Water Management Situation Report for Cumberland River Basin Reservoir System and Associated Waterways

Wolf Creek/Lake Cumberland - Fall 2009

Severe drought conditions in 2007 and 2008 required adaptive water management at Wolf Creek Dam and Lake Cumberland.  During 2009, a new set of challenges arose as it was a wet year for a change!  The arrival of more regular and plentiful rains beginning in November 2008 and continuing to the present has created new concerns about water quality in the lake.  Concerns about depleting the quantity of water available for the Cumberland River system downstream from Wolf Creek Dam decreased slightly as it looked like supply for downstream needs for the growing season would be adequate.  Indeed, this was what happened from summer and into early fall.

The winter of 2008-2009 was fairly, consistently cold and was followed by a relatively cool spring and cloudy, mild summer.  Normally these conditions would yield abundant, cold, well oxygenated water downstream.  However, the abundant precipitation and runoff of the spring resulted in significant pool rises for Lake Cumberland, peaking with a major rise in early May to around elevation 695, or nearly 15 feet higher than the desired 680 elevation at Wolf Creek Dam.  The 680 pool elevation guidance is based on concerns about dam safety as repair and rehabilitation for seepage continues.

What followed this rise was the need to evacuate huge quantities of water quickly.  Unfortunately, what went out of the reservoir was all that nice, cold, well oxygenated water.  This was replaced by warmer, silt carrying, and oxygen demanding water.  In addition, even as that big May rise was finally drained away and lake levels again approached elevation 680, more summer rain events led to additional smaller rises.  This meant remaining cold water was lost, so by late September and early October 2009 no reserves of really cold water remained in the lake.  The effect of this was that water temperatures deep in the lake at the penstock level (60 feet in depth) and sluice level (110 feet in depth) were anywhere from 8 to 10 degrees Celsius higher than the same time in 2008.  It was no surprise that dissolved oxygen conditions also deteriorated more rapidly in the lake this year during late summer and fall compared to the two previous drought years. By early September, oxygen in the cooler waters below the thermocline had sunk to lethal levels and there was virtually no oxygen in water cooler than 77 degrees.  These conditions forced striped bass and walleye into the warmer, shallower water above the thermocline.  Although striped bass were likely stressed during August and September, no major striper kills occurred.  However, a walleye fish kill occurred near Wolf Creek Dam on September 13th.  The Kentucky Department of Fish & Wildlife Resources (KDFWR) and Corps of Engineers (Corps) personnel investigated the kill on September 14th and observed about 175 dead walleye from 2-5 pounds.  Apparently, these walleye succumbed to the low oxygen levels in the cooler waters and didn’t move above the thermocline until it was too late.  Fortunately, the fish kill was restricted to a small area near the dam and no other fish kills were observed.

These conditions reduced the volume of suitable habitat for coolwater species such as striped bass and walleye.  Sluices were used at Wolf Creek Dam for two purposes, both to assist with pool level control and later in the summer to mix well aerated waters with the turbine flows.  The heavy use of sluices along with generally cooler weather during the fall did have the positive effect of more quickly destratifying the lake, so that by October 28th it was possible resume turbine only discharges.  Normally the lake does not destratify until sometime in December. 

Winter will bring cooler weather and more favorable conditions for these fish.  As the lake cools, the thermocline will break down and the lake will eventually “turnover”.  This will reoxygenate the lake at all elevations.  Water quality in the lake should remain good through the winter and early spring.

Wolf Creek/Lake Cumberland - Spring 2009

As fall ended and early winter 2008 began, Lake Cumberland continued to destratify. While this seasonal pattern was happening, regular rain producing systems began to move through the Cumberland River Basin, a welcome event. Complete destratification of the lake occurred by middle to late December 2008. This allowed the orifice gates to be closed by the U.S. Army Corps of Engineers (the Corps). Winter 2008-2009 was colder than recent winters and had several sustained periods of extreme cold for this part of the country. The cold combined with gradual recharging of ground water from rain systems helped the water management outlook in the Cumberland Basin because it resulted in a colder, more oxygenated reservoir with the promise of better sustained streamflow from groundwater sources for the coming season.

Sometimes however, there can be too much of a good thing. In April and May 2009 numerous, heavy rain producing systems led to the sudden rise of reservoirs throughout the Cumberland River Basin. Lake Cumberland rose dramatically in early May. The spring rise caused by massive warm water inflows may have the effect of flushing out or diluting the cold, well oxygenated water in the reservoir. Also, along with the water comes nutrients and other oxygen demanding materials that, as they decay will consume vital dissolved oxygen (DO) at a rapid pace which may hurt lake ecology and fish species such as walleye and stripers. It is too early to tell at this point, but most signs indicate the possibility of more problems related to low DO in the lake than has been seen for several years.

As summer progresses, the lake will stratify into temperature layers and the coolwater fisheries (striped bass, walleye, and smallmouth bass) will seek out the cooler depths of the thermocline. D.O. levels in cooler water may decline to critical levels by early fall and we could experience a fish kill of larger striped bass and walleye. Oxygen levels typically are lowest in late September and October, before the lake turns over.