The deep bedrock aquifer system in northeastern Illinois is encountered at depths ranging from about 200 feet in areas of central northern Illinois to an average of about 1,000 feet below land surface at Chicago. The aquifers have a collective thickness of 300 to 1,300 feet in the Chicago region, averaging 700 feet. They are composed chiefly of sandstones and dolomites, although most of the water is derived from the sandstone units. Pumpage from deep bedrock wells for public and self-supplied industrial supplies in the Chicago region increased from 200,000 gallons per day (gpd) in 1864 to a peak withdrawal of 182.9 million gallons per day (mgd) in 1979. Between 1991 and 1994, pumpage decreased from 112.7 mgd to 67.1 mgd, mostly due to a shift to Lake Michigan water, particularly in DuPage County. As a result, water levels in deep wells rose between 1991 and 1995, particularly in southern Lake, eastern DuPage, and western Cook Counties. Average annual water-level rises during the four-year period varied from one foot in Kendall County to 38 feet in DuPage County and averaged about 14 feet. This marked the first time that average water-level changes were upward in all eight counties of the Chicago area since detailed record-keeping began in the 1950s.
This report summarizes extensive studies of the water resources of northeastern Illinois. This 3700-hundred square mile metropolitan-industrial area includes Cook, DuPage, Kane, McHenry, Lake and Will Counties with a population of seven million persons.Water shortages, depending on resource use schemes, may approach 200 million gallons by the year 2000. Possibilities for meeting these needs are described as a guide to allocation of Lake Michigan water and future planning for water resources.
The Champaign County Forest Preserve District (CCFPD) applied for and received a grant to conduct a diagnostic-feasibility study on Homer Lake commencing in April 1997. Homer Lake is an 83-acre public lake within the Salt Fork River Forest Preserve in Champaign County, Illinois. The lake is located in the Second Principle Meridian, Township 19N, Range 14W, Section 31; it is 3 miles northwest of the town of Homer. Homer Lake has a maximum depth of 19 feet, a mean depth of 7.4 feet, a shoreline length of .3 miles, and an average retention time of 0.097 years. The Homer Lake watershed, including the lake surface area, is 9,280 acres. The two inflow tributaries are Conkey Branch and the west branch (unnamed). The diagnostic study was designed to delineate the existing lake conditions, to examine the cases of degradation, if any, and to identify and quantity the sources of plant nutrients and any other pollutants flowing into the lake. On the basis of the findings of the diagnostic study, water quality goals were established for the lake. Alternative management techniques were then evaluated in relation to the established goals.
The Illinois State Water Survey (ISWS), under contract to the Imperial Valley Water Authority (IVWA), has operated a network of rain gauges in Mason and Tazewell Counties since August 1992. The ISWS also established a network of groundwater observation wells in the Mason-Tazewell area in 1994. These networks are located in the most heavily irrigated region of the state. The region's major source of water for irrigation, municipal, and domestic water supplies is groundwater pumped from thick sand-and-gravel deposits associated with the confluence of two major ancient river valleys, the Mississippi and the Mahomet-Teays. Relatively recent extreme weather events (e.g., the drought of 1988 and the great flood of 1993) resulted in large fluctuations in groundwater levels in the Imperial Valley area. The purpose of the rain gauge network and the groundwater observation well network is to collect long-term data to determine the rate of groundwater drawdown in dry periods and during the growing season, and the rate at which the aquifer recharges. This report presents data accumulated from the rain gauge and observation well networks since their inception through August 2000. Precipitation is recorded continuously at 20 rain gauges for each storm that traverses the Imperial Valley. Groundwater levels at the 13 observation wells are measured the first of each month. The database from these networks consists of eight years of precipitation data and six years of groundwater observations. At the beginning of groundwater observations in late 1994, the water levels were at their highest in the six years of observation. These high groundwater levels were the result of the very wet 1992-1995 period when annual precipitation was above the 30-year normals at both Havana and Mason City. From September 1995-August 1997, precipitation in the region was well below the 30-year normal followed by the 1997-1998 and 1998-1999 observation years with rainfall totals that were slightly above and slightly below normal, respectively. Groundwater levels in the observation wells reflected the multi-year rainfall patterns, showing a general downward trend during the dry years, a recovery in the wet 1997-1998 year, and a leveling off in 1998-1999. Precipitation in the region during observation year 1999-2000 was well below normal, mirroring the quite low totals observed during the dry years of 1995-1997. In response, groundwater levels fell to levels similar to those experienced in 1996-1997. Analysis indicates that groundwater levels are affected by both the precipitation in the Imperial Valley area and, for wells close to the Illinois River, by river stage. Generally, water levels in wells follow antecedent precipitation and Illinois River stage by one to two months, i.e., June groundwater levels are most highly correlated with the Illinois River stage or precipitation that occurs in April or May. The analyses conducted indicate the need for continued operation of both networks due to inconsistencies associated with groundwater levels, precipitation, and the Illinois River stage. For instance, although observation well number 2 (MTOW-2) is located near the center of Mason County, well away from the Illinois River, it has an equal correlation with the Illinois River stage and area precipitation. Additional data collection and analyses are needed to determine the reasons for this and other data disparities.
