- Heavy rains and in-flowing stormwater cause pool levels in the Addicks and
- Barker reservoirs to reach a certain level, and
Controlled releases from the reservoir outlets into Buffalo Bayou are unable to compensate for this increase
THEN uncontrolled stormwater can spill over the concrete-armored spillways at the ENDS of the two dams into areas outside the reservoirs. (see map above)
This type of uncontrolled release has been relatively minor during Harvey. Rising stormwater in the Addicks Reservoir began spilling around the north end of the Addicks dam August 28, near the intersection of North Eldridge Parkway and Tanner Road. Uncontrolled releases are NOT EXPECTED around the south end of the Addicks dam, and are NO LONGER EXPECTED around the Barker Reservoir dam.
While the Corps’ design of the reservoirs anticipated this type of event, it is the first time this has happened in the 70-plus-year history of the dams. It is also the first time that homes upstream of the reservoirs have flooded from rising water in the reservoirs.
The stormwater spilling around the ends of Addicks Reservoir first impacted the Twin Lakes on Eldridge and Lakes on Eldridge subdivisions, which are also located near the intersection of North Eldridge Parkway and Tanner Road on the north side of the Addicks Reservoir. Other areas along the east side of the Addicks Reservoir will also see additional stormwater.
Addicks and Barker reservoirs were built in the 1940s to prevent flooding of downtown Houston and the Houston Ship Channel. The Corps is continuously monitoring the structural integrity of the dams, including the ends of the dams. This work includes balancing the flow of stormwater into the reservoirs with releases through the reservoir outlets. This effort must take into account Hurricane Harvey's historic rains, the resulting high water levels in both the reservoirs and along Buffalo Bayou -- all of which can cause flooding -- and the need to build capacity in the reservoirs in case of further rainfall.
- Rising reservoir pools can spread outside of government-owned land into neighborhoods adjacent to the reservoir, causing flooded streets and homes. This is already occurring.
- Higher-than-normal releases from the reservoirs can contribute to flooding on Buffalo Bayou. These “surcharges” are already occurring, as is flooding.
- Uncontrolled stormwater going around the end of the Addicks dam is of concern in connection with protecting structural integrity.
Both ends of each dam include concrete-armored spillways. Stormwater escaping around the ends of the dams is considered preferable to water overtopping the reservoir dam itself. However, controlled flows from reservoir outlets are considered preferable to uncontrolled flows, both for the integrity of the dams and the potential impacts to adjacent neighborhoods and downstream areas along Buffalo Bayou.
Outlet gates at the Addicks and Barker dams are releasing record levels of stormwater that has been stored in the reservoirs in response to Harvey’s historic rainfall in Harris County. These additional releases have resulted in out-of-banks flooding in neighborhoods along Buffalo Bayou, the receiving bayou from the two federal reservoirs.
Addicks and Barker reservoir levels will start to lower slowly with the releases. Creeks and channels that flow into the reservoirs are also ponding water at the same level as the reservoirs, but will start to recede as the reservoirs lower. Adjacent stormwater detention basins will do the same. All levels will decrease as the reservoir levels are reduced.