The Indiana Water Balance Network
by:
Shawn Naylor and Andrew R. Gustin
Climate change with its associated droughts and floods highlight the need to improve our understanding of
water budgets in Indiana. During dry periods, precipitation is reduced and the hydrologic cycle shifts into a
deficit phase (think of the state's water budget during droughts like the national debt). Water is lost from the
landscape due to several processes such as transpiration and evaporation. Alternatively, during wet
periods when rainfall is excessive, hydrologic components such as soil moisture become important
because they directly influence the timing and duration of flooding. With these concerns in mind, personnel
at the Center for Geospatial Data Analysis at the Indiana Geological Survey (CGDA/IGS) developed the
Indiana Water Balance Network (IWBN) to monitor trends in water loss and gain for different components
of the hydrologic cycle (fig. 1).
Hydrologic budget equation
For a particular watershed, water balance can generally be viewed in terms of inputs and outputs, with the
primary input, precipitation (P), balanced by processes that “consume” water. The following general
hydrologic budget equation is from Freeze and Cherry (1979), and the subsequent text describes each
component:
Figure 1. Diagram showing major surface and atmospheric components of the
hydrologic cycle (Source: National Atmospheric and Oceanic Administration).
P = Q + E + ΔSS + ΔSG
Precipitation (P)
Rain, snow, hail, sleet, and drizzle combined are precipitation inputs to the hydrologic cycle. The National
Climatic Data Center (NCDC) lists approximately 150 stations in Indiana where precipitation is measured.
However, owing to the extreme variability of precipitation across the landscape, additional monitoring sites
are always warranted. Precipitation is measured using a tipping bucket rain gage at each of the IWBN
sites.
Runoff (Q)
Rainfall that is diverted toward streams and contributes to stream discharge is called “runoff”. This
Figure 2. Diagram showing varying groundwater flow path lengths with their
origin (recharge area) and destination (discharge area or pumping well)
(Winter and others, 1998).
parameter is also difficult to measure, but it can be estimated based on stream flow measurements at a
particular spot in the watershed. Streamgages ( see USGS website for more information) are sites along
streams and rivers where stream flow is measured, and these monitoring sites are vital for both flood
forecasting and determining watershed runoff.
Evapotranspiration (E)
Moisture leaves the Earth's surface to the atmosphere via evaporation and transpiration (loss of water from plants). The combined processes are called
“evapotranspiration” and this is one of the most difficult parameters of the hydrologic cycle (fig. 1) to measure. A number of weather-related variables (such as solar and
atmospheric radiation, wind speed, and relative humidity) are measured and used to compute potential evapotranspiration (PET, the maximum amount possible given the
existing conditions). The IWBN uses guidelines developed by the Food and Agriculture Organization of the United Nations (Allen and others, 1998) to calculate PET.
Soil Moisture (ΔSS )
Precipitation that infiltrates the ground surface and
remains in pore spaces within the soil profile is called
“soil moisture”. Upward water movement occurs when
plant roots extract soil moisture and also when capillary
forces bring moisture closer to the surface, making it
susceptible to evaporation. Alternatively, downward
movement of soil moisture toward the saturated zone
(below the water table) results in groundwater
recharge. Both these processes can result in movement
of water out of the soil storage component.
Soil-moisture sensors measure volumetric water
content continuously at eight IWBN sites with two sites
collecting shallow data (upper 2 ft) and six sites
collecting data from 1 ft to 6 ft below the ground
surface at 1-ft intervals.
surface at 1-ft intervals.
Groundwater recharge/discharge (ΔSG )
Groundwater recharge and discharge are dependent
upon the geology of an area, but groundwater recharge
generally occurs near watershed boundaries, while
discharge occurs in valleys near streams (fig. 2). It is
important to identify areas of focused recharge,
because these are settings where aquifers are
particularly sensitive to contamination. Current research
Figure 3. Interactive map displaying locations of IWBN monitoring sites.
at the CGDA/IGS is focused on using groundwater flow
models to determine locations and rates of groundwater recharge. Furthermore, two IWBN monitoring sites are currently collecting matric potential (measure of how
tightly water is held in pore spaces), soil moisture, and groundwater level data such that wetting/drying conditions, water fluxes, and water-table rise can be determined
respectively.
Overview
Several projects undertaken at the CGDA/IGS resulted in the collection of continuous data related to the water balance (Table 1). Seven sites have data that can be
viewed online; and you can contact Shawn Naylor ([email protected]) to obtain data for the remaining sites.
Site Name
Data Link
County
Geologic Setting
P
E
ΔSS
ΔSG
(click name)
Flat Rock River
Y
Rush
Alluvial terrace
Y
Y
Y
Y
Bradford Woods
Y
Morgan
Alluvial terrace
Y
Y
Y
Y
Shelbyville Moraine
Y
Fayette
Moraine crest
Y
Y
Y
Y
Eel River Valley
Y
Allen
Outwash terrace
Y
Y
Y
Y
Wabash Moraine
Y
Allen
Moraine crest
Y
Y
Y
Y
Ball State Univ.
Y
Delaware
Till plain
Y
Y
Y
Y
Griffy Woods
Y
Monroe
Unglaciated highland
Y
Y
Y
Y
School Branch East
Y
Hendricks
Till Plain
Y
Y
Y
Y
School Branch West
Y
Hendricks
Till Plain
Y
Y
Y
Y
Marian Univ.
Y
Marion
Outwash terrace
Y
Y
Y
Y
Lake Station
NA
Lake
Wetland near L. Michigan
Y
Y
Y
Ohio River
NA
Warrick
Reclaimed mine land
Y
Y
Y
Summit Lake
NA
Henry
Till plain
Y
Y
Y
EcoLab
Y
Table 1. Site locations geologic setting and water-balance parameters measured and calculated
References
Allen, R.G., Pereira, L.S., Raes, D., and Smith, M., 1998, Crop evapotranspiration—guidelines for computing crop water requirements: Food and Agriculture Organization of the United Nations:
Irrigation and Drainage Paper 56, Available online: http://www.fao.org/docrep/X0490E/x0490e00.htm, date accessed, January 24, 2012.
Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Englewood Cliffs, NJ, Prentice Hall, 604 p.
Winter, T.C., Harvey, J.W., Franke, O.L., and Alley, W.M., 1998, Ground water and surface water a single resource: U.S. Geological Survey Circular 1139, 77 p.
U.S. Geological Survey, 2012, definition of "streamgage": http://water.usgs.gov/nsip/definition9.html, date accessed, November 7, 2012.
Related sites
Real-time streamgage data for Indiana (USGS)
Real-time groundwater data (USGS)
U.S. drought monitor
NOAA National Climatic Data Center
For more information contact Shawn Naylor ([email protected])