A dense raingage network has operated in Cook County since the fall of 1989, to provide accurate precipitation for use in simulating runoff for Lake Michigan diversion accounting. This report describes the network design, the operations and maintenance procedures, the data reduction and quality control methodology, a comparison of rainfall amounts obtained via analog chart and data logger, and an analysis of precipitation for Water Year 2001 (October 2000 - September 2001). The data analyses include 1) monthly and Water Year 2001 amounts at all sites, 2) Water Year 2001 amounts in comparison to patterns from network Water Years 1990-2000, and 3) the 12-year network precipitation average for Water Years 1990-2001. Also included are raingage site descriptions, instructions for raingage technicians, documentation of raingage maintenance, and documentation of high storm totals.
Flooding, upland soil and streambank erosion, sedimentation, and contamination of drinking water from agricultural chemicals (nutrients and pesticides/herbicides) are critical environmental problems in Illinois. Upland soil erosion causes loss of fertile soil, streambank erosion causes loss of valuable riparian lands, and both contribute large quantities of sediment (soil and rock particles) in the water flowing through streams and rivers, which causes turbidity in sensitive biological resource areas and fills water supply and recreational lakes and reservoirs. Most of these physical damages occur during severe storm and flood events. Eroded soil and sediment also carry chemicals that pollute water bodies and stream/reservoir beds. Court Creek and its 97-square-mile watershed in Knox County, Illinois, experience problems with flooding and excessive streambank erosion. Several fish kills reported in the streams of this watershed were due to agricultural pollution. Because of these problems, the Court Creek watershed was selected as one of the pilot watersheds in the Illinois multi-agency Pilot Watershed Program (PWP). The watershed is located in environmentally sensitive areas of the Illinois River basin; therefore, it is also part of the Illinois Conservation Reserve Enhancement Program (CREP). Understanding and addressing the complex watershed processes of hydrology, soil erosion, transport of sediment and contaminants, and associated problems have been a century old challenge for scientists and engineers. Mathematical computer models simulating these processes are becoming inexpensive tools to analyze these complex processes, understand the problems, and find solutions through land-use changes and best management practices (BMPs). Effects of land-use changes and BMPs are analyzed by incorporating these into the model inputs. The models help in evaluating and selecting from alternative land-use and BMP scenarios that may help reduce damaging effects of flooding, soil and streambank erosion, sedimentation (sediment deposition), and contamination to the drinking water supplies and other valuable water resources. A computer model of the Court Creek watershed is under development at the Illinois State Water Survey (ISWS) using the Dynamic Watershed Simulation Model (DWSM) to help achieve the restoration goals set in the Illinois PWP and CREP by directing restoration programs in the selection and placement of BMPs. The current study is part of this effort. The DWSM uses physically based governing equations to simulate propagation of flood waves, entrainment and transport of sediment, and commonly used agricultural chemicals for agricultural and rural watersheds. The model has three major components: (1) hydrology, (2) soil erosion and sediment transport, and (3) nutrient and pesticide transport. The hydrologic model of the Court Creek watershed was developed using the hydrologic component of the DWSM, which is the basic (foundation) component simulating rainfall-runoff on overland areas, and propagation of flood waves through an overland-stream-reservoir network of the watershed. A new routine was introduced into the model to allow simulation of spatially varying rainfall events associated mainly with moving storms and localized thunderstorms. The model was calibrated and verified using three rainfall-runoff events monitored by the ISWS. The calibration and verification runs demonstrated that the model was representative of the Court Creek watershed by simulating major hydrologic processes and generating hydrographs with characteristics similar to the observed hydrographs at the monitoring stations. Therefore, model performance was promising considering watershed size, complexities of the processes being simulated, limitations of available data for model inputs, and model limitations. The model provides an inexpensive tool for preliminary investigations of the watershed for illustrating the major hydrologic processes and their dynamic interactions within the watershed, and for solving some of the associated problems using alternative land use and BMPs, evaluated through incorporating these into the model inputs. The model was used to compare flow predictions based on spatially distributed and average rainfall inputs and no difference was found because of a fairly uniform rainfall pattern for the simulated storm. However, the routine will be useful for simulating moving storms and localized thunderstorms. A test to examine effects of different watershed subdivisions with overland and channel segments found no difference in model predictions. This was because of the dynamic routing schemes in the model where dynamic behaviors were preserved irrespective of the sizes and lengths of the divided segments. Although finer subdivision does not add accuracy to the outflows, it allows investigations of spatially distributed runoff characteristics and distinguishes these among smaller areas, which helps in prioritizing areas for proper attention and restoration. The calibrated and verified model was used to simulate four synthetic (design) storms to analyze and understand the major dynamic processes in the watershed. Detailed summaries of results from these model runs are presented. These summary results were used to rank overland