City and county officials study development standards to minimize potential flooding

As the Tomball and Magnolia areas continue to experience population growth, city officials are staying mindful of how flood prevention should play into the way these areas are developed.

Tomball is preparing to adopt its Drainage Master Plan, which seeks to minimize flooding in flood-prone areas. Meanwhile, Montgomery County already places restrictions on developments within floodways, and the city and county work together to keep drainage systems running.

Though cities like Tomball and Magnolia are at higher elevations than the majority of the Greater Houston area, flooding is still the most frequent type of natural disaster for residents, according to the Federal Emergency Management Agency. The significant flooding that took place in July shows the potential impact floods can have on residential areas. Rainwater left parked vehicles around parts of South Cherry Street in Tomball submerged, and high waters forced the City of Magnolia to shut down parts of Nichols Sawmill and Walnut Creek roads.

The risk of flooding can go up as an area becomes more developed, said Mike Talbott director of the Harris County Flood Control District.

"The effects of land development have the potential to increase storm water runoff volume and reduce the time it takes runoff to flow from a site," he said.

Impact of development

The main difference between a rural and a suburban or urban landscape is how much water gets absorbed into the ground, said Kevin Shanley, chairman of the board of the Bayou Preservation Association in Houston.

"The natural landscape stores water," he said. "When we build cities—shopping centers, parking lots—and it rains on that landscape, the water concentrates and runs off at a much higher rate and greater volume. It can all happen in minutes, compared to the natural way where it takes days to run off."

Excess rain can lead to flooding in two distinct ways, Talbott said. The first involves roads flooding because the drainage system is overwhelmed by runoff water. The second involves entire creeks or drainage channels overflowing their banks.

The July floods were notable, Talbott said, for causing Spring Creek and Willow Creek to overflow by significant margins. He classifies the July incident as one of five major flooding events to have occurred in the Tomball area over the past 20 years.

"In general, house flooding has been kept to a minimum [in these areas] because their rural nature typically results in less structural flooding," he said.

Moving forward, the HCFCD is working on various channel improvement projects around Spring and Willow creeks. Two upcoming projects involve clearing brush, garbage and other debris impeding the flow of storm water around three Willow Creek tributaries and repairing erosion along Boggs Gully, a Spring Creek tributary.

Tomball drainage plan

Tomball will move forward in its flood prevention efforts with the adoption of its Drainage Master Plan. The plan, which identifies the city's most flood-prone areas and looks at the best ways to develop them, will likely be adopted by Council in early 2013, said city engineer Lori Lakatos. Tomball also revised a major flood prevention drainage ordinance in 2011, setting standards for developments within flood zones to make sure flood issues do not worsen.

Construction on the M121 drainage channel in Tomball is set to begin in 2013. The channel, which will run along Cherry Street, will provide an avenue for water to drain from the downtown area into a detention pond. The city has plans for additional drainage projects, but lack of funding poses a challenge, Lakatos said. The M121 channel was budgeted at $10.8 million.

Magnolia flooding

Roads in Montgomery County are designed to accommodate a 10-year storm event, said Craig Doyal, Precinct 2 county commissioner. A 10-year storm has a one in ten chance to occur any given year.

Unlike Harris County, Montgomery County does not have a flood control district. As a result, the county is limited in where it can function, Doyal said.

"We can only do maintenance work in our existing rights-of-way," he said. "We can't, for instance, clean a creek channel out if it's outside of our system. We don't have the authority or the funding."

Flooding emergencies in the area are fairly rare, Doyal said.

"We keep ditches open and keep drainage running," he said. "Generally flood waters in our area recede pretty quickly."