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 .
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.
The State Water Survey of Illinois began the investigation of the waters of the State in 1895. While the Survey has laid special stress on the determination of the character of the waters from a sanitary standpoint, it has also often been called upon to make analyses of the mineral content to determine its character from a medicinal or commercial standpoint. In the various reports so far issued by the Survey only results of the sanitary investigations were published. It had been the intention to publish the results of the mineral analyses in a previous report but this had to be postponed until the present time when, in cooperation with the Geological Survey, it has become possible. This Bulletin, primarily, contains the records of the analyses made to determine the composition of the mineral residue with reference to the value of the water for manufacturing and medicinal uses, but there are also included the sanitary analyses, wherever such analyses have been made.
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).
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.
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.
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 and municipal, industrial, 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. 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 rain gauge network and the groundwater observation well network collect long-term data to determine the rate of groundwater level decline in dry periods and during the growing season, and the rate of groundwater level recovery during recharge periods. This report presents data accumulated from the rain gauge and observation well networks since their inception through August 2001. 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 nine years of precipitation data and seven years of groundwater observations. At the beginning of groundwater observations in late 1994, the water levels were at their highest in the seven 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 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 dry years, a recovery in wet 1997-1998, and a leveling off in near-normal 1998-1999, followed by declines in dry 1999-2000. Despite a dry July, near-normal precipitation in 2001 brought a return to more typical seasonal hydrographs. This report includes new regression analyses of data collected through August 2001, similar to regression analyses first conducted on data collected through August 1998. The analyses indicate that groundwater levels are affected by 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; e.g., a high correlation between June groundwater levels and the Illinois River stage or precipitation that occurs in April or May. However, additional data collected since 1998 did not improve the results of the regression analyses. In fact, coefficients of determination for many regressions worsened. This suggests that regressions of observed groundwater levels versus river stage and precipitation are not adequately describing all the variables affecting groundwater levels. Using the data collected to verify, test, and improve the existing Imperial Valley groundwater flow model is highly recommended. Continued data collection also is recommended to create long-term data sets of precipitation and groundwater levels for use in modeling analyses. Collection of additional groundwater level and irrigation pumpage data also is highly recommended.
The Vermilion River and Little Vermilion River watersheds lie in seven counties in east-central Illinois and west-central Indiana. The drainage areas of the Vermilion River and Little Vermilion River at their confluences with the Wabash River are 1434 and 244 square miles, respectively. The Vermilion River meets the Wabash River at river mile 257.4 and has three tributaries: North Fork, Middle Fork, and Salt Fork. The Little Vermilion River is a direct tributary of the Wabash River at river mile 247.8. Lake Vermilion, a 660-acre impounded reservoir located on the North Fork Vermilion River, is the main municipal drinking water supply for the City of Danville, Illinois. The Little Vermilion River is the main tributary for the 63-acre Georgetown Reservoir, the municipal drinking water supply for the community of Georgetown, Illinois. Approximately 88 percent of the watersheds for both rivers are in agricultural production with approximately 5 percent in forest/woodlands and wetlands. The Illinois State Water Survey (ISWS) conducted a two-year watershed monitoring study of the Vermilion River and Little Vermilion River watersheds for the Vermilion River Ecosystem Partnership-Conservation 2000 Ecosystem Program. The purpose was to assist the partnership by establishing a baseline of hydrologic and water quality data to provide a better understanding of the cumulative impacts of future best management practices implemented in the watersheds. The ISWS established a streamgaging station on the Little Vermilion River near Sidell and monitored the hydrology, sediment, and nitrate-nitrogen (nitrate-N) there and at three U.S. Geological Survey (USGS) streamgaging sites in the Vermilion River watershed (Middle Fork Vermilion River above Oakwood, North Fork Vermilion River near Bismarck, and Vermilion River near Danville). Annual sediment loads for the three Vermilion River watershed stations were approximately three times higher than loads at the Little Vermilion station. The Middle Fork station had the highest sediment loads among the three Vermilion River stations for both project years. The North Fork station had the highest annual nitrate-N load for both monitoring years. In general, annual sediment and nitrate-N loads were lower during the first monitoring year, due to below average spring season runoff. Sampling for three pesticides (atrazine, alachlor, and metolachlor) was done on a weekly basis from June to October 2002. Atrazine was the only pesticide detected during this period. The highest level sampled was 20.93 micrograms per liter (and#956;g/L) and, and all others were below 2.65 and#956;g/L.