segments based on unit-width peak flows, which indicated potential flow strengths that may damage the landscape, and were based on runoff volumes that indicate potential flood-causing runoff amounts. Stream channel and reservoir segments also were ranked based on peak flows and indicate potential for damages to the streams. Maps were generated showing these runoff potentials of overland areas. These results may be useful in identifying and selecting critical overland areas and stream channels for implementation of necessary BMPs to control damaging effects of runoff water. The model also was used to evaluate and quantify effects of the two major lakes in the watershed in reducing downstream flood flows and demonstrating model ability to evaluate detention basins. The model was run for one of the design storms with and without the lakes. The results showed significant reduction of peak flows and delaying of their occurrences immediately downstream. These effects become less pronounced further downstream. This report presents and discusses results from the above applications of the DWSM hydrology to the Court Creek watershed along with descriptions of the watershed, formulations of the hydrology component of the DWSM, limitations of the model and available data affecting predictions, and recommendations for future work. Efforts are currently under way at the ISWS to add subsurface and tile flow routines to the DWSM that would improve model predictions and their correspondence with observed data. It is recommended that stream cross-sectional measurements be made at representative sections of all major streams in the Court Creek watershed and that stream flow monitoring be continued or established at least at outlets of major tributaries and upper and lower Court Creek. A minimum of four equally spaced raingage stations are recommended for recording continuous rainfall.
The hydrologic regime of a natural stream is usually highly complex and encompasses a wide range of discharges. The magnitudes and frequencies at which the various discharges occur play a key role in creating the channel's morphology. The concept of 'dominant discharge' proposes that there exists a single steady discharge that, theoretically, if constantly maintained in a stream over a long period of time would form and maintain the same basic stable channel dimensions as those produced by the long-term natural hydrograph. This theoretical discharge is referred to as a stream's dominant discharge. If such a dominant discharge exists and can be accurately calculated, this discharge can be one of the tools that stream restoration personnel use to help design channels that are morphologically stable, i.e., not experiencing either excessive erosion or sediment deposition. There is no direct method to calculate a stream's dominant discharge, and stream researchers have commonly assumed that the dominant discharge can be equated with either the stream's bankfull discharge, a specific flood recurrence interval, or the stream's effective discharge. The purpose of this study is to analyze the available data and existing computational methods for the third approach, that being the estimation of effective discharges specific to Illinois streams. The effective discharge of a stream is defined as the single discharge rate that carries the most sediment over time. Note that the effective discharge is not typically a discharge associated with the most extreme flood events, which may carry large amounts of sediment load but occur infrequently. Instead it is commonly considered to be a moderately high discharge having a more modest load, but occurring frequently enough that in the long-run it carries more sediment than the extreme flood events. To facilitate computations, the effective discharge is estimated as occurring within a discharge class or increment, rather than as a single discharge. Effective discharge can be estimated using data on suspended sediment load, bed load, bed material, or total sediment load, with the method of estimation depending on the sediment transport characteristics of the stream, available data, and, to some degree, the researcher's school of thought. For this study, estimates of effective discharges are based on the suspended sediment load, which is the dominant load in most Illinois streams. Suspended sediment data collected at 88 gaging stations within Illinois were analyzed to determine which gaging stations in Illinois currently have sufficient suspended sediment data available to estimate effective discharges. A procedure was adapted from previous research and implemented to compute effective discharge values for each stream location having sufficient suspended sediment data. For each of those gaging stations, an estimate was made of the flow frequency at which the effective discharge was equaled or exceeded. For stations having adequate sediment data, flood recurrence intervals associated with effective discharge values were computed using annual maximum flow data. Correlation coefficients (r2) for 12 linear regressions are presented to describe the relationship between six effective discharge parameters and channel slope and watershed area. The data from 20 of the 88 gaging stations were deemed sufficient for computing effective discharge values. These 20 gaging stations were located on streams with watershed areas ranging from 244 to 6363 square miles (mi2). The relatively large watershed areas allow use of mean daily discharge values in computing effective discharge values. The annual maximum series analysis indicated that recurrence intervals associated with effective discharges found at these stations ranged from less than 1.01 years to 1.23 years. Such recurrence intervals are on the low end of the 1- to 3-year recurrence intervals commonly reported in other studies. However, these recurrence intervals are representative of Illinois' larger watersheds, and recurrence intervals of effective discharges in smaller Illinois watersheds could be quite different. Of the 20 qualified stations, 20 percent had effective discharge estimates that were less than the station's average mean daily discharge. Such low