Indiana regional water studies

By: Ted Schurter
August 18, 2026

The Indiana Finance Authority’s two recent regional water studies, the North Central Indiana and Wabash Headwaters, explain the location, origin and extent of those regions’ water resources.

They detail the historic and current levels of water availability, excess water availability and cumulative excess water availability for each region, and the subbasins within, and estimate how those metrics may change based on future conditions.

Understanding these concepts and water availability metrics should make interpreting the statewide water assessment Indiana Gov. Mike Braun ordered completed by the end of 2026 a little easier.

Map showing combined area of North Central Indiana, shaded light blue, and Wabash Headwaters, shaded darker blue, water studies by the Indiana Finance Authority. A smaller inset map of Indiana shows their state context.

Each study encompasses a region that is divided into subbasins. Their boundaries are delineated by hydrology, topographic features, and measured streamflow data, not by administrative boundaries like county or state lines.

Each subbasin drains a specific area, that is the water within it generally flows to a common point, where the streamflow data is measured.

For each subbasin, water availability is calculated with a formula:

Water availability =
Net natural baseflow – net minimum instream flow requirement + subbasin net reservoir release.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority and the subbasins within them marked by gold lines. An inset map in the upper left shows the study areas in the context of the state of Indiana.

Water availability =
Net natural baseflow – net minimum instream flow requirement +subbasin net reservoir release.

Net natural baseflow is the total groundwater contribution to streamflow within a subbasin. This is estimated without human influences like water withdrawals or wastewater-return flows.

The net minimum instream flow requirement is the amount of water that must remain within a subbasin to maintain ecosystem health, water quality and recreational use.

Like baseflow and precipitation, the minimum instream flow requirement changes seasonally.

Adjust the slider to see how wet or dry conditions, combined with the minimum instream flow requirement, affect water availability.

Illustration of a cylinder with dark blue water and a fixed dashed gray line at the bottom labeled 'Instream flow requirement.' An indicator and label show Natural baseflow on the left and a bracked indicator showing Water availability on the right. Both labels move up and down when users activate the slider control to show relationship between baseflow, the instream flow requirement and water availability.

Water availability: baseflow

Natural baseflow originates from aquifers so understanding their relationship to the subbasins above them is important.

An aquifer is any collection of geologic material that is saturated with enough water to yield significant amounts of it to springs or wells.

They may be consolidated — more solid formations cemented together by weight and time — or unconsolidated — comprised of looser material like sand and gravel.

Indiana is underlain by four principal aquifers, the designation the US Geological Survey (USGS) gives to aquifers that serve as primary water supply sources in a region.

Three of the four principal aquifers in Indiana are consolidated aquifers, sometimes called bedrock aquifers.

The two largest are comprised of carbonate rock, and sandstone and carbonate rock.

The third, a sandstone aquifer along the Ohio River, makes only minor contact with Indiana.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority and two principal aquifers. The carbonate-rock is shaded magenta, the sandstone and carbonate rock is shaded green. An inset map in the upper left shows the study areas in the context of the state of Indiana.

Water availability: baseflow

While principal aquifers are the most productive, Indiana is underlain by many aquifers of varying productivity and depth. Many of the bedrock aquifer systems stretch across wide swaths of the state.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority and bedrock aquifers within Indiana shaded in different colors: Blue River, Sanders Groups; Borden Group; Carbondale Group;Coldwater, Ellsworth, Antrim Shales; Maquoketa Group; McLeansboro Group; New Albany Shale; Raccoon Creek Group; Silurian and Devonian Carbonates. An inset map in the upper left shows the study area and the aquifers in the context of the state of Indiana.

Water availability: baseflow

Indiana's unconsolidated aquifers are generally closer to the surface and geologically newer than their consolidated counterparts.

The state has mapped their yields where data is available. They are a common source for domestic wells throughout the state and study area.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority as a choropleth with light shades of blue representing low domestic well range average of 0 gallons per minute capacity transitioning to darker blue capacity of 50 gallons per minute. An inset map in the upper left shows the study area and the aquifer capacities in the context of the state of Indiana.

Water availability: baseflow

They also support high-capacity withdrawals. Higher yields are found in the northern portions of the state and study area.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority as a choropleth with light shades of blue representing low domestic well range average of 150 gallons per minute capacity transitioning to darker blue capacity of 1,500 gallons per minute capacity. An inset map in the upper left shows the study area and the aquifer capacities in the context of the state of Indiana.

