From The Changing Illinois Environment: Critical Trends, Volume 2: Water Resources , Technical Report of the Critical Trends Assessment Project
Illinois is considered a water rich state. In one sense the state is surrounded by fresh water--major river systems border its west, south, and east boundaries; and Lake Michigan borders the northeast. The interior is crossed by several large tributaries of these major border rivers. These rivers and Lake Michigan are the major surface water resources of the state. In addition, the state has abundant groundwater resources; however, the distribution of these is not uniform throughout the state, making their availability variable. Many climatological and socioeconomic factors influence the quantities and qualities of the water resources in Illinois. This section details the impacts on Illinois water resources by one relatively infrequent but consequential condition: drought.
Studying drought conditions heightens our awareness of the impacts of drought and serves as a basis for planning for future drought conditions. It is essential that drought conditions be investigated because droughts are defined by a mixture of a) their physical dimensions (such as percent of normal rainfall or streamflow), and b) their socioeconomic impacts (Changnon, 1980). A drought cannot be truly defined until some form of human endeavor or the environment begins to experience stress from a water deficiency. Ever changing land uses and water management facilities, such as new water supply lakes, stream channelization, and new ways of planting crops, collectively affect water quantity and quality. These in turn are affected differently by deficiencies of moisture, thus making historical analysis of drought conditions necessary (Changnon et al., 1982).
There is no one definition of a drought. A summer dry period lasting several weeks may constitute an "agricultural drought," but hardly qualifies as a drought with respect to its impacts on streamflow, reservoirs, or ground water. One or more years of deficient precipitation may be needed before certain water demand areas are affected and thus denote a drought (Changnon, 1980). Regardless, the identification of a drought generally requires some socioeconomic impact resulting from a lack of water. Changnon et al. (1982) identify five categories of possible drought impacts:
Public water supplies Agriculture and rural dwellers Transportation Recreation and the environment Social behavior and health
The following discussion of drought impacts focuses primarily on the first of the five impacts, i.e., public water supplies, and the physical characteristics (stream flow and groundwater levels) that directly impact water supplies. Drought impacts on barge transportation are also briefly covered. Other impacts are not ad-dressed largely because of available time, and in some cases little available data. The interested reader can obtain details of individual droughts from several past Water Survey reports, which are summarized below.
The Illinois State Water Survey (ISWS) is mandated to collect and disseminate water resource information in Illinois. As part of this mandate, several documents have been published detailing various aspects of droughts. Reports such as ISWS Bulletin 50, Drought Climatology of Illinois (Huff and Changnon, 1963) and Droughts in Illinois: Their Physical and Social Dimensions (Changnon et al., 1987), provide general descriptions of drought related phenomena in Illinois. Additional studies by Gerber (1932), Hudson and Roberts (1955), Changnon et al. (1982), Lamb et al. (1992), and Riebsame et al. (1991) focus on the characteristics and impacts of specific drought periods.
Changnon et al. (1982) summarized the drought period of 1980-1981, detailing the climatological, meteorological, streamflow, and groundwater conditions and impacts during this time. Four major recommendations were presented to allow for better planning for future drought conditions:
1. Develop more informed and organized local and state programs for addressing droughts in Illinois. Education in water conservation and management would allow a more informed, less frantic response to drought conditions. 2. Renovate older water supply systems. These are the systems that tend to come under stress very easily and quickly in times of drought. 3. Employ water conservation, water reuse, and higher water prices based on true value and limits of this resource. 4. Develop and use new and emerging technologies to assist in increasing water supplies and to apply these technologies concurrently with improved water management practices.
With the development of stricter Illinois Environmental Protection Agency regulations in regard to public water supply systems, the development and strengthening of large professional organizations (such as the American Water Works Association) in Illinois, and better resource tracking programs by state environmental agencies, steps have been taken toward implementing many of these recommendations.
