SCOPE OF WORK
The City of Bellaire, Texas (the City) has experienced flooding conditions over the years that have recently become more and more frequent. On many occasions, there has been structural damage to residential property, commercial property and public facilities. This damage has been costly to the citizens of Bellaire and at times, interrupted the City’s ability to provide health, safety and welfare services to the residents. In the city limits of Bellaire alone, over 1400 homes flooded during Tropical Storm Allison and over 2000 homes flooded during Hurricane Harvey. Also, many structures flooded during much less severe rain events: the May 2015 storm and the Tax Day storm of 2016.
The scope of services for this project includes the development of a Master Drainage Concept Plan (MDCP) for the City of Bellaire and portions of the City of Houston. The plan will determine feasible improvements to reduce flooding potential within the City of Bellaire and surrounding areas. The City of Bellaire is generally encompassed by Harris County Flood Control District’s (HCFCD’s) Brays Bayou Subarea D115A, which is approximately 2,400 acres. The drainage systems within D115A extend from US 59 South to the outfall into either Brays Bayou or Cypress Ditch, mostly via underground storm sewers within the major thoroughfares, as shown on Exhibit 1. The local drainage areas include storm drainage from the City, City of Houston (COH), TxDOT and HCFCD right-of-way (ROW). The area has a history of drainage issues due to the lack of storm sewer capacity and the widespread Brays Bayou floodplain. Also, there appear to be large drainage areas, outside the D115A local North/South drainage system drainage areas, that contribute overland sheet flow into the individual drainage area systems which overwhelms the local systems.
The City, TxDOT and HCFCD have agreed to an interlocal agreement to analyze the capacity of the existing major drainage systems which serve the City and determine recommended improvements to these systems to prevent structural flooding in storm events, up to and including the 100-year, 24-hour storm event.
This analysis will simulate the existing drainage conditions of the major drainage systems that impact the City and nearby COH: Brays Bayou, Cypress Ditch, Kilmarnock Ditch, Newcastle Storm Sewer, IH 610 storm sewer system, the South Rice Avenue storm sewer system, and the Chimney Rock storm sewer system. Pertinent lateral storm sewer systems, which outfall into the main trunk systems, will be evaluated, as necessary, to identify major overland sheet flow patterns. Additionally, areas outside of the normal delineated drainage area boundaries will be evaluated to determine potential sheet flow impacts within the city limits. These analyses will include possible overflow from the Buffalo Bayou watershed in the vicinity of Westpark Drive.
The result of the study will be a comprehensive drainage plan that the City, HCFCD, TxDOT, and the COH can use to improve the major North/South drainage arterials. The improvements proposed will provide storm drainage relief to the watershed. The results will include the benefits and costs of all drainage solutions presented and a recommended plan for implementation.
The plan will include an evaluation of the existing storm drainage network and evaluate conceptual improvement recommendations to improve the system. Each system’s level of service capacity (2-, 5-, 10-, 25-, 50-, 100-, 250- and 500-year, 24-hour storm events) will be determined and proposed improvement scenarios will be developed to lower peak water surface elevations and protect structures within the city. Detention basin locations will be determined to reduce impacts from proposed improvements so as to eliminate any impact on flooding conditions along Cypress Ditch, Brays Bayou, and surrounding properties.
Bellaire has flooded from various severe storms over the last century. While the City of Bellaire is dedicated to minimizing adverse impacts associated with flood events, several factors contribute to flooding in Bellaire that are not under the City’s control. Some of these are:
very high average annual rainfall of about 50 inches
very flat topography
clay soils that do not absorb water very well
close proximity to an undersized Brays Bayou
large amounts of storm water from the City of Houston flow into Bellaire from the north
localized storm water runoff from Bellaire drains into undersized drainage systems owned by the City of Houston
The City of Bellaire does control the drainage improvements constructed within the City limits and the finished floor elevation requirements for new residential and commercial development.