Discrepancies Between HUC Boundaries and Karst Basin Boundaries By James C. Currens Kentucky Geological Survey in cooperation with Joseph A. Ray Groundwater Branch, Division of Water October 18, 2001

Federal Standards for Delineation of Hydrologic Unit Boundaries Revised June 12, “The criteria and methods for hydrologic unit selection and boundary delineation will permit standardized hydrologic units to be used by a diverse group of users serving multi-agency programs. Some examples of these programs include watershed management, water quality initiatives, watershed modeling, resource inventory and assessment, and establishing total maximum daily loads. The utility of hydrologic units of various size and complexity based primarily on natural surface water flow and topographic landforms cannot be underestimated for the potential invaluable analytical and statistical purposes and applications at hydrological and ecosystem scales.”

Hydrologic Unit Definition Revised June 12, “A hydrologic unit is a drainage area delineated to nest in a multi-level, hierarchical drainage system. Its’ boundaries are defined by hydrographic and topographic criteria that delineate an area of land upstream from a specific point on a river, stream or similar surface waters. A hydrologic unit can accept surface water directly from upstream drainage areas, and indirectly from associated surface areas such as remnant, non-contributing and diversions to form a drainage area with single or multiple outlet points. Hydrologic units are only synonymous with classic watersheds when their boundaries include all the source area contributing surface water to a single defined outlet point.”

Characteristics of Karst Basins after Steve Worthington, Ph.D., 2001 Tributary flow to springs. Turbulent flow in conduits. Conduits occupy troughs in the potentiometric surface. Hydraulic gradient decreases downgradient. Hydraulic conductivity increases downgradient. K from numerical models is much larger than the geometric mean K from aquifer tests.

Water Budget Water budgets calculated using annual statistics indicate yield from karst basins in the Mammoth Cave area is 14 to 19 percent more than runoff from similar sized, non- karstic, bedrock basins in the same region. (Hess, 1974, Hess and White, 1974) Therefore, per unit area, the water contribution to surface flow from karst basins is more significant than that from non-karst basins.

Areas of Shallow Soluble Bedrock in the Conterminous States 20 percent of the area of the 48 states is underlain by karst.

Hydrologic Units of the Big Spring Basin, Missouri

Tracer Flow Routes in the Barton Springs Basin, Edwards Aquifer, Texas Courtesy of Nico M. Hauwert, Hydrogeologist Watershed Protection and Development Review Department City of Austin

Southwest Fillmore County, Minnesota Watershed Boundaries (PINK and BLUE) Courtesy of Jeff Green, Minnesota Department of Natural Resources

Tufa Falls Karst Basin Sequoia and Kings Canyon National Parks, California Courtesy Joel Despain, NPS Cartography by Shane Fryer Green: watershed boundary Red: karst basin boundary

Additional Examples West Virginia - All flow of upstream Culverson Creek in Greenbriar County sinks and discharges from springs along Silver Creek, across several drainage divides. West Virginia - Simmons Mingo Cave in Randolph County pirates flow form the Tygart Valley ( ) to the Elk River ( ). Indiana - Indian Creek, a tributary to the Ohio River, sinks entirely and emerges at Harrison Spring on the Blue River.

Karst in Kentucky: Fifty-five percent of the state has potential for karst. Areas shown in red have high potential for karst Areas shown in green have moderate potential for karst Areas shown in blue have limited potential for karst

Turnhole Spring Basin, Mammoth Cave Karst Green River Hydrologic Unit Barren River Hydrologic Unit km 2 (85 mi 2 ) HUC Boundary

Basins in the Western Pennyroyal, Kentucky Hydrologic Unit Boundaries (blue) Karst basin boundaries (green) HUC boundaries make significant excursions from karst basin boundaries.

Basins in the Inner Bluegrass, Kentucky Hydrologic unit boundaries (blue) Karst basin boundaries (green)

Storm Response of Karst Springs

Stage-Discharge Rating Curve for Pleasant Grove Spring, Illustrating Range of Discharge

Summary Approximately 20 percent of the area of the conterminous United States is potentially affected. Karst basins respond rapidly to precipitation, in a manner similar to surface streams. Karst springs provide significant percentages of flow to streams. Karst basin boundaries frequently do not coincide with hydrologic unit boundaries. These discrepancies are commonly significant.

Recommendations Assign karst basins or “noncontributing areas” to watersheds according to dye tracing results. In karst areas where karst basins have not been mapped, hydrologic units should be indicated by a special pattern, or attribute, keyed to a disclaimer. The involved federal agencies should support future karst basin mapping by state agencies.

HUC delineation should be both accurate and precise In karst areas, twelve digit and smaller hydrologic units can only meet the programs stated hydrologic uses if the discrepancies with karst basin boundaries are reconciled.