Lamb et al. (1992) described the meteorological causes and climatological characteristics of the drought of 1988-1989, and assessed the diverse impacts of the drought on soil moisture, plant water use, surface heat exchanges, streamflows and lake levels, groundwater conditions, and agricultural production. This report also includes a description of the administrative framework used by the state of Illinois to address drought-induced water problems. This infrastructure had largely evolved and was partially shaped by the recommendations of the 1982 report. Drought management strategies recommended in the 1982 report were also used on a real time basis during the 1988-1989 drought to monitor and respond to the drought related problems that emerged.
Impacts on Surface Water Resources
Physiographic and Geographic Influences in Surface Water Droughts
Streamflow during a drought period originates almost entirely from subsurface storage that seeps into the streambed. From a simplistic concept, this baseflow can be viewed as originating from two sources: 1) the soil and subsoil, and 2) shallow ground water. The soil/subsoil contribution is greatly impacted by periods of extreme below-normal rainfall during summer and fall (typically lasting four to six months) when soil moisture supplies are already depleted by high evapotranspiration rates. Shallow ground water is depleted over a longer period of time, and typically is at its lowest only when there is below-normal rainfall (and hence low groundwater recharge) during the previous spring. A combination of these two factors, i.e., a dry spring followed by an extremely hot and dry summer, will produce the most severe low flows. The extent to which a particular stream is impacted depends partly on physiographic differences across the state.
Southern Illinois. In most southern Illinois watersheds, relatively small amounts of shallow ground water are contributed to streams. For this reason, streams will experience low flows following any hot, dry summer. The flow may be especially low if preceded by a dry spring.
Central Illinois.The shallow groundwater contribution to streamflow in central and western Illinois is considerably greater than in the south, yet less than the northern portion of the state. For significant drought flow conditions to occur, it is generally necessary to have both a dry spring and a hot, dry summer.
Northern Illinois. Baseflow in northwestern Illinois streams occurs at high rates, and the predominant portion of this baseflow originates from both shallow ground water and from bedrock aquifers that are intersected by the stream. In many cases, low streamflows are relatively independent of summer conditions and occur only when preceded by one or two years of low recharge. Baseflow in northeastern Illinois streams is closer in character to that of central Illinois streams.
Sandy Regions. A relatively small portion of Illinois has sandy soils. The most notable are the Kankakee-Iroquois River basins and the Havana Lowlands in Mason County. Low streamflows in these areas are most greatly impacted by periods of both precipitation deficit and high evapotranspiration rates. The lowest streamflows therefore primarily occur at the end of hot, dry summers. Once cooler temperatures arrive in the fall, streamflow levels in these areas have a chance to rebound.
Data Sources - Measures of Drought Severity and Impacts
Three types of data are available to analyze surface water drought and its impact on public water supplies: 1) reservoir and lake levels, 2) streamflow, and 3) records on the number of communities impacted by deficient water supplies, the types of impacts, and adjustments made to address the drought.
The Water Survey has maintained monthly water level measurements on selected Illinois reservoirs since 1967. The total coverage has gradually increased from 10 reservoirs in 1967 to 38 reservoirs in early 1993. Most of these reservoirs are used for public water supply. Water levels for some reservoirs have been reported periodically in Water Survey memoranda dating back to the 1920s.
The second type of data, streamflow levels, have been recorded at more than 300 locations in Illinois since 1908. Continuous flow records cover periods lasting less than one year to more than 78 years. Approximately 240 gages have at least ten years of record. These gages have been maintained by the U.S. Geological Survey, with cooperation and funding from various state, federal, and local agencies.
The third type of data describe the number of communities impacted by deficient water supplies. Sources for these data include: 1) the ISWS reports on the impacts of individual droughts (Gerber, 1932; Hudson and Roberts, 1955; Changnon et al., 1982; and Lamb et al., 1992), 2) records on the construction of new water supply reservoirs and other water resource projects--actions that typically follow a drought during which supplies are found to be inadequate, and 3) weekly drought newsletters produced by the Illinois Environmental Protection Agency during the 1998 drought, which detail water supply conditions for communities seeking drought assistance.
