Citizens Energy Group Explains Levee Floodgate Concerns


Susan Brooks, through Karen Glaser, Deputy Chief of Staff, helped us obtain from Citizens Energy Group clarification of their concerns regarding flood gates that would cross the canal. I’ve pasted the information below:

Citizens Energy Group (CEG) strongly supports the city’s efforts on the North Flood Damage Reduction Project and the opportunity it is providing to examine the option of protecting the CEG central canal. The U.S. Army Corp of Engineers (USACE) has stated they do not have a well-developed approach on how to address CEG’s water supply canal, as it is a very unique infrastructure element. As such, the USACE appears to have made assumptions of no impact, which do not match the real technical and operational concerns of CEG, as the owner and operator of the canal. The following are summary points of how the flood gate would impact the canal’s water supply and fire protection of up to 60% of the Citizens Water service area.

1) The operation of a floodgate across the canal causes several operational issues which lead to the disruption of source water to the largest CEG water treatment plant, the White River Treatment Plant (WRTP) which produces 68 million gallons (MG) of the 130 MG of the average daily production. It also places the canal at additional risk to damage from the flooding event over existing conditions.

2) The water supply to the WRTP is by gravity flow which is controlled by the Broad Ripple gate 6.5 miles upstream of the WRTP. The water takes about 9 hours to reach the WRTP. Placing the proposed flood control gate 2.75 miles downstream from the Broad Ripple gate requires the Broad Ripple gate to be operated as a flood control gate as well to avoid overflowing the canal banks within the floodwall line of protection. It would be four (4) hours after the closure of the Broad Ripple Gate before the flood wall gate could be closed. In practice the actual time would be greater because the decision would have to be based on river elevation predictions, and the time to physically close the gates. This delay guarantees a flow disruption to the plant when the gate is closed.

3) The Corps asserts during a flood event the canal will receive floodwater to replace the loss of normal flow. The WRTP would be completely out of source water 3 to 5 hours after the flood gate is closed. The timescale of predicting when the canal would be overtopped would be within 12 hours; much longer than what it takes to affect the WRTP. So even if the canal is overtopped there is still a time period before the flood event where the WRTP would not be producing water. If the canal is not overtopped during an event then the time period the WRTP is out of water would be the entire time the gate is down plus the time it would take to refill the canal after the gate is opened.

4) In the condition when the canal is overtopped it would resupply the plant with floodwater for a period of time. This water presents a set of concerns from a public health standpoint due to potential contamination but it could be used in fire protection.

5) The overtopping event with lowered water levels in the canal will result in more damage to the bank than existing conditions would. Erosion typically occurs down to the water line of the receiving body if not lower until the water surface equalizes on each side of the obstruction. For the canal this equalization will take hours to develop because of the canals capacity to convey water away.

6) When the canal is overtopped CEG will be faced with a choice to risk further damage by keeping water flowing to the canal once the Corps would re-open the gate or to wait until the bank is inspected for damage. Due to the expected additional damage caused by the lowered water level CEG will have to make the safe assumption and disrupt the water flow until damage can be assessed.

In summary operating a flood control gate structure in the canal will result in a disruption to the water supply to the WRTP simply because of the time involved in stopping and restarting the flow to the WRTP. The overtopping of the canal is made worse by the gate structure because of the decrease in water depth prior to the overtopping of the canal. It is expected the canal bank will be eroded to such an extent it will no longer be able to convey water after the flood is over resulting in a loss of water service. CEG would then have to go in and reconstruct the areas damaged by the flooding before water service could be restored. The time of repair would be significant; it would be measured in weeks of outage.

Jim Polito


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