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 ground-water 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 ground water 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 ground-water levels in the Imperial Valley area. The purpose of the rain gauge network and the ground-water observation well network is to collect long-term data to determine the rate of ground-water 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 and November 1999, respectively. Precipitation is recorded for each storm that traverses the Imperial Valley, and ground-water levels at the 13 observation wells are measured the first of each month. The database from these networks consists of seven years of precipitation data and five years of ground-water observations. At the beginning of the ground-water observations in late 1994, the water levels were at their highest in the five years of observation. These high ground-water 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 below the 30-year normal. The 1997-1998 observation year had rainfall above the 30-year normal. Ground-water levels in the observation wells mirrored these rainfall patterns, showing a general downward trend during the dry years and a recovery in the wet 1997-1998 year. Seasonal increases in the ground-water levels were observed at most wells during the late spring and early summer, followed by decreases in August-November ground-water levels. Analysis indicates that the ground-water levels are affected by both the precipitation in the Imperial Valley area and the Illinois River stages. The observation wells closest to the Illinois River show an increase in water levels whenever the river stage is high. Generally, the water levels in the wells correlate best with precipitation and Illinois River stages one to two months before the water levels are measured, i.e., the June ground-water levels are most highly correlated with the Illinois River stage or precipitation that occurs in either April or May. The analyses conducted indicate the need for continued operation of both networks due to inconsistencies associated with ground-water levels, precipitation, and the Illinois River stage. For instance, the Mason-Tazwell observation well number 2 (MTOW-2) is located near the center of Mason County well away from the Illinois River, but it has an equal correlation with the Illinois River stage and the precipitation in the area. Additional analysis needs to be undertaken to explain this unusual finding.
The Illinois Streamflow Assessment Model (ILSAM) is an analytical and information tool developed to predict the frequency of streamflows, and water use impacts on streamflows, for every stream in selected major watersheds in Illinois. The current version of ILSAM was developed to operate on a personal computer having a Microsoft Windows 95/98/2000/NT operating system. The model user can obtain streamflow frequency estimates for any location in the watershed by identifying the desired stream and location. The ILSAM has been developed for use with streams in five such watersheds: the Sangamon, Fox, Kaskaskia, Kankakee, and Little Wabash River. This report includes a description of the steps used to develop ILSAM for application to the Little Wabash River watershed, along with a description of the physical characteristics of the watershed, its surface water hydrology, and the factors that influence streamflow variability. The Little Wabash River watershed is located in the southeastern portion of Illinois and has a total area of approximately 3238 square miles. The river and its major tributaries provide the source of water supply for all of the major communities in the watershed, either through direct withdrawals from the river or from the storage of water in impounding reservoirs. Many of these communities were forced to undertake emergency measures to sustain their water supply from these sources during the major droughts of the early- and mid-1900s. Thus, an understanding of the frequency of low flows and drought flows is critical for assessing surface water availability and yields for these communities. Streamflow frequency predictions produced by the model are also useful for evaluating instream flow levels for the protection of aquatic habitat, providing streamflow estimates for water quality analyses and regulations, and classifying Illinois streams by their hydrologic character for use in watershed management. The hydrologic analyses used to develop the model include evaluating the flow frequency from all streamgage records in the Little Wabash River region, evaluating impacts to flow quantity from dams, water supply, and treated wastewaters, and developing regional equations to estimate flows at ungaged sites throughout the watershed. All streamflow frequency estimates produced by the model are representative of the long-term expected flow conditions of streams, reflecting hydrologic conditions over a base period of nearly 50 years (1952-1999).
