Streams, rivers, and lakes are an important part of the landscape, as they provide water supply, recreation, and transportation for humans, and a place to live for a variety of plants and animals. Groundwater also is an important water resource that serves as a source of drinking water for more than 140 million people in the United States.
In some areas, contamination from natural and human sources has affected the use of surface water and groundwater. For example, naturally occurring minerals within bedrock can impair the taste of groundwater and in some cases limit its use. The spilling, leaking, improper disposal, or intentional application of chemicals at the land surface can result in runoff that contaminates nearby streams and lakes, or infiltration that contaminates underlying aquifers and water wells.
The Upper Iroquois Watershed is drained by the Iroquois River and its tributaries. The Iroquois River flows westward and empties into the Kankakee River in Illinois. There are no large lakes within the watershed, only a few man-made ponds, filled quarries, and backwater areas which are scattered throughout the watershed.
The hydrology and groundwater function of the Iroquois River is unique to Indiana. The upper reaches of the watershed north of Rensselaer are dominated by pockets of sand and muck that tend to slow flows downstream. Closer to Rensselaer, the hydrology of the watershed becomes more defined and the typical clay till found in much of Indiana becomes the controlling soil type (Banning Engineering, P.C., 2010).
Residents living in the Iroquois watershed get their potable water from deep wells that have been drilled into unconfined aquifers comprised of unconsolidated sand and gravelly sand or confined aquifers located in Silurian, Devonian, and Mississippian age carbonate bedrock. Factors that can affect the movement of contaminants from surface water sources to water wells are the chemical nature of the contaminant(s), the physical properties of the soil and aquifer material, the amount and timing of recharge, and the direction and velocity of groundwater movement.
Four primary consolidated aquifer subsystems lie within the Upper Iroquois Watershed.
The Borden Bedrock Group lies primarily south of U.S. Highway 24. It consists mostly of gray argillaceous siltstone and shale. Some fine-grained sandstone and some minor interbedded discontinuous lenses of limestone are also present in this region. Aquifer thickness ranges from 0 to 800 feet and typically yields 1 to 10 gallons per minute with significant drawdown.
- The New Albany Shale Group lies, for the most part, between U.S. Highway 24 and Indiana State Road 16. It consists of black and greenish gray shale ranging from 0 to 340 feet in thickness. It commonly yields 1 to 10 gallons per minute.
- The Silurian and Devonian Carbonates Group lies in the northern part of the watershed. This group is predominantly carbonate rock units (limestone and dolomite) with some interbedded shale units. It is difficult to distinquish between the bedrock materials and therefore this unit is considered as a single water-bearing system. Aquifer thickness ranges from 0 to 1,000 feet and typically yields 10 to 25 gallons per minute with yields decreasing southward.
- The Kentland Anomaly Aquifer System is confined to a relatively small area in Newton County. The system is located just east of Kentland and is adjacent to the border of Benton County. The bedrock in this area has been faulted and folded by undetermined forces that brought deeply buried Ordovician rocks, consisting mostly of sandstone and carbonates, to the bedrock surface. Bedrock in this area also includes the Borden Group, the New Albany Shale Group, Silurian and Devonian Carbonates, and Pennsylvanian age rocks consisting of the Raccoon Creek Group which is composed mostly of sandstone and shale with minor amounts of mudstone, coal, and limestone. Aquifer characteristics in this area are unknown because of the area’s small size and extremely limited number of registered groundwater withdrawal facilities. This system has a moderate susceptibility to surface contamination because the bedrock is highly fractured and the surface materials that overly the system are relatively thin.
There are three primary unconsolidated aquifer subsystems within the watershed.
1. The Iroquois Valley Subsystem lies adjacent to the Iroquois River and west of Interstate 65. It consists of intertill sand and gravel within a buried bedrock valley. Aquifer thickness is commonly 5 to 20 feet but ranges from 3 to 40 feet. It typically yields 10 to 40 gallons per minute.
2. The Iroquois Basin Subsystem lies within the southern portion of the watershed. It consists of isolated surface sands, thin intertill sand and gravel and some deeply buried aquifers in buried valleys. Aquifer thickness is commonly 2 to 3 feet and yields 4 to 20 gallons per minute.
3. The Iroquois Moraine Subsystem lies along the northern edge of the watershed. It consists of isolated and discontinuous intertill sand and gravel. Aquifer thickness typically ranges from 3 to 25 feet in thickness and yields 4 to 10 gallons per minute.
Geological bedrock determines the slope of a watershed basin and its drainage patterns. This can influence how surface water moves through the watershed, have an impact on flooding/flashiness, and have an effect on groundwater recharge. Topography throughout the Iroquois Watershed can be characterized as relatively flat to gently rolling with inter-dispersed depressional areas and sand ridges which rise a few feet above the general ground level. Narrow, steep slopes can be found in some areas adjacent to the Iroquois River and some of its tributaries.
The difference between the highest elevation and the lowest elevation in a watershed is defined as topographic relief. Topographic relief of a watershed’s landscape and gravity influence stream velocity and discharge, stream flow direction, watershed drainage, and creation of watershed divides, streambed composition, and ultimately, the water quality parameters in a stream. For example, areas with rugged topography may be more subject to erosion due to runoff. The steeper surfaces are a vehicle for faster water flow. This in turn, can cause more widespread erosion, depositing sediment into lakes and streams
Elevations in the upper reaches of the watershed are approximately 710 feet above sea level. The lower reaches near the Indiana/Illinois State Line are near 625 feet. The average elevation is about 655 feet above sea level (Rogers, 1955). The highest elevation in the watershed is about 770 feet above sea level and can be found near the intersection of Benton, Jasper and Newton Counties. In Jasper County this elevation is located southwest of Remington in the southwest corner of Section 32 in Carpenter Township. In Newton County the highest point is located southeast of Goodland in the southeast corner of Section 36 in Grant Township.
There are approximately 55 miles between the upper reaches of the watershed and the Indiana/Illinois border. Average slope of the watershed is approximately 1.5 feet per mile (Banning Engineering, P.C., 2010).