Water availability: baseflow

The unconsolidated glacial aquifer system sprawls across much of the state and beyond. It is the largest water source for public supply and self-supplied industrial of any principal aquifer, according to the USGS.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority and the principal glacial aquifer shaded in teal. An inset map in the upper left shows the study area and the aquifer in the context of the state of Indiana.

Water availability: baseflow

Groundwater and surface water interact throughout the hydrologic cycle. Sometimes surface water is lost to groundwater recharge. At others times, groundwater from aquifers contributes volume to surface water sources like rivers or streams.

This relationship is not hard to imagine when the state’s rivers and streams are overlaid atop the glacial aquifer system.

It is through these baseflow contributions, not their total water capacity, that aquifers impact water availability calculations in these studies.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority and the principal glacial aquifer shaded in teal. Major and minor waterways are also shown in dark and light blue resepectively. An inset map in the upper left shows the study area and the aquifer and the waterways in the context of the state of Indiana.

Water availability =
Net natural baseflow – net minimum instream flow requirement + subbasin net reservoir release.

Reservoirs influence water availability by storing or releasing water within a subbasin.

During wet seasons, water that would otherwise be measured at the subbasin outlet is stored instead, reducing seasonal water availability, sometimes to negative values.

When released, it artificially raises water availability higher than it would otherwise be, a tactic that can help preserve stream and river flow in dry seasons.

Three reservoirs were identified in each study that influence the seasonality of water availability in their subbasins and their downstream counterparts.

Set the natural baseflow slider and then adjust the reservoir operations slider to see how reservoir storage or release impacts water availability.

Illustration of a cylinder with dark blue water and a fixed dashed gray line at the bottom labeled 'Instream flow requirement.' An indicator and label show Natural baseflow on the left and a bracked indicator showing Water availability on the right. Both labels move up and down when users activate the slider control to show relationship between baseflow, the instream flow requirement and water availability. At high natural baseflow levels, the top of the cylinder will adjust up to accomodate more water when the Reservoir operations slider moves toward Releasing water.

Excess water availability

Once the natural baseflow has been calculated, reservoir operations accounted for, and the minimum instream flow requirements met, excess water availability can be determined using another formula:

Excess water availability =
Water availability – water withdrawals + return flows.

Water withdrawals occur when groundwater is pumped from aquifers or surface water is drawn from sources like lakes, rivers or streams.

The state of Indiana requires facilities that extract more than 100,000 gallons a day of ground or surface water to register with the state.

These registered withdrawals are identified by their origin — ground or surface — and categorized by end-use such as public supply, irrigation, industrial and others.

Aside from energy production, most withdrawals in the study areas come from groundwater.

Use the button to visualize how many of Indiana's significant groundwater withdrawal facilities are found within the principal glacial aquifer boundaries.

Map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority and the locations of significant groundwater withdrawal facilities indicated with circles proportional to the gallons per minute they are capable of withdrawing ranging from 200 gallons per minute to 13,500. The colors correspond to the end-use for the withdrawn water. They include energy, industry, irrigation, miscellaneous public supply and rural use. A button toggles the visibility of the principal glacial aquifer shaded in teal. An inset map in the upper left shows the study area and withdrawal facilities in the context of the state of Indiana.

Excess water availability =
water availability – water withdrawals + return flows.

Water withdrawals vary by amount, season, source, subbasin and intended use but they all reduce the amount of water available in the subbasin where they occur.

Subbasins with energy production facilities may have high surface water withdrawals from lakes connected to power plants leading to more consistent year-round demand. In contrast, a subbasin with high irrigation levels may experience more seasonal withdrawal variability.

Compared to natural baseflow, water withdrawals are a small component of water availability.

Adjust the slider to determine how much water is withdrawn from the example subbasin. For illustrative purposes their impact is exaggerated.

Illustration of two cylinders with dark blue water. The larger cylinder is labeled ‘Water within subbasin’ and includes a fixed dashed gray line at the bottom labeled 'Instream flow requirement' a bracketed indicator showing ‘Available water’ on the left. A line with an arrow connects the larger cylinder to a smaller one in the upper left labeled ‘Water withdrawals.’ The level in each cylinder changes relative to the Water withdrawals slider position. Moving the slider to Low withdrawals decreases the blue water level in the small cylinder and increases it in the larger. Moving the slider to High withdrawals increases the level in the small cylinder and decreases it in the larger.