This is the third and final report on the Kankakee River in Illinois supported by the Conservation 2000 Program of the Illinois Department of Natural Resources. For this project, the Illinois State Water Survey mapped the bank erosion of the main stem of the Kankakee River from the Route 30 bridge in Indiana to the mouth of the Kankakee River with the Illinois River near Wilmington, collected about 100 bed and bank material samples, resurveyed all the previously surveyed river cross sections, surveyed four sand bars, and analyzed all historical and new data. This research has shown that of 223.6 river bank miles (includes both sides of the river), about 10.4 river bank miles have severe erosion, 39.4 river bank miles have moderate erosion, 70.8 river bank miles have minor erosion, and the remainder are either protected or stabilized or data are not available. The median diameter of the bed materials varied from 0.27 millimeters (mm) to 0.52 mm. The median diameter of bank materials varied from 0.07 mm to 0.41 mm. Analyses of the long-term flows from six gaging stations in Illinois showed an increasing trend in flows through the 1960s with no discernible increase since that time. Cross-sectional analyses of the river from the Kankakee Dam to the State Line Bridge did show some trends. The river reach from the Kankakee Dam to Aroma Park called Six-Mile Pool has lost 13.4 percent of its capacity due to sediment deposition since 1980. Similarly, Momence Wetland also has lost about 10.2 percent of its capacity since 1980. The section of the river between Aroma Park and Singleton Ditch showed both scour and sediment deposition. In general areas close to Aroma Park exhibited sediment deposition and the middle reach experienced scour. The recurring sand bar at the State Line Bridge area contains about 8,500 cubic yards of additional sediment in 1999 than were measured in 1980. The volumetric measurement of three additional sand bars showed some changes since 1980. The river is accumulating sediments within Six-Mile Pool and Momence Wetland. The middle reach is in semi-equilibrium with some sediment accumulation at several areas. Several management alternatives, both in-channel and watershed-based also are included to assist in the reduction of sedimentation problems of the Kankakee River.
Temporal fluctuations in the annual and summer precipitation across the Midwest during the 1898-2002 period are defined and described. Precipitation amounts were assessed for 15-year periods to show how patterns of precipitation have shifted spatially over the 20th Century. The early part of the century featured near average precipitation conditions, followed by predomi-nately dry conditions from 1928 through 1957. For example, during 1928-1942, 96 percent of the Midwest had below average precipitation. After 15 years with near average conditions from 1958 to 1972, extremely wet conditions developed during 1973-2002, with 91 percent of the Midwest experiencing above average precipitation. Extreme precipitation values sampled during each 15-year period revealed temporal differences with much more extreme amounts during wet and dry periods than during near average periods. Annual totals reflected the long-term variations in summer rainfall, revealing the importance of summer rainfall in determining annual amounts. Regionally, amounts were below average more frequently in the southern Midwest than in the central and northern Midwest. Values were above average more frequently in the northern Mid-west than in the central and southern Midwest. The results provide information that should be useful for hydrologic and agricultural planning and assessments.
GENTLEMEN : Herewith I submit a report on the ground water resources of the State of Illinois and recommend that it be published as Bulletin No. 21. Since the Directors' report includes a statement of the general activities of all divisions, it has seemed advisable to discontinue the publication of an annual report of this division and to prepare instead summaries of our various investigations as they are completed. This policy was adopted with the publication of Bulletin No. 18 in May of 1922, and has been followed since that date. A portion of this material has appeared in abstract form in annual reports published prior to 1920. That material was too meager and scattered to be of practical value. In the present collected form we believe this data will be of very considerable value to the State of Illinois. Respectfully submitted, A. M. BUSWELL, Chief.
Sedimentation detracts from the use of any water supply lake by reducing lake depth and volume, with a reduction of reserve water supply capacity and possible burying of intake structures. Sedimentation of a reservoir is a natural process that can be accelerated or slowed by human activities in the watershed. Lake Decatur is located in Macon County, northeast of Decatur, Illinois. The location of the dam is 39 49 28" north latitude and 88 57 30" west longitude in Section 22, T.16N., R.2W., Macon County, Illinois. The dam impounds the Sangamon River in the Sangamon River basin. The watershed is a portion of Hydrologic Unit 07130006 as defined by the U.S. Geological Survey. The lake was constructed in 1922 with a spillway level of 610 feet above mean sea level (feet-msl). In 1956, a set of hydraulic gates was installed on the original spillway to allow variable lake levels from 610 feet-msl to 615 feet-msl. The portion of the lake surveyed for the present study was Basin 6 located above Rea's Bridge Road. This basin of the lake is the headwater area of the main body of the lake. Lake Decatur has been surveyed to document sedimentation conditions eight times since 1930. Five of these survey efforts (1936, 1946, 1956, 1966, and 1983) were sufficiently detailed to be termed full lake sedimentation surveys. The present survey is not considered to be a full lake sedimentation survey. Sedimentation has reduced the basin capacity from 2,797 acre-feet (ac-ft) in 1922 to 1,451 ac-ft in 2000. The 2000 basin capacity was 48.1 percent of the 1922 potential basin capacity. For water supply purposes, these volumes convert to capacities of 911 million gallons in 1922 and 473 million gallons in 2000. Sedimentation rate analyses indicate a decline in annual sediment deposition rates from 35.4 ac-ft for the period 1922-1936 to 8.3 ac-ft annually from 1983-2000. The long-term average annual deposition rate for 1922-2000 was 17.3 ac-ft. Density analyses of the sediment samples indicate that the unit weight of sediment in the northern (upstream) portions of the lake is greater than the unit weight of sediment in the southern end of the lake. In general, coarser sediments are expected to be deposited in the upstream portion of a lake where the entrainment velocity of the stream is reduced to the much slower velocities of a lake environment. These coarser sediments tend to be denser when settled and are subject to drying and higher compaction rates as a result of more frequent drawdown exposure in the shallow water environment. As the remaining sediment load of the stream is transported through the lake, increasingly finer particle sizes and decreasing unit weight are observed.