Reservoir and Lake Levels
Reservoir levels can provide an excellent measure with which to compare the severity of different droughts. For example, table 1 presents the minimum reservoir levels recorded at Lake Decatur during seven different droughts. These measurements suggest that the 1954 drought was by far the most severe on record, followed by those of 1930 and 1940. But changes in water use, reservoir sedimentation, and the addition of other water supply sources can change the relative impact associated with measured water levels. For Decatur, the 1988 drought is believed to have had a more severe impact than the 1930 and 1940 droughts for three reasons: the water use of Decatur had increased threefold by 1988, sedimentation had reduced the storage in the reservoir, and the normal pool elevation of Lake Decatur had been raised in 1958 from 610 feet to 613.5 feet.
Lake Michigan Water Levels. The major sources of inflow to Lake Michigan are Lake Superior and tributaries located in Wisconsin and Michigan. Precipitation over the lakes is also a major source of water. Illinois contributes only a very small amount of the total inflow to the lake. Thus the lake is most directly impacted by widespread droughts that cover most of the north-central United States, as opposed to droughts that may only impact Illinois. On the other hand, most of the historical droughts that significantly impacted Lake Michigan water levels (1934, mid-1950s, 1963-1964, and 1988-1989) were also severe droughts in Illinois. Records on Lake Michigan levels have been kept since 1860. Figure 1 shows these levels over the period 1961- 1992. This period covers both the lowest and highest water levels measured on Lake Michigan in the 20th century--a low of 575.4 feet above mean sea level in 1964, and 582.6 feet in 1986. Low levels during both the 1926 and 1934 droughts were similarly low (575.6 feet). It is not clear how much the increased diversion from Lake Michigan in the early twentieth century affected these earlier droughts. The 1988-1989 drought was significant--lake levels dropped 4 feet between late 1986 and early 1989.
Though the 1986 Lake Michigan level was the highest recorded this century, higher values were recorded during several years between 1860 and 1886. The maximum lake level is 583.0 feet, recorded in 1886. Given these earlier records, it is not reasonable to suggest a long term increasing trend in lake levels--perhaps we have merely returned to a period of wet conditions similar to those that existed more than a century ago.
The minimum drought streamflow provides the most direct quantitative assessment of that drought's impact on direct withdrawals from streams. Cumulative streamflow over a critical drought period provides an indirect measure of a drought's impact on withdrawals from water supply reservoirs.
Table 2 ranks droughts for the period 1915-1991 based on streamflow records from six long term gaging stations. Three droughts--1930-1934, 1952-1955, and 1962-1964--are notable for their severity, duration, and widespread impact. For four out of the six stations, the 1952-1955 drought was the most severe on record. An examination of rainfall records by Knapp (1990) indicates that the 1893-1895 drought may have had as extensive an impact as the 1952-1955 drought in many parts of Illinois. However, there are no streamflow records for this earlier drought.
The major difference between a moderate and severe streamflow drought is usually related to the duration of the drought. Since 1965, three shorter droughts are generally considered to have been moderate in nature: 1976-1977, 1980-1981, and 1988-1989. For much of Illinois, the 1988-1989 drought was intense, but lasted less than nine months. But in western and west-central Illinois (the Spoon River at Seville and the LaMoine River at Ripley) this drought started in 1987 and ended late in 1989. For this region of the state, the drought of 1988-1989 was severe, and for several locations it is the drought of record.
Number of Communities Having Water Shortages
The impact of a drought on a surface water supply system depends greatly on the source of the supply as well as the intensity and duration of the drought. Systems that obtain water from a low channel dam or by direct withdrawal from a stream are susceptible to any short, intense drought that causes low flow (up to two months in duration). Reservoirs with a great deal of storage (relative to both the average inflow and water use) are designed to supply water for multiyear droughts, and therefore may not be severely impacted by short, intense droughts. Table 3 describes the drought duration that is most critical for selected reservoirs.