Excess water availability =
water availability – water withdrawals + return flows.

Water withdrawals can be divided into consumptive and non-consumptive use.

Non-consumptive use returns withdrawn water back to the subbasin.

Water withdrawn for coal-based energy production is considered 99% non-consumptive. Nearly all the water is returned to the subbasin after use.

Water withdrawn for irrigation, on the other hand, is considered 80% consumptive. Most of the water is lost to evapotranspiration and does not return to the subbasin.

The percent of consumptive use varies by subbasin and season based on the type of use and other factors.

Illustration of two cylinders with dark blue water. The larger cylinder is labeled ‘Water within subbasin’ and includes a fixed dashed gray line at the bottom labeled 'Instream flow requirement' a bracketed indicator showing ‘Available water’ on the left. A line with an arrow connects the larger cylinder to a smaller one in the upper left labeled ‘Water withdrawals.’ The upper cylinder has additional water in a light blue shade and a label to the right indicating the percentage of ‘Non-consumptive use.’ The percentage amount is randomly generated and updated automatically.

Excess water availability: return flows

The net return flows are the portion of non-consumptive water withdrawals that return to the subbasin. They can be highly seasonal and can exceed the amount of natural baseflow during very dry seasons.

Illustration of two cylinders with dark blue water. The larger cylinder is labeled ‘Water within subbasin’ and includes a fixed dashed gray line at the bottom labeled 'Instream flow requirement' a bracketed indicator showing ‘Available water’ on the left. A line with an arrow connects the larger cylinder to a smaller one in the upper left labeled ‘Water withdrawals.’ The upper cylinder has additional water in a light blue shade and a label to the right indicating the percentage of ‘Non-consumptive use.’ The percentage amount is randomly generated and updated automatically. A dashed line in the same light blue color as the non-consumptive use water connects the smaller cylinder in the upper left to the larger cylinder and is labeled ‘Return flows.’

Excess water availability: return flows

The net returns are added to the available water after the withdrawals are accounted for to determine excess water availability.

Illustration of two cylinders with dark blue water. The larger cylinder is labeled ‘Water within subbasin’ and includes a fixed dashed gray line at the bottom labeled 'Instream flow requirement' a bracketed indicator showing ‘Available water’ on the left and another bracketed indicator labeled ‘Net returns’ that denotes another water level shaded in light blue directly above the darker blue ‘Available water.’ A bold label that says ‘Excess water availability’ on the right side of the cylinder with brackets that include entire depth of both water levels. A line with an arrow connects the larger cylinder to a smaller one in the upper left labeled ‘Water withdrawals.’ The upper cylinder has additional water in a light blue shade and a label to the right indicating the percentage of ‘Non-consumptive use.’ The percentage amount is randomly generated and updated automatically. A dashed line in the same light blue color as the non-consumptive use water connects the smaller cylinder in the upper left to the larger cylinder and is labeled ‘Return flows.’

Cumulative excess water availability

Half of the 26 subbasins in the combined study area receive contributions from at least one upstream subbasin.

These contributions are what distinguish cumulative excess water availability. It utilizes cumulative versions of the variables used to calculate excess water availability by incorporating contributions from upstream basins when applicable.

The cumulative excess water availability of the furthest downstream basin in each study area represents that region's cumulative excess water availability.

For the Wabash Headwaters that is subbasin 10; for the North Central Indiana study, and the combined study area, that is subbasin 16.

Map showing combined area of North Central Indiana, shaded dark blue, and Wabash Headwaters, shaded light blue, water studies by the Indiana Finance. The opacity of subbasins that do not have contributing upstream subbasins is reduced to de-emphasize them. Wabash Headwaters subbasin 10 and North Central Indiana subbasin 16 are labelled because they represent the place where the cumulative excess water availability for their collective region is determined. An inset map in the upper left shows the study area in the context of the state of Indiana.

Cumulative excess water availability

Without upstream contributions, a subbasin's cumulative excess water availability is equal to its excess water availability.

Illustration of a cylinder labeled ‘Subbasin’ with two sections: dark blue water and lighter blue water. The cylinder has a dashed gray line near the bottom labeled ‘Instream flow requirement’ that marks the division between the dark and light blue waters. There are two brackets of identical size on the left and right of the cylinder labeled ‘Excess water availability’ on the left side and ‘Cumulative excess water availability’ on the right side.