Lake Decatur is the water supply reservoir for the City of Decatur. The reservoir was created in 1922 by constructing a dam to impound the flow of the Sangamon River with an original water volume of 20,000 acre-feet and an area of 4.4 square miles. The dam was later modified in 1956 to increase the maximum capacity of the lake to 28,000 acre-feet. Water withdrawal from the lake has been increasing over the years, averaging 37 million gallons per day (mgd) in 1994. The drainage area of the Sangamon River upstream of Decatur is 925 square miles. The watershed includes portions of seven counties in east-central Illinois. The predominant land use in the watershed is row crop agriculture comprising nearly 90 percent of the land area. The major urban areas within the watershed are Decatur, Monticello, and Gibson City. Lake Decatur has high concentrations of total dissolved solids and nitrates, and nitrate concentrations have been exceeding drinking water standards in recent years. This has created a serious situation for the drinking water supply of the City of Decatur. The Illinois Environmental Protection Agency (IEPA) has issued nine nitrate warnings to the city from 1979 to 1996 for noncompliance with Nitrate-N concentrations in Lake Decatur have exceeded the Illinois Environmental Protection Agency (IEPA) drinking water standards for nitrate when concentrations exceeded of 10 milligrams per liter (mg/l) for the period between 1979 and 1998, except from 1993 to 1995. On June 10, 1992, a Letter of Commitment (LOC) was signed between the IEPA and the City of Decatur. The LOC requires the city to take several steps to reduce nitrate levels in Lake Decatur to acceptable concentrations within nine years of signing the LOC. Nitrate-N cannot be removed from finished drinking water through regular water purification processes. One of the steps required the city to conduct an initial two-year monitoring study of the Lake Decatur watershed to better understand nitrate yields in the watershed. In 1993, the Illinois State Water Survey received a grant from the City of Decatur, conducted a two-year monitoring study, and developed land use management strategies that could assist the city comply with the IEPA drinking water standards (Demissie et al., 1996). This technical report presents the annual data for all six years of monitoring (May 1993-April 1999) and monthly data for the sixth year of monitoring (May 1998-April 1999).
This investigation is the first of three phases of a ground-water management study. In this report, effects of irrigation and drought on the ground-water resources of Illinois are examined. Irrigation water use for five soil types is estimated from a monthly water budget model on the basis of precipitation and temperature data from the last 30 years at selected weather stations across Illinois. Moisture deficits are computed for each soil type on the basis of the water requirements of a corn crop. It is assumed that irrigation is used to make up the moisture deficit in those places where irrigation systems already exist. Irrigation water use from each township with irrigated acreage is added to municipal and industrial ground-water use data and then compared to aquifer potential yields. The spatial analysis is accomplished with a statewide geographic information system. An important distinction is made between the seasonal effects of irrigation water use and the annual or long-term effects. The model is tested for its sensitivity to weather variation; seasonal water deficits are calculated by using data from extreme growing seasons and extended drought periods. The effect of increasing the amount of irrigated land by 50 percent is also considered for normal weather conditions and droughts. The effect of variable irrigation demand on ground-water resources is expressed as the ratio of ground-water use to ground-water potential yield for each township. This is done to highlight regions most susceptible to ground-water stress because of drought or increased irrigation by showing where use could exceed yield. The sensitivity of the results is not tested for variations in spatial aggregation. This will be one of the primary tasks in subsequent study phases. Results show that irrigation is a substantial seasonal consumptive ground-water use in Illinois, with the potential for growth. However, present effects appear to be localized and highly dependent on weather conditions. Some potential for seasonal or temporary overpumpage may exist in the heavily irrigated areas during years with below-normal precipitation or during extended droughts. The aquifers being used for irrigation appear to have the ability to recover from present irrigation demands without suffering significant depletion, implying that the annual effect of irrigation is currently relatively minimal. The exception to this may be during extended drought periods, especially if widespread expansion of irrigation practices also occurs in the state. A 50 percent expansion of