The impact on surface water supplies is usually preceded by a relatively long period of below-normal precipitation. There is no exact definition of when a drought starts, and the drought may be well developed by the time it is recognized. The initial stages of a drought typically have hot and dry weather, promoting increased water use, which then amplifies the impacts of the dry conditions. When the threat to the adequacy of a water supply system is finally recognized, water use restrictions and conservation measures may be employed to reduce the impact of the drought.
Table 4 lists the number of public water supplies that experienced shortages during selected droughts. Because this table includes estimates from different sources, there is likely some variation in the criteria used to identify a drought shortage. Hudson and Roberts (1955) suggest that a reservoir is suffering a shortage when less than six months of capacity remains in the reservoir by the end of a drought. This may be appropriate except for reservoirs with short critical durations (such as Decatur).
Another measure of the number of communities experiencing drought can be seen in the steps taken during and after the drought to mitigate or correct water supply deficiencies. Reactions to mitigate the impacts of drought include changes in water treatment, enforced conservation, and short-term additions to the existing storage supply (such as adding wells for emergency supply). More major actions, often following a drought, include raising dam spillways, installation of pipelines, and in extreme cases, developing new reservoirs (Changnon and Easterling, 1989).
The construction of new reservoirs for public water supply use has often followed a major drought, during which the inadequacy of the current system is made evident. The two major periods of reservoir construction in Illinois (see figure 5 in the section on Water Supply and Use) were the 1930s and the 1960s, each following major droughts. No new reservoirs for public water supply use have been constructed since 1978. However, other actions have been taken during this time to supplement existing sources or to develop new supplies. Table 5 provides examples of the steps that have been taken to improve surface water supplies since 1972.
Are these public water supplies better equipped to handle drought conditions than in the past? Certainly for specific systems the threat of drought is much less. The development of the Rend Lake Intercities Water System in 1972 provided an abundant supply of water to much of southern Illinois and replaced several existing reservoir systems, many of which were inadequate. Many other communities are now interconnected with larger systems or have developed supplemental supplies that provide a long range solution to possible water shortages.
But Broeren and Singh (1989) estimate that at present, 25 surface water systems would be inadequate during a 50-year drought without considerable water conservation. Another ten systems would likely have a small amount of supply at the end of the drought, so that they too would be considered to have shortages. Thus it is possible that 35 out of 90 existing systems, approximately 40 percent, would be severely impacted. While this is an improvement over the percentage of systems that had shortages during the 1930-1931 and 1952-1955 droughts, it is not a particularly significant one. The 1988-1989 drought was a moderate one for many areas of the state, yet 18 public water supplies were significantly impacted. What will happen when a longer severe drought occurs? It remains to be seen how helpful lessons learned from the 1988-1989 drought will be.
Impacts on Navigation
The impacts of low flows on barge traffic during the 1988 drought have been well documented by Chang-non (1989), whose work is briefly summarized here. In June 1988, insufficient water depth and the creation of shoals severely impeded the movement of barges on the Ohio and Mississippi Rivers. Barge traffic was halted twice in June and July 1988 on the Ohio River near Cairo as well as farther downstream on the Missis-sippi River so that dredging could clear a navigation channel. Loads were restricted to reduce the draft of the barges, and total river traffic was down by 20 percent (Changnon, 1989).
The conditions that led to the interruptions in barge traffic in 1988 are rare, yet it is estimated that similar or more severe low flows existed on the Mississippi River in the 1930s and 1950s, but the barge industry was not as well developed then as in 1988 (Koellner, 1988). In all three cases (1930s, 1950s, 1988) the low streamflows were preceded by at least 12 months of below normal rainfall and the drought conditions were widespread, covering the entire Upper Mississippi River basin.