Cumulative excess water availability

A subbasin that receives water from an upstream subbasin adds that excess water availability to its own to determine its cumulative excess water availability.

Illustration of a cylinder labeled ‘Subbasin’ with two sections: dark blue water and lighter blue water. The cylinder has a dashed gray line near the bottom labeled ‘Instream flow requirement’ that marks the division between the dark and light blue waters. A smaller, similar cylinder appears in the upper left labeled ‘Upstream subbasin’ with an ‘Excess water availability’ label at the top of its light blue water level. A light blue dashed line connects the two cylinders with an arrow pointing to the ‘Subbasin’ cylinder. The light blue water level in the ‘Subbasin’ cylinder rises above the ‘Excess water availability’ bracket, and a second, larger bracket labeled ‘Cumulative excess water availability’ spans the added height.

Cumulative excess water availability

A subbasin with many upstream contributions will generally have higher cumulative excess water availability than a subbasin with fewer upstream contributions.

Illustration of a cylinder labeled ‘Subbasin’ with two sections: dark blue water and lighter blue water. The cylinder has a dashed gray line near the bottom labeled ‘Instream flow requirement’ that marks the division between the dark and light blue waters. There are two brackets on the left and right of the cylinder labeled ‘Excess water availability’ on the left side and ‘Cumulative excess water availability’ on the right side. A smaller, similar cylinder is in the upper left labeled ‘Upstream subbasin’ with an ‘Excess water availability’ label on the right side at the top of the light blue water level. A trio of smaller similarly constructed cylinders is in the upper right. Light blue dashed lines connect the accessory cylinders with an arrow pointing to the primary ‘Subbasin’ cylinder. The light blue water level in the 'Subbasin' cylinder now exceeds the 'Excess water availability' level that is not denoted at its top with an additional dashed line across the cylinder. The bracket for the 'Cumulative excess water availability' has adjusted to match the changed level of the light blue water line.

Cumulative excess water availability

The impacts of upstream contributions on downstream subbasins, and seasonal variation, are evident in the studies' estimates of historic and future cumulative water availability by season and subbasin.

The historic period averages seasonal data from 2007 to 2022 while the future projection reflects estimates for the 2060s.

Faceted choropleth map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority with their subbasins defined by dark lines and shaded in a range of green colors to indicate cumulative excess water availability in millions of gallons daily. The range is 12-498 on the low end and 7,727 – 9,964 on the highest end. The facet is made of two columns - Historic and Future, and four rows – Winter, Spring, Summer, Fall. The furthest downstream subbasins show the highest totals across the seasons with Future Spring showing the highest totals.

Cumulative excess water availability

On average, the studies' authors expect wetter springs and drier falls to contribute to region-wide reductions and surpluses relative to historic conditions in the spring and fall.

Diverging color faceted choropleth map showing combined area of North Central Indiana and Wabash Headwaters water studies by the Indiana Finance Authority with their subbasins defined by dark lines and shaded in a range of brown to blue-green colors to indicate the percent change in cumulative excess water availability across the four seasons between historic conditions and projected future conditions. The lightest colors, including white in the middle of the scale, indicate little to no change. Darker colors indicate higher change. Brown colors indicate negative change while blue-green colors indicate positive change.

Cumulative excess water availability

Not every year is average, though.

An exceedance curve visualizes how often a certain value is exceeded within a time frame. They are useful for understanding how extremely wet or dry conditions impact water availability metrics.

In North Central Indiana subbasin six, spring has the highest cumulative excess water availability.

In the future, the study projects cumulative excess water availability of about 6,000 million gallons daily under the wettest conditions, those exceeded six percent of the time. Average conditions, exceeded about half the time, would be 3,600 million gallons. The driest conditions, exceeded 94% of the time, would see about 1,200 million gallons daily.

Both summer and winter experience negative water availability during the driest conditions in the subbasin.

Line chart showing Future cumulative excess water availability exceedances for North Central Indiana Regional Water Study subbasin 6. Four colored lines correspond to four seasons: spring-blue, summer-brown, fall-orange, winter-light blue. The y axis is millions of gallons daily and ranges from 0 to 6,000. The x axis shows exceedance percentage of 0 to 100 from left to right. Three points with labels mark the two extremes and the middle of the Spring line: “Extremely wet: 6%”, “Average conditions: 53%”, “Extremely dry: 94%.”