irrigation would appear to have surprisingly little additional impact on ground-water resources under most climatic conditions. That degree of growth around currently irrigated land would result in expanded irrigation areas still within reach of the productive, high-yielding aquifers already being pumped for irrigation. A much larger degree of irrigation expansion into areas with heavier-textured soils is possible in Illinois. The availability of ground-water would be a major limiting factor in the speed and direction of that expansion. That kind of massive irrigation expansion is not considered in this report; however, its effects on the state's ground water are assumed to be considerable and will be addressed in subsequent study phases. The Chicago metropolitan area stands out as a major region of overpumpage, but not because of irrigation. Variable irrigation pumpage does appear to consistently affect several other regions, most notably parts of Mason, Kankakee, Tazewell, Lee and Whiteside Counties. The degree to which these counties are affected by irrigation depends largely on weather conditions. For all these counties, with the possible exception of Kankakee, surficial sand and gravel aquifers are the most susceptible to stress from drought and irrigation water use. Shallow bedrock aquifers may also be impacted by irrigation in parts of Kankakee County. The impact of an extended drought is likely to be more widespread and inconsistent because of the multiple effects of increased water use for irrigation and other demands, and reduced ground-water storage.
Riparian forests have been proposed by the Technical Advisory Subcommittee of the Upper Embarras River Basin Commission in its alternatives for mitigating flood damages in the Village of Villa Grove and nearby farmlands. In order to evaluate potential reduction in flood stages in Villa Grove, methods for accounting for flow resistances induced by the riparian forests are needed in the hydraulic model for the Upper Embarras River. This project has been designed to better apply the available knowledge in practical field applications, particularly, how to evaluate the vegetal roughness in terms of Manning's andlt;EMandgt;nandlt;/EMandgt; coefficient for specified planting scenarios. Approaches presented in this report are literature review on Manning's roughness with emphasis on vegetative roughness, and evaluation and selection of methods for computing vegetative roughness due to riparian forests. The Petryk and Bosmajian (1975) method was selected for evaluating Manning's andlt;EMandgt;nandlt;/EMandgt; for mature trees because parameters could be reasonably obtained with available general field information. Using this approach, effects of riparian forest on floods were evaluated with the scenarios that the two-year floodplain has two densities of trees. The study reach was the channel between Villa Grove and Camargo. Also investigated were the options of having uniform tree density for the whole reach or half of the reach. An interface has been developed for implementing the computed andlt;EMandgt;nandlt;/EMandgt; values to a HEC-RAS hydraulic model, and capacity curves were developed to illustrate the effects on flood conveyance among these scenarios. The capacity curves thoroughly included possible boundary conditions and were presented in simple nomographs that relate discharge and downstream elevations to a specified flood elevation in Villa Grove. Therefore it was easier to evaluate the resulting effects of different alternatives.
The Illinois Streamflow Assessment Model (ILSAM) was developed to provideneeded streamflow information to watershed managers and planners. This specialized software program was developed for use on a personal computer to provide estimates of the long-term expected magnitude of streamflow at various frequencies for any stream location along a major stream in a watershed.The purpose of this study was to update ILSAM for the Fox River Basin, a modeloriginally developed in 1988. Over time, climate variability and changes in humanfactors, such as land and water use, and water resource projects, can greatly affect the quantity and distribution (both in space and time) of surface waters in a river basin. For this reason, the data sets used by ILSAM were designed to be updated periodically, perhaps every 5 to 15 years. The frequency of and need for updates are governed by the rate at which streamflow conditions in the watershed change over time. The model update for the Fox River Basin addresses four areas that influence the flow frequencies and their estimation:- Increases in population, overall water use, and the resulting effluent discharges.- A new public water supply withdrawal from the Fox River and increases inmagnitude of existing withdrawals.- General increases in streamflow magnitude caused by climatic variability and the overall increase in average precipitation.- Adoption of improved regional equations from which to estimate flow at ungaged s i t e s .