Council discusses Master Drainage Plan

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Manvel city council again discussed the Master Drainage Plan that was presented initially in early 2014. Klotz Associates was retained by the city at a cost of $50,000 to prepare the Plan with the underlying objective to provide recommendations for drainage improvements to the city in order to meet continued growth and future needs. Authors described the Plan as “providing guidance for council, future developers, future interested parties, engineers, special interest groups, MUD Districts, and others to have a feel for what drainage improvements would be needed to improve and take care of the drainage within the city. As developers come forward will need some kind of direction on how much right-of-way will they need to donate or provide as part of their drainage plan for their development. The Master Plan is simply a guide to work with for future developers.”

Manvel deals with three unique Drainage Districts. Pearland’s Drainage District 4 oversees 27% of the area primarily in the central northern and some of the western portions of Manvel. Brazoria County Drainage District 5 oversees 15% of the area primarily in the southern portion of the city. And the Conservation and Reclamation District 3 oversees 55% of the area primarily in the eastern portion. Three percent of the city has no Drainage District authority at all. Analysis of the area shows that 34% of the city is in a floodplain and 3% is in a floodway based on FEMA criteria. A floodplain is an area near a river, stream, or bayou which floods when the water level reaches flood stage. A floodway consists of the stream channel and adjacent areas that actively carry the flood flows downstream.

Two scenarios were proposed in the Plan. One deals with currently existing flows within the banks of all major channels, and ultimately within the proposed right-of-way. This scenario reflects an option for the city to prepare for and promote future channel improvements primarily by adding sub-regional detention ponds located at areas north of Hwy 6 or by on-site detention. A second scenario reflects an option for the city to prepare for and promote future detention mitigation that would convey the 100-year flows within the banks of all major channels and ultimately within the proposed right-of-way. The scenarios are not easily described in a few sentences as the plans include many considerations. In a few words, scenario one basically entails a combination of strategies that includes individual on-site detention. An example of on-site detention would be a development sharing its property with a dug out pit designed to collect and hold storm water runoff until such time that it can be dispersed downstream with no adverse impact to its neighbors. This scenario would require less land for common drainage flows through bayous, creeks, and reliefs.

The second scenario provides for regional detention ponds that would be accessed from developments. This scenario would allow for a more attractive city in that each development would need not engineer a unique detention pond just to manage its impact. It also would allow developers greater flexibility in what and how they can design. Since the portion of the development that would have been required for detention would no longer be necessary more land would be available for the project. The downside to this scenario is that more community property would be required to house the regional detention ponds and the common drainage flows through bayous, creeks, and reliefs would need to be even larger that the first scenario.

Proposed costs for each scenario approximates more than $125 million in today’s dollars. The bulk of the costs would be borne by future developers though the city will be required to fund some improvements as well. Several funding strategies were proposed including external funding sources, utility or special districts, impact fees, and various types of internal funding mechanisms.

Some on council have taken issues with the Plan and its cost and question the perceived adverse effects on current residents and their property limits. Most outspoken is member Melody Hanson. She expresses concerns that some Manvel residents would likely see the majority of their backyard “wiped out” if the proposed widths of waterways as spelled out in the Plan were implemented. She sees the Plan as radically changing neighborhoods and ecologically compromising large oak trees that rely on water from the natural overflow of swollen waterways. “You could wipe out an entire wooded area,” she said. “If you take out the dynamic of the bayous and the trees here, that is about all we’ve got going for us; they are among the few things we have that make Manvel unique and beautiful. We are taking a natural tributary and we are altering it hugely. I have concerns about that.” She says the Plan as proposed impacts most severely the people downstream that have lived in Manvel the longest as most of their homes were constructed near waterways. Hanson goes on to say that the “thrust of the Plan is wrong.” She says the Plan is for developers and future growth, not for the people who live here now and are burdened by poor drainage. New development should shoulder the burden of the changes growth will bring, she believes. “It seems so imbalanced to me.”

Hanson also is concerned that council’s questions have not been answered by the authors of the Plan. She says the revised Comprehensive Plan the city is adopting has an entire section devoted to drainage concerns and feels it is the number one issue citizens have. She thinks sufficient time needs to be devoted to seriously analyze the Plan and it impact on the community. Authors of the Plan have refused to address council inquiries until an agreement is reached that will pay them an additional nine thousand dollars. Hanson says that is a “lot for two pages of questions. I’m not saying let’s reject it. I’m just not ready to enact it and take the word of one consultant and radically change our city because of it. I see it more as a drainage study versus a drainage plan.” Until the questions council has are answered, Hanson emphasizes an emphatic no to any approval of the Plan as it is currently understood.

The city manager has been directed to further negotiate with the authors of the Plan in an effort to come up with a “more reasonable” price.

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