With an estimated 20 trillion gallons of water dumped on Houston via Hurricane Harvey in a very short amount of time, Houston has few options when it comes time to drain their current excess of water.
Because Houston sits on a low-level coastal plain, it is very flat, which is bad for draining water. If Houston had any form of a slope, the water would drain much faster and easier.
Because Houston has grown so rapidly in the past handful of years, buildings and highways, which are made primarily of cement, now exist where wetlands once were able to soak up water overflow. The infrastructure to handle the aftermath of these storms was overlooked by the development of Houston. Houston is simply more susceptible to flooding, because of the city’s proximity to the coast. Many houses and buildings have been built on land that is prone to flooding.
Houston’s annual rainfall is somewhere around 40 inches per year. However, most of the areas in and around the city received that amount of rainfall within the first hours of Hurricane Harvey’s downfall. Receiving a year’s worth of rainfall in a very short amount of time would be difficult for any area to handle, but especially an area such as Houston that is not built to sustain extremely heavy rainfall.
Instead of Houston having some high-tech solution to combat this problem, the city will merely have to wait for the water to dissipate on its own. Unlike New Orleans, Louisiana, the city of Houston does not have any pumps, levees, or floodwalls to release the water. Houston is, instead, left to rely solely on its few bayous to serve as the city’s drainage system. A bayou is simply a slow-moving, meandering stream or creek. Houston has 10 bayous, which flows west to east, then into the Houston Ship Channel, and finally into Galveston Bay in the Gulf of Mexico.
However, most of the bayous have already been filled with too much water. These bayous were not built to support, let alone transport, nearly this much water. Most bayous hit their capacity of water during a 1-in-25 storm. In stark contrast, experts agree that Harvey has produced a 1-in-500 storm. Therefore, Houston is out literally out of its depth with no alternative but to wait for the water to subside on its own.
A few decades ago, the city of Houston built two flood control reservoirs in order to protect the downtown area. Both the Addicks Reservoir and the Barker Reservoir have earthen mound dams, along with gates that are able to open and close with the goal of capturing water that would otherwise flow into the city.
After the storm has passed, the Army Corps of Engineers, which operates the reservoirs, opened the reservoir to release a controlled amount of water into the Buffalo Bayou, which runs through the city. This process was repeated until the reservoir was drained.
However, Addicks repeatedly overflowed, causing water to spill over the reservoir. Barker is expected to follow the same pattern. The day after the Army Corps of Engineers released controlled amounts of water from both reservoirs, with the goals of relieving pressure on the dams and preventing stormwater from uncontrollably being released from either reservoir, a levee at Columbia Lakes in Brazoria County, located outside of Houston, was breached with floodwater.
Nobody, expert or private citizen, is able to give a definitive answer as to how long it will take for the bayous to drain the trillions of gallons of water from the city. The amount of time that it takes will also depend on the particular location in the city. While some parts of the city are expected to drain its water in a matter of hours, other areas might not be dry again for a matter of days, maybe even weeks. It mostly depends on how much rain fell in a particular area.
While experts agree that Houston will require a better drainage system in the future, these same individuals differ on whether or not a pumping system would be the best solution. Regardless, it is widely agreed that building higher elevated buildings and houses above the floodplains, as well as expanding the reservoirs, relocating houses away from the bayous, restoring natural water absorbing surfaces, protecting existing natural water absorbing surfaces, such as wetlands, and many other preventative measures are necessary steps to take.