Editor’s note: This article is the latest in a series of articles discussing water consumption and use from a supply perspective and as it relates to watershed management concepts. This series will be produced in connection with the Nebraska Water Balance Alliance (NEWBA) and several of its associates.

The word "watershed," depending on its use, conjures up different meanings for different people. Dictionary.com defines a watershed in several ways. One is the region or drainage area drained by a river or stream. In Europe, the term is more commonly used to describe the dividing line between neighboring drainage basins. For some, it's a turning point or divide that affects opinions or actions — a "watershed moment."

For our purposes, however, a watershed is defined by the U.S. Geological Survey as an area of land that drains all streams and rainfall to a common outlet — like the outflow of a reservoir, mouth of a bay, or any point along a stream channel. It's a closed system that allows it to be assessed and managed in a watershed-wide approach. A watershed can be anything from the Mississippi River Basin all the way down to a small farm or stock pond. Even a relatively small, isolated aquifer could be managed as a watershed if its recharge comes from a defined area and it has at least one well depleting it.

Big vs. small
And when it comes to watershed management, scale matters. What makes sense at a smaller scale may be completely ineffective or inappropriate at a large scale. "At bigger scales, management can gain understandings and set goals or expected outcomes. At smaller scales, management can implement individualized and focused applications to address local needs," explains Frank Kwapnioski of H2Options Engineering LLC of Lincoln and NEWBA adviser. "However, aggregations of these local efforts can and do have impacts at the larger, aquifer, streamflow, or even river basin scale as well."

SCALE MATTERS: The HUC system used by USGS is an already defined mechanism that can be used to address different levels of scale. This map shows part of the Platte River Basin, categorized as a HUC4 by USGS, and which is made up multiple HUC8s, HUC10s and HUC12s — one of which is highlighted in green. (Map courtesy of USGS)

For example, a least-common denominator type approach can be suited to watersheds at a large scale — like the entire state of Nebraska or the Platte River Basin. This might mean a general approach like determining the water budget for the entire area and deciding that in order to remain sustainable, all consumptions should not exceed the total supply over the long term. This type of least-common-denominator approach at a state scale could be based on long-term average annual precipitation, consumption and use of the different land practices in the state, as well as any downstream outflow requirements.

Related: A watershed-wide approach to managing water supply and Understanding water consumption: Where does it all go?

At the farm scale, or smaller river basin level, a similar but more site-specific approach could be considered. Trying to balance a water budget based on consumption at the land surface might not make sense for a small aquifer in eastern Nebraska, but it may make sense where large aquifer systems, like the Ogallala, could be practically used as renewable reservoirs to help allow for climatic variability across the remainder of the state.

System handles different levels of scale
The Hydrologic Unit Code (HUC) used by the U.S. Geologic Survey is an already defined mechanism that can be used to address different levels of scale.

For example, the Mississippi River Basin is made up of a number of HUC2s, which need only two digits to identify them. Smaller watersheds, like the Republican River, are HUC4s, and are made up of multiple HUC8s and HUC10s. Finally, at the smallest classification, are HUC12's. Smaller yet is the individual farm. As the scale gets smaller, assessments can be refined to a more precise degree, and that could include the relationship between surface and groundwater constraints.

"It goes all the way down to the individual farmer looking at things circle by circle," says Jim Goeke, emeritus research hydrogeologist at the Conservation and Survey Division in the School of Natural Resources at the University of Nebraska-Lincoln. "If sustainability of water is our goal at the state level, what steps do we need to take at the individual level, the NRD [Natural Resources District] level and state level to accomplish that?"

ZOOMED IN: This map shows the HUC12 highlighted in the previous map, but zoomed in to give a closer look at the HUC12 scale. Managing a HUC12 watershed takes a more precise level of management compared to a HUC8 or 4. (Map courtesy of USGS)

"When you manage a watershed, you start by measuring how much water is coming in from a certain source — in most cases, precipitation. What happens to it? Evapotranspiration is a major component. When you look at individual farm units to see how much is lost to evapotranspiration, you measure how much water is being consumed," says Ted Tietjen, NEWBA project coordinator. "Once you get that data, if you're using more than what the demand is, more than what's available, then you've got to figure out what to do to get there."

The first step at the farm level is understanding consumption, says Roric Paulman, NEWBA board chairman who farms near Sutherland. "You would have potential to talk about how much consumption you can have on your farm. You would have values for different crops and what those values mean. That determines if you plant a different crop or retire a certain number of acres or a combination of practices," Paulman says. "Could you take a risk and pray it rains more, or integrate practices that reduce consumption on your farm? It sets in motion a whole different level of thinking."

If systematically considered at the proper scale, many water management concerns can be addressed with concepts as simple as checkbook math.

In upcoming articles, read about strategies for measuring and managing water consumption and use at the farm level that can help achieve the overall goals for a balanced water budget at the appropriate scale.