Impacts on Groundwater Resources
The effects of a drought on ground water are governed by the variables of the groundwater budget. This budget is a part of the general hydrologic budget and assumes that over a long period of time, water gains by a drain-age basin will be balanced by water losses within that drainage basin. The groundwater budget for a given watershed can be stated in the form of a simple equation:
Pgw = Rgw + ETgw + U + Sgw in which the groundwater recharge within a given basin (Pgw) over time is balanced by groundwater runoff (Rgw), evapotranspiration (ETgw), underflow (U), and change in groundwater storage (Sgw).
Groundwater recharge (Pgw) occurs when infiltrated precipitation exceeds surface evapotranspiration and soil moisture requirements. Most recharge occurs during the spring when evapotranspiration is small and soil moisture is maintained at or above field capacity by frequent rains. Little recharge occurs during summer and early fall, when evapotranspiration and soil moisture requirements normally exceed precipitation. Recharge is also negligible during the winter months when the ground is frozen.
Most of the groundwater recharge will eventually discharge into one of the basin's streams (or other surface water bodies) as groundwater runoff (Rgw), or leaves the basin as underflow (U). Underflow is the net movement of groundwater from the area (or drainage basin) of interest to adjacent areas. The amount of groundwater runoff is a function of the hydraulic gradient (slope) of the water table, the position of the water table relative to the streambed level, and the hydraulic properties of the water-bearing formation.
Groundwater evapotranspiration (ETgw) is the process by which moisture is extracted from below the water table and brought to the near-surface, where it either evaporates or is used by plants in transpiration. Losses to evapotranspiration (ETgw) are greatest during the growing season, May through October, and are particularly great in mid to late summer. The potential for groundwater evapotranspiration increases as the water table approaches the land surface, where the roots of plants can capture the water and soil capillaries can draw ground water nearer to the surface, allowing warm air to evaporate the water.
Changes in groundwater storage (Sgw) are governed by the processes of recharge, groundwater runoff, underflow, and evapotranspiration. Recharge and evapotranspiration, in particular, have considerable seasonal variation and, as a result, so does the groundwater storage (and thus well levels). Annual changes in groundwater storage, and in particular the changes during drought events, are most closely related to changes in the amount of groundwater recharge. As explained below, this impact may be observed at various times.
Recharge to near surface deposits can occur at relatively high rates, especially when these deposits contain significant amounts of sand and gravel. However, large areas of Illinois are covered by fine grained glacial drift, which commonly exceeds 50 feet in thickness. Sand and gravel and bedrock aquifers are often deeply buried under this material, which typically has low vertical permeability. In these cases, recharge to many of the deep aquifers is limited to slow leakage through the drift. This recharge and ultimately, storage, are the components of the groundwater budget that are impacted during drought conditions.
The Water Survey maintains a network of 21 observation wells to monitor the natural short- and long-term fluctuations of shallow groundwater levels (i.e., water table conditions) across Illinois. Typically, these wells do not extend into highly productive aquifers; rather, they are constructed in fine-grained glacial materials containing thin lenses of sand. Most are large diameter (>36 inches), dug or bored wells of the type commonly found in areas where shallow, productive aquifers are not present.
These observation wells are purposely located in areas remote from pumping centers in order to minimize the apparent effects of human activities on groundwater levels. Other influences, particularly those of short duration (e.g., less than one day), are of minimal significance under most circumstances. The groundwater levels experienced in these observation wells are thus representative of conditions beneath nonirrigated agricultural land, and of the water levels found in many shallow, rural domestic wells in Illinois.
The locations of the 21 observation wells are shown in figure 2. Most of these wells have been monitored since the early 1960s, and water levels at four current observation wells have been measured since the early 1950s. Each well is equipped with a Stevens Type F continuous water level recorder, which contains a 30-day chart. Therefore each well must be visited monthly so the paper chart on the recorder can be changed. The charts are changed and taped readings of groundwater levels are measured at the end of each month.