magnitude flow events are not usually associated with a stream's dominant discharge. Thus, geomorphic assessments and bankfull computations are required to further assess whether these and other effective discharge values are representative of the 20 individual streams' dominant discharges. Due to the small sample size, regression analyses relating specific effective discharge parameters to channel slope and watershed area were inconclusive. Effective discharge computations are particularly sensitive to how the sediment rating curve used in the computation is developed and the number of discharge classes used in the computation. The sampling frequency and duration over which the sediment samples used to create sediment rating curves also may influence effective discharge computations significantly. Thus, while stream restoration personnel will likely continue to use these and other effective discharge values as part of several tools in hydraulic and channel design applications, uncertainties in their use should be acknowledged and undue weight should not be assigned these values, as they cannot yet be expected to yield fully reliable results in applications. Like previous researchers, we recommend more comprehensive investigations that compare effective discharge estimates to bankfull discharges in combination with a geomorphic assessment of each stream's characteristics to yield a better understanding of whether currently computed effective discharge values adequately represent dominant discharges in Illinois. Suspended sediment represents the dominant sediment load in most Illinois streams. In some cases, effective discharge computations based on total loads or bed material loads may be more appropriate than using suspended sediment loads analyzed here. However, the bed load, bed material, bank material, local channel slope, and channel cross-section information required to perform these computations and analyses are almost nonexistent. While many of these data can be collected at selected stream locations, inherent difficulties in estimating bed loads in Illinois streams make this approach unfeasible. New technologies for sampling or estimating bed load most likely would need to be developed and tested. This analysis presents a comprehensive assessment of effective discharges based on the available suspended sediment and flow data in Illinois. Long-term sediment data sets are needed at more stream locations to more fully estimate and understand effective and dominant discharges in Illinois streams. The greatest need for additional data is for smaller watersheds less than approximately 200 mi2 because most potential applications of the effective discharge concept in stable channel design are for smaller watersheds. Smaller watersheds also may have significantly different geomorphic characteristics and effective discharges may behave differently than those in larger watersheds. The Illinois State Water Survey currently is measuring suspended sediment at gaging stations on 13 small watersheds, which could prove very useful in effective discharge analysis as longer data records become available at these sites.
Most if not all of the so called artesian aquifers in Illinois are actually leaky artesian aquifers. If the permeability of the confining bed is very low, vertical leakage may be difficult to measure within the average period (8 to 24 hours) of pumping tests. However, since the cone of depression created by pumping a well tapping a leaky artesian aquifer continues to expand until discharge is balanced by the amount of induced leakage, it does not follow that vertical leakage is of small importance over extended periods of time. As the cone of depression grows in extent and depth, the area of leakage and the vertical hydraulic gradient become large. Accordingly then, with long periods of pumping, contribution by leakage through a confining bed may be appreciable even though the vertical permeability is very low. If a source is available to replenish continuously the confining bed, the cone of depression developed by a well pumping for long extended periods will be influenced by the vertical permeability of the confining bed in addition to the hydraulic properties and geohydrologic boundaries of the main aquifer. Any long-range forecast of well or aquifer yield must include the important effects of leakage through the confining bed. The vertical permeability of a confining bed often can be determined from the results of pumping tests as described in this publication.
One of the main concerns was the ability to specify proper stage hydrographs at the downstream boundary of the Lower Illinois River for hydraulic design and analysis. We found that a unique stage-discharge rating relationship does not exist at the lower boundary of the Lower Illinois River at Grafton because of backwater effects from the Upper Mississippi River. Management options and results for managed storage and emergency activities need to be analyzed under more comprehensive design of flooding conditions. To improve the capability of UNET for modeling backwater effects for the Lower Illinois River, an extended model including Pool 26 of the Upper Mississippi River was developed. The downstream stations of the model are at the tail of Lock and Dam 25 and the Mel Price Lock and Dam pool, where stage readings are available. The model was calibrated with a 1979 flood and verified with a 1983 flood. Discharge and stage frequency analysis have also been performed for stations at Troy on Cuivre River, Lock and Dam 25 tail, Lock and Dam 26 pool, and Mel Price Lock and Dam on the Mississippi River.
This report is a cooperative project of the Illinois State Water Survey and StateGeological Survey. Part 1, prepared by the Geological Survey, discusses the geologic history and character of bottom sediments. Parts 2 and 3 were prepared by the Water Survey. Part 2 presents the hydraulic and hydrologic conditions of the Chain. Part 3 discusses the water quality and sources of nutrients and the living organisms. Part 3 also evaluates remedial measures found effective in other locations and proposes a reliable water managementprogram.