Figure 8 illustrates modeled demand from 2005 to 2050 across the three scenarios (excluding once-through flow power).
A rather striking feature of Figure 8 is that only with active intervention (i.e., LRI scenario) might the region keep overall water demand relatively flat (7.24% growth over 45 years) while population increases as much as 38%. Maintaining the status quo in northeastern Illinois could result in an increase in water demand from 36% under the CT scenario to 64% under the MRI scenario; either could happen absent a commitment to ongoing formal planning and implementation of the current and future regional water plans.
94 The distribution of population growth factor did not prove to be useful in the model due to the aggregate nature of public water supply sector data (i.e., water utilities sell water to both residential customers as well as commercial and industrial customers.) Additional analysis will uncouple residential from commercial/industrial accounts within public water-utility sales to determine the effects on total water withdrawals that would result from geographically different patterns of population growth within the water planning region.
Chapter 2 | Framework for Regional Water Supply Planning and Management
Table 5: Assumptions for factors affecting future water demands in the 11-county area of northeastern Illinois
Factor Scenario 1
Current Trends (CT) or Baseline Scenario 2
Less Resource Intensive (LRI) Scenario 3
More Resource Intensive (MRI)
Total population CMAP projections CMAP projections CMAP projections
Distribution of population
of growth CMAP projections More population in Cook and
DuPage counties More population in Kane, Kendall and McHenry counties
Mix of commercial/industrial
activities Current trends Decrease in high water-using activities Increase in high water-using activities Median household income Existing projections of 0.7%/year
growth Existing projections of 0.5 %/year
growth Higher growth of 1.0 %/year
Demand for electricity 9.61 kWh/capita + 0.56% annual
growth 9.61 kWh/capita without growth 9.61 kWh/capita + 0.56% annual growth
Power generation No new plants within study area, 3 units retired
No new power plants within study area, 3 units retired, 2 plants convert to closed-loop cooling
Two new power plants in study area with closed-loop cooling
Water conservation Continuation of historical trend 50% higher rate than historical trend No extension of historical trend Future water prices Recent increasing trend (0.9%/year)
will continue Higher future price increases (2.5%/
year) Prices held at 2005 level in real terms
Irrigated land Constant cropland, increasing golf
courses (10/decade) Decreasing cropland + no increase in
golf courses Constant cropland increasing golf courses (20/decade)
Livestock Baseline USDA growth rates Baseline USDA growth rates Baseline USDA growth rates Weather (air temperature
and precipitation) 30-year normal (1971-2000) 30-year normal (1971-2000) 30-year normal (1971-2000) Source: Dziegielewski and Chowdhury, 2008
Figures 9-11 illustrate demand by the three major sources of water: Lake Michigan, groundwater, and inland rivers. Begin-ning with Figure 9, demand for Lake Michigan water under the LRI scenario could shrink despite a larger projected population.
This, of course, means that per capita use in 2050 will have decreased as compared to the base year of 2005 should an LRI-like scenario occur.
Figure 9 also shows that under the CT scenario, Lake Michigan water demand could grow 20% by 2050 to 1,223 MGD. This amount is very close to the amount of water cur-rently allocated by IDNR through 2030 (1,210 mgd). The MRI scenario for Lake Michigan indicates potential demand of 1,397 MGD at 2050, a 37% increase from 2005. The MRI scenario demand amount, however, is 27% greater than the average of 1,099 MGD diverted for domestic pumpage over the period of 1981-2006.
Table 6 provides a theoretical breakdown of the Illinois diversion for 2050 using the MRI scenario value for domestic pumpage and average or actual values for other diversion components taken from the IDNR OWR Lake Michigan Man-agement Section.95 Considering the MRI scenario, the highest water-demand scenario of three demand scenarios studied, relative to other diversion components is useful for exploring the potential of the diversion limit to accommodate a plausible future (2050) beyond the date for which lake-water allocations are currently set (2030).
