Further IFIM Study Information

Our consultant’s staff is on the river collecting the required data for the IFIM study at the ten (10) transect locations. Originally we planned to get the 50 cfs stage done this week. After Hurricane Irene and tropical Storm Lee left their mark on the watershed the consultant was unsure of what the river conditions would be at 300 cfs so they planned on getting the second stage, 150 cfs, done as soon as river flows dropped to that flow. It would not be possible to control the amount of water released for the study if the natural flow was greater than the targeted flow of 150 cfs or there wasn't  sufficient storage volume below the spillway to hold the inflow that exceeded 150 cfs.

After working on the river setting up the transects the consultant concluded they could work safely at 300 cfs and suggested proceeding with that stage while river flows are still elevated rather than wasting the time, and the water, waiting another day or two for flows to drop to around 150 cfs. If it took more than 1 day for the flows to reach 150 cfs the schedule would have to slip to next week for the first stage of the field work. After estimating what the inflow would probably be based on yesterdays flows upstream I concurred with their suggestion and proceeded with the 300 cfs flow stage.

Today’s estimated inflow, based on the flow past the Deep Creek and Mattoax gauges yesterday, is 256 cfs using the new formula and 324 cfs using the old formula. If we release 300 cfs downstream and withdraw approximately 50 cfs for water supply, we would take out/release about 100 cfs more than the lower estimated inflow. One hundred (100) cfs equals 65 million gallons or slightly less than a one inch (1”) change in the reservoir level when it is nearly full. Given that inflow will decrease over the 2-3 days of data collection the reservoir level should not drop more than 6 inches, including evaporation,  during this period. The remaining controlled release rates, 150 cfs and 50 cfs, should be less than the daily inflow and the reservoir should recover some, if not all, of the storage volume released during the 300 cfs stage of this study, even if we do not receive any of the rain forecast for tomorrow and Friday.

Update on the IFIM Study

The sub-consultant performing the field work for the above study started setting up the study locations along the river today. Originally the plan was to run the lowest flow study at these locations this week but the lingering effects of Hurricane Irene and Tropical Storm Lee have kept the river flows too high to run that stage at 50 cubic feet per second (cfs) or about 32 million gallons per day (mgd). The plan this morning was to set everything up and get started late today or first thing tomorrow morning after the flow was down to the second stage of 150 cfs or 97 mgd. After working in flows near 300 cfs all morning the consultant recommended taking advantage of the current elevated flows and run the highest stage which is 300 cfs or 194 mgd.

There was still a small amount of water coming over the spillway with the hydro-electric facility discharging 250 cfs through their facility so we concurred with the consultant’s recommendation. We have asked the operator of the hydro-electric facility to go back to discharging 300 cfs until Thursday afternoon when this stage of the study will be complete.

This release will draw the reservoir down more than if we only released the required amount under either our Virginia Water Protection permit or our agreement with the City of Hopewell. When this first stage of the study is complete on Thursday we will resume releasing the required amount. We anticipate the inflow will be sufficient to hold the reservoir level at that time steady or to cause it to rise slightly due to the still elevated inflow and more seasonal water demands.

If you have any questions about this study please contact me at (804) 590-1145 or by e-mail at dawson@arwava.org.