Drought Impacts on Well Levels
This network of 21 wells, remote from areas of pumping, was used to assess the impacts of drought on shallow groundwater resources across the state. Illinois experienced five noticeable drought episodes over the last 40 years: 1952-1955, 1963-1964, 1976- 1977, 1980-1981, and 1988-1989. Each impacted both socio-economic and cultural activities in its own way. The droughts of 1963-1964 and 1976-1977 covered a greater geographic area than the droughts of 1980-1981 and 1988-1989 in terms of their impact on shallow groundwater levels statewide (Wehrmann, 1992). Sufficient data were not available for reliable analysis of the groundwater situation during the 1952- 1955 drought.
Lamb et al. (1992) summarized the causes, dimensions, and impacts of the drought of 1988-1989. In regard to ground water, this drought established six new record low groundwater levels in five regions of the state. No other drought event (during the period of record) in Illinois produced this type of historical trend. Figure 2 and table 6 show the network well locations and the historic information associated with these wells, respectively. In addition to the six record lows that were set or tied, groundwater levels were close to the all time record lows at nine additional locations. They were within 1 foot of record lows at five locations and within 2 feet of record lows at four locations.
Comparison of the patterns of accumulated groundwater level departures from normal (for 12-month periods) for the four major drought periods (excluding 1952- 1955) suggests that the magnitude of the accumulated departures for 1988-1989 was greater than for any of the other drought periods. In some instances these departures were more severe for other drought periods, but they were localized to "high-impact" areas of the state where local precipitation was minimal or nonexistent.
Interestingly, for the drought periods of 1963-1964, 1976-1977, and 1988-1989, the greatest accumulated groundwater stage departures all occurred in western and northwestern Illinois. At present, the available data are insufficient to assess precisely why these parts of the state experienced the largest groundwater impacts of drought. Clearly, however, precipitation was deficient in these areas. It is possible that their hydrogeologic systems are especially sensitive to those precipitation deficiencies.
The hydrograph for the Middletown observation well located in central Illinois is presented in figure 3. Records date back to late 1957 for this well, and a record low of 10.5 feet was established in December 1957. The hydrograph for the observation well located in northwestern Illinois near Cambridge (figure 4) in Henry County details water levels since the early 1960s, and shows the full effect of the 1988-1989 drought in this area. The record lows of over 21 feet established in 1988-1989 were more than 2 feet below the previous lows set in 1976-1977. These two hydrographs reveal the severity of the drought of 1988-1989, compared to previous droughts in these two areas.
Based upon available information, the impact of the 1988-1989 drought on ground water persisted substantially longer than the drought's effects on the other components of the hydrologic cycle (precipitation, soil moisture, and surface water).
Groundwater Supply Shortages
Information on shortages in groundwater supplies is available for three drought periods: 1952-1955, 1980- 1981, and 1988-1989. During the 1952-1955 drought, a total of 22 groundwater supply systems experienced shortages (Hudson and Roberts, 1955). Sixteen of these 22 shortages occurred with systems tapping shallow, unconsolidated sand and gravel aquifers. The median depth of these wells was only 40 feet. The 1980-1981 drought was intense only in southern Illinois, a portion of the state where most water supply systems use surface sources. Changnon et al. (1982) do not identify any communities impacted by groundwater shortages.
During the 1988-1989 drought the Environmental Protection Agency monitored 23 communities with potential short-term water deficits due to lowered groundwater levels. But in only eight of these communities was the potential shortage severe enough to require actions to relieve the impacts of drought. New wells were drilled for five of these systems (London Mills, Indianola, Dieterich, Newton, and West Liberty- Dundas). A well repair was required in Edinburg. Water hauling was required for a one month period in Dieterich as a result of pump failure, and Harristown began purchasing water from Decatur. Voluntary conservation measures were adopted in Lincoln and West Liberty-Dundas. In both the 1953-1954 and 1988-1989 drought periods, the number of groundwater systems impacted was considerably less than that for surface water supply systems.