The MRI scenario for public water supply, as a component of the Illinois diversion, indicates maximal use of the allowable diversion of 2.1 billion gallons per day (3,200 cfs) at 2050.
As noted by IDNR, following the year 2020, Illinois’ 40-year run-ning average diversion must always remain below 3,200 cfs.
The U.S. Supreme Court Decree makes no allowance for Illinois
to have a water debt after that year. It is important, therefore, that steps be taken now to build a positive Lake Michigan wa-ter bank account as a hedge against climate change impacts, excessive leakage, and accommodation of new requests for Lake Michigan water.
The greatest potential to accommodate an increase in domes-tic pumpage lies with a reduction of the stormwater-runoff component of the diversion. This is a reminder of the need to holistically manage the various aspects of the hydrologic cycle, land use, and water demand.
Demand will grow under any of the three scenarios for ground-water dependent communities, as is illustrated in Figure 10. Conservation and efficiency measures, along with other demand-management practices, will have to be aggressively pursued if the desideratum is to either keep demand relatively flat or reduce overall demand while population is projected to grow dramatically in counties that rely heavily or exclusively on groundwater. Other supply/source alternatives to groundwater may exist if needed, but it is beyond the scope of this study to offer more than simple acknowledgment of such.
Figure 11 shows current and modeled demand from the region’s two inland surface water sources: Fox River and Kankakee River. Demand could grow regardless of what level of intervention occurs, but the ISWS has determined that for the Fox River, new river withdrawals could provide an additional 40 to 45 mgd, cost of new infrastructure to deliver this new water notwithstanding. This potential is based on increased groundwater withdrawals for public supply and subsequent discharge to the river as effluent.96 The amount of new river-water expected to become available could change should a greater percentage of wastewater be reused or land applied rather than discharged into the Fox River.
95 Ibid. 17.
96 Vernon Knapp, Illinois State Water Survey, presentation titled “Effects of Future Water Demands and Climate Change on Fox River Water Avail-ability” at http://www.sws.uiuc.edu/iswsdocs/wsp/ppt/FoxScenarios.pdf October, 2008.
Chapter 2 | Framework for Regional Water Supply Planning and Management
Table 6: Theoretical breakdown of Illinois diversion in 2050 Diversion Component Amount of Water (mgd)
Domestic Pumpage (MRI) 1,397
Stormwater Runoff 546
Discretionary 66
Lockage 58
Leakage 24
Navigation Makeup 23
Total Diversion 2,114
The value for stormwater runoff represents the average from 1984-2003; the current discretionary allocation 177 MGD for MWRDGC, will be lowered to 66 MGD in 2015;
the lockage value represents a 25-yr average (1980-2005); average leakage and navigation-makeup values are unavailable, the amounts used are from water year 2005 which may or may not be a representative year. 2,114 MGD = 3,221 cfs
Figure 9: Public supply, Lake Michigan withdrawals, 2005 vs. 2050 scenarios, in million gallons per day
Figure 10: Public supply, groundwater withdrawals, 2005 vs. 2050 scenarios, in million gallons per day
Figure 11: Public supply, Fox and Kankakee River
withdrawals, 2005 vs. 2050 scenarios, in million gallons per day Public Supply, Groundwater Withdrawals:
2005 vs. 2050 Scenarios, in millions of gallons per day
0 50 100 150 200 250 300 350 400
2005 Less resource
intensive Current trends More resource intensive Source: Dziegielewski and Chowdhury, 2008
Public Supply, Fox and Kankakee Rivers Withdrawals:
2005 vs. 2050 Scenarios, in millions of gallons per day
0 10 20 30 40 50 60
2005 Less resource
intensive Current trends More resource intensive Source: Dziegielewski and Chowdhury, 2008
Source: Dziegielewski and Chowdhury, 2008 2005 Less resource
intensive Current trends More resource intensive 0
200 400 600 800 1,000 1,200
Public Supply, Lake Michigan Withdrawals:
2005 vs. 2050 Scenarios, in millions of gallons per day