Soil erosion and nonpoint source pollution runoff rates are estimated using output from the Revised Universal Soil Loss Equation (RUSLE). The underlying influence of climate on surface transport processes as represented in the RUSLE is carried within one constant, the R-factor. It has been assumed that the R-factor is temporally stationary; that is, it does not change with time. The purpose of this study was to process climate information from the most recent decades to update the R-factor, to examine the nature of precipitation variation and change and their impacts on the R-factor over space and time, and, specifically, to test the hypothesis that storm erosivity and the R-factor are temporally stationary. This was addressed by developing a database of precipitation data and related information needed to calculate single-storm erosivity and cumulative R-factor for each half-month of the year and for the total year. In addition the 10-year, single-storm erosive index for each station is provided. The R-factor, a nonlinear, cumulative measure of the erosive energy contained in storm precipitation, was calculated directly from 15-minute rainfall data. However, because of some undocumented quality difficulties with the 15-minute data, single-storm erosivity index statistics for accumulation into R-factors were calculated from more reliable daily data through the use of a power law transfer function. These new R-factors were tested for spatial covariation, which was found to be minimal in even terrain, and related to the limited amount of station R-factor data from past studies. Comparison with past R-factor studies indicated strongly that the methodologies used adequately duplicated old R-factors based on data from the 1930s to the 1950s. General increases observed in R-factors in this study were related to increasing amounts of precipitation and storms with rainfall greater than 12.7 millimeters, especially in the western United States. Mean seasonal patterns of storm precipitation total, duration, intensity, 30-minute and 15-minute maximum intensity, kinetic energy, erosivity, and the numbers of storms also were mapped for the conterminous United States. These analyses showed distinct patterns of precipitation change with seasons and identified regions of strong gradients where climate change first may be noticed. Trend analyses of storm precipitation variables over the 1971-1999 period indicated the lack of temporal stationarity of storm characteristics. Storm duration changes were especially an important cause of the observed changes in storm precipitation totals. However, storm trends in 30-minute maximum intensity seemed to be more important in changing the patterns of storm erosivity. Examination of storm characteristic response to interannual and interdecadal variations also indicated that storm characteristics were responding at these time scales to large-scale climate system forcings. In the winter season, atmospheric teleconnections such as the Pacific/North American Pattern and the North Atlantic Oscillation were shown to influence not only storm track positions and the number of storms at a location, but also the characteristics of individual storms. El Nio and La Nia events of the Southern Oscillation (ENSO events) had distinctive impacts on storm variables in every season of the year. Even the Pacific Decadal Oscillation showed a clear effect on storm characteristics, especially in the western United States. The results of R-factors derived from modern data compared to previous R-factors combined with storm characteristic trend and variability studies indicate conclusively that storm precipitation characteristics change sufficiently over time to warrant an evaluation of the necessity to recalculate R-factors on a regular basis.
The Cache River located in the southernmost part of Illinois flows through an area containing the Cache River Wetlands. These unique and important wetlands were designated as a Ramsar Site in 1996. Drainage activities divided the Cache River in half in the early 1900s, effectively separating the river into the Upper and Lower Cache Rivers. The Lower Cache River contains a remnant of a vast wetland system called the Lower Cache River State Natural Area (LCRSNA), commonly referred to as Buttonland Swamp. Sediment inflow from several tributary streams has an impact on the wetland. Previous research has determined that 217,000 tons of sediment were deposited in Buttonland Swamp between 1986 and 1988. The wetlands of the Lower Cache River have been targeted for preservation and restoration by state, federal, and private environmental organizations. A program to monitor the sediment deposition rate within the wetland area at regular intervals would be useful in evaluating and guiding preservation and restoration efforts. This project established a benchmark measure of the deposition rates and cross-sectional profiles at selected locations in the LCRSNA wetland.