The Illinois State Water Survey constantly receives requests for assistance in evaluating groundwater supplies, and has kept a record of such requests since 1961. Changnon and Easterling (1989) examined the change in the number of requests during three droughts, 1962-1964, 1976-1977, and 1980-1981 and found that during drought conditions, the number of requests increased dramatically. The number of requests for assistance during the 1980-1981 drought was particularly great: 122 percent higher than the average for adjacent years during the most critical six-month period. The average increase in requests during the three droughts analyzed was 82 percent.
Based on the general hydrologic principles of the groundwater budget, the timing of a drought situation is directly related to the impact sustained by the aquifer system, or its ability to recover. If a drought occurs during the recharge season, it will tend to have a greater impact on groundwater levels than a drought that occurs during the growing season. This is opposite to the impact of a summer drought on agriculture, because little groundwater recharge normally occurs during the growing season. Recovery of groundwater levels from storage removals during the growing season is dependent on excess moisture (recharge) during the subsequent late fall and early spring. If recharge does not occur during this time period, groundwater levels will remain low going into the next growing season and will then fall more rapidly as ground water is taken out of storage by evapotranspiration and groundwater runoff.
Recharge to many of the deep aquifers is limited to slow leakage through the drift. To this end, recharge to deep aquifers is buffered from short-term irregularities in precipitation by the lag time required for reaction to drought conditions. The needed recharge of these systems during nondrought periods is typically sufficient to return them to their previous levels. Currently, the use of groundwater resources to supplement surface water shortages during drought situations is an effective, short-term solution in dealing with a drought condition.
Lack of precipitation is not generally recognized as the underlying cause of groundwater shortages until the resource has declined to a noticeable extent. In recent years, and to some degree now, communities that depend upon ground water often believe that they "run out" of water essentially overnight. Yet a program of regular measurements of depth to water in their wells would alert responsible officials long before the emergency arises (Changnon et al., 1982).
Water Conservation during Drought
Drought plays an important role in prompting water users to secure adequate reserves from alternate sources. The impacts of a drought situation are a strong incentive to develop emergency planning systems to defer the impacts on existing water resources. In 1989, the Illinois Water Inventory Program expanded its Water Use Survey to include questions pertaining to water conservation programs imposed during the drought of 1988. Following are the results of this survey taken from an open file report (Kirk, 1989). This survey indicated that 23.5 percent of the 1,396 public water supplies returning questionnaires requested or imposed water conservation practices in 1988. That is, 21.2 percent of the state's population, or more than 2.47 million people were asked to restrict their water use during this drought year.
For public water supplies not using Lake Michigan water allocations, 1,349 questionnaires were returned out of 1,741 (77.5 percent). These public water supplies reported supplying 3.67 million people with potable water out of the 4.27 million people served by public water supplies without Lake Michigan water allocations (85.9 percent). Of the 1,349 responding facilities, 1,094 responded to the drought questions (81.8 percent). Water conservation was imposed or requested by 22.7 percent of the public water supplies (306), affecting 1.18 million people or about 27.6 percent of the state's population outside of those using Lake Michigan water allocations. Of those affected by the drought, 56.4 percent rely on ground water as their sole source of water.
Of those using water conservation in 1988, 47.0 percent indicated it was due to limited water availability, 14.4 percent indicated limited treatment or distribution capacity, and 38.9 percent listed other causes. The most often restricted water use was lawn watering, followed by water conservation and car washing.
Water conservation practices were reported successful by 40 percent of all public water supplies that used them. For the public water supplies that responded to the question about the success of their conservation efforts, 92.5 percent reported success. The success of these conservation measures ranged from 0 to 49 percent reduction in water use and the total quantity of water saved, where reported, ranged from 0 to 1.5 million gallons per day. Future plans to expand the public water supplies were indicated by 38.6 percent of those using water conservation measures and 8.9 percent of those without restrictions. Of these, 48.3 percent planned to increase their supply, 16.9 percent planned to increase treatment, and 9.3 percent planned to increase distribution capabilities.