Cumulative excess water availability

The cumulative excess water availability values can also be visualized by their area at their highest, lowest and average exceedance values and color coded to represent conditions:

• extremely wet
• average
• extremely dry

Line chart showing Future cumulative excess water availability exceedances for North Central Indiana Regional Water Study subbasin 6. Four labeled lines correspond to four seasons: spring, summer, fall and winter; the spring line is blue, the others shades of gray. The y axis is millions of gallons daily and ranges from 0 to 6,000. The x axis shows exceedance percentage of 0 to 100 from left to right. Three points with labels mark the two extremes and the middle of the Spring line: “Extremely wet: 6%”, “Average conditions: 53%”, “Extremely dry: 94%.” The points are connected via lines with arrows at each end to shaded squares arranged in vertically on the right side of the chart representing the area of value on the y axis and color coded. Light peach is extremely wet, orange is average and red is extremely dry.

Cumulative excess water availability

These can be consolidated into a single element for easier comparisons across a season's possible climate conditions and...

• extremely wet
• average
• extremely dry

Line chart showing Future cumulative excess water availability exceedances for North Central Indiana Regional Water Study subbasin 6. Four labeled lines correspond to four seasons: spring, summer, fall and winter; the spring line is blue, the others shades of gray. The y axis is millions of gallons daily and ranges from 0 to 6,000. The x axis shows exceedance percentage of 0 to 100 from left to right. Three points with labels mark the two extremes and the middle of the Spring line: “Extremely wet: 6%”, “Average conditions: 53%”, “Extremely dry: 94%.” The points are connected via lines with arrows at each end to shaded squares on the right side of the chart representing the area of value on the y axis and color coded. Light peach is extremely wet, orange is average and red is extremely dry. The three squares overlap each other in the upper right corner of the chart.

Cumulative excess water availability

...to make it easy to compare the impact of different climate conditions across the four seasons.

The occasional negative water availability that occurs in some subbasins during summer, fall and winter is visualized as an empty, white square.

• extremely wet
• average
• extremely dry

Line chart showing Future cumulative excess water availability exceedances for North Central Indiana Regional Water Study subbasin 6. Four labeled lines correspond to four seasons: spring, summer, fall and winter. The y axis is millions of gallons daily and ranges from 0 to 6,000. The x axis shows exceedance percentage of 0 to 100 from left to right. Three points with labels mark the two extremes and the middle of the Spring line: “Extremely wet: 6%”, “Average conditions: 53%”, “Extremely dry: 94%.” There is a 2 by 2 grid of boxes, each made of three boxes stacked atop each other that represent the high, low and average exceedance values for each season. Light peach is extremely wet, orange is average and red is extremely dry. A label identifies the white squares that indicate negative cumulative excess water availability.

Cumulative excess water availability

Upstream contributions, especially in subbasins through which the Wabash River flows, magnify the amount of cumulative excess water availability, especially compared to subbasins with few or no upstream contributions.

But even those subbasins aren’t immune from the reductions that accompany extremely dry conditions in the winter, summer and fall.

*Location of NCI subbasins 11 and 12 charts are shifted to accomodate chart placement.

Map titled ‘Future cumulative excess water availability by season, subbasin and climate conditions’ showing combined area of North Central Indiana, shaded dark blue, and Wabash Headwaters, shaded light blue, water studies by the Indiana Finance Authority. For each subbasin, four stack’s of three squares each are arranged in a grid representing clockwise from top left winter, spring, summer and fall. Each season has three boxes stacked within each other, the color of which denotes the volume of cumulative excess water availability under either extremely wet (peach color), average (orange color), or extremely dry (red color) conditions. Each of the subbasin grids includes a shape denoting the water study: a square for the North Central Indiana study and a circle for the Wabash Headwaters study. The shapes are arranged in a key labeled ‘Downstream basin flow’ in the lower right to show which subbasins have upstream contributions and which, shaded dark blue, represent the main stem of the Wabash River.

Recomendations

A few themes emerged from the studies’ detailed recommendations:

• Decrease demand:
• Implement water loss prevention programs and infrastructure improvements and updates
• Promote conservation through public campaigns, incentives and regulations
• Increase supply:
• Consider conjunctive water use that incorporates both surface and groundwater to meet demands
• Exploration and development of groundwater sources
• Reassess reservoir storage and allocation; explore non-reservoir storage potential
• Improve data:
• Increase data monitoring, collection and sharing for water quality and quantity
• Refine analysis methods

*Location of NCI subbasins 11 and 12 charts are shifted to accomodate chart placement.