KERR LAKE MANAGER GIVES CORPS ANSWERS TO LOW WATER LEVEL QUESTIONS RECENTLY RAISED BY READERS
The following is an answer in response to several readers questions on following the guide curve that actually mandates, along with weather, the water levels or lack thereof of Kerr Lake. KLPW, asked several times to review the procedures, posted comments and questions by Kerr lake user, Jim Arnold. Below is the response to Mr. Arnold’s comments and questions by Resource Manager Michael Womack.
As you point out, Kerr Lake is a multi-purpose reservoir. As such, our target lake level varies seasonally to better accommodate different purposes–flood storage year-round, but especially in the winter; spawning releases in the spring; and recreation in the summer. Hydropower is a primary purpose of the project year-round and provides affordable power to a number of communities and electric cooperatives across Virginia and North Carolina.
Wilmington District water managers make every effort to maintain lake levels at or near these seasonal target lake levels (also called our guide curve); however, actual rainfall (surplus or lack of) determines how well those target lake levels can be maintained. Where the lake level is relative to the guide curve determines how we operate the project. Generally speaking, if the lake level is above guide curve, we make controlled flood releases to bring the lake back down near guide curve to restore our flood storage. If we are below guide curve, as we have been all summer due to below-normal inflows into the lake, we conserve water by reducing our energy generation to the minimum amount that we are contractually obligated to generate. These minimum energy requirements also meet the minimum flow requirements to maintain downstream water quality. Our minimum energy commitments are highest in the summer and winter months when power customer demands are the greatest; however, these minimum energy amounts decrease significantly (by 33%) in October, which will allow us to conserve even more water and hopefully allow lake levels to begin to recover.
While there has seemingly been decent rainfall at Kerr Dam this summer, keeping the lake full depends on widespread rainfall across the entire Roanoke River basin upstream of Kerr to sustain inflows–but this has not been the case this year. Since April, inflows into Kerr have only been averaging about 50% of normal (based on long-term monthly median inflows), and since the beginning of July, averaging only about 40% of normal. As a result, lake levels have been steadily dropping despite only generating our minimum energy amounts since the beginning of July. Without significant late summer rainfall, often associated with tropical systems, protracted lake level declines can result in recreation impacts, as is currently the case.
The following link takes you to our Project Status webpage, which you may already be familiar with (http://epec.saw.usace.army.mil/jhk_summ.htm) and shows lake level plots for the past 2 years (along with the drought curves you mention) and also monthly average inflows for the past 2 years. The Drought Alert curve is a relative indicator of drier-than-normal conditions, but doesn’t trigger any specific response other than just increased awareness. While there hasn’t been an official drought designation in the NC and Virginia portions of the Roanoke Basin this summer, the National Drought Monitor has persistently designated this area as “D0” this summer, which indicates “abnormally dry” conditions.
The Monthly Average Inflows plot on our webpage reflects the below-normal (below-median) inflows mentioned previously. Comparing last year to this year, inflows and lake levels trended similarly, but with a couple of exceptions. First, higher inflows last spring (2011) allowed the lake to stay above guide curve a few weeks longer and track about a foot higher through most of the summer. Second, above-normal inflows last September following an extremely dry August (2011) allowed lake levels to recover slightly and stabilize around elev 296 and not continue to decline as we have seen this year. Of the months you mentioned (July, Aug, Sep), our records indicate that only Aug inflows were higher than last year’s, but were still only about 50% of normal and didn’t allow for any significant improvement.
Michael T. Womack
Operations Project Manager
John H. Kerr Reservoir
KLPW is always interested in comments or questions regarding the public use areas and public use of the John H Kerr Reservoir. Use the post capabilities here or send us an email to firstname.lastname@example.org.