Of the responding public water supply facilities with Lake Michigan water allocations, 11.3 percent asked their users to conserve water, representing 17.5 percent of the approximately 7.37 million people served. Including the 47 public water supplies with Lake Michigan water allocations that responded to the survey, at least 21.2 percent of the state population was asked to conserve water in 1988, totaling about 2.47 million people.
Illinois has experienced five drought periods over the past 40 years: 1952-1955, 1963-1964, 1976-1977, 1980-1981, and 1988-1989. Each situation created impacts, some major, in both the physical and/or socioeconomic spheres. With each drought, lessons are learned and steps taken to reduce the impact of future droughts. However, severe droughts are very infrequent, and over time water supply systems can develop problems associated with aging facilities, reservoir sedimentation, and increases in water use. A number of facilities, using both surface and groundwater sources, are still not adequate to survive a 50-year drought.
Drought situations impact a large percentage of the state's population and the surface and groundwater resources within the state. Understanding the conditions that produce drought or cause drought conditions may allow us to develop better strategies to help eliminate or reduce its impact. Yet at this point it is apparent that the occurrences of drought still catch us off-guard, and that mitigative measures typically are not begun until the drought impacts become obvious. References
Broeren, S.M., and K.P. Singh. 1989. Adequacy of Illinois Surface Water Supply Systems to Meet Future Demands. Illinois State Water Survey Contract Report 477, Champaign, IL.
Changnon, S.A. 1980. Removing the Confusion over Droughts and Floods: The Interface between Scientists and Policy Makers. Water International 10:10-18.
Changnon, S.A. 1989. The 1988 Drought, Barges, and Diversion. Bulletin of the American Meteorological Society 70(9):1092-1104.
Changnon, S.A., G.L. Achtemeier, S.D. Hilberg, H.V. Knapp, R.D. Olson, W.J. Roberts, and P.G. Vinzani. 1982. The 1980-1981 Drought in Illinois: Causes, Dimensions, and Impacts. Illinois State Water Survey Report of Investigation 102, Champaign, IL.
Changnon, S.A., and W.E. Easterling. 1989. Measuring Drought Impacts: The Illinois Case. Water Resources Bulletin 25(1):27-42.
Changnon, S.A. et al. (17 co-authors). 1987. Droughts in Illinois: Their Physical and Social Dimensions. Illinois State Water Survey Report to the Illinois Department of Energy and Natural Resources, Champaign, IL.
Gerber, W.D. 1932. The Drought of 1930 and Surface Water Supplies in Illinois. Journal of the American Water Works Association 24(6): 840. Hudson, H.E., and W.J. Roberts. 1955. The 1952-1955 Illinois Drought with Special Reference to Impounding Reservoir Design. Illinois State Water Survey Bulletin 43, Champaign, IL.
Huff, F.A., and S.A. Changnon. 1963. Drought Climatology of Illinois. Illinois State Water Survey Bulletin 50, Champaign, IL.
Kirk, J.R., 1989. Illinois Public Water Supplies' Response to the Drought of 1988. Unpublished manuscript, Illinois State Water Survey, Champaign, IL.
Knapp, H.V. 1990. Kaskaskia River Basin Streamflow Assessment Model: Hydrologic Analysis. Illinois State Water Survey Contract Report 499, Champaign, IL.
Koellner, W. 1988. Climate Variability and the Mississippi River. In M.H. Glantz (ed.), Societal Responses to Regional Climate Change, Forecasting by Analogy. Westview Press, Boulder CO.
Lamb, P.J. (ed.) et al. (14 co-authors). 1992. The 1988- 1989 Drought in Illinois: Causes, Dimensions, and Impacts. Illinois State Water Survey Research Report 121, Champaign, IL.
Riebsame, W.E., Changnon, S.A., and T.R. Kal. 1991. Drought and Natural Resources Management in the United States. Westview Press, Boulder, CO.
Wehrmann, H.A. 1992. Groundwater Conditions. In The 1988-1989 Drought in Illinois: Causes, Dimensions, and Impacts. Illinois State Water Survey Research Report 121, Champaign, IL.
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