SECTION I - SUMMARY
The purpose of this phase of the Comprehensive Drainage Plan (CDP) project is to provide the City of Houston with sufficient information on its storm sewer systems so that the City of Houston Department of Public Works and Engineering (City) can identify and plan future capital expenditures. Management of the systems requires a plan that contains information on the location and extent of drainage inadequacies, a criteria on which to base system improvements, the cost to implement the improvements, and a method to prioritize the improvements.
The purpose of this phase of the CDP project is to prepare a Capital Improvement Plan (CIP) for the City to use in planning future capital expenditures to address the needs of its storm sewer systems. The CIP identifies inadequate systems, proposes improvements, presents probable costs associated with the proposed improvements, and assigns a relative priority to each improvement. This is accomplished through the use of the criteria developed as a result of the first phase of the CDP and through the use of a web-based Geographic Information System (GIS) and storm sewer analysis tool (HouStorm) developed in this phase of the CDP.
The web-based GIS summarizes the findings of the engineering effort performed to develop the CIP. These cost data may be increased based upon known cost adjustment factors. These proposed improvements consist of upgrading existing storm sewer systems to meet current City of Houston drainage criteria, and do not include new sewers required to serve undeveloped areas.
Authorization for the City of Houston Comprehensive Drainage Plan is covered in the terms of an Agreement between the City of Houston and J.F. Thompson, Inc. (Thompson), dated April 4, 2001.
The Study Area addressed in the CIP includes drainage systems consisting of existing storm sewers, roadside ditches, and a combination of the two, located within selected areas within the City of Houston corporate limits (City limits). Project information is organized according to Harris County Flood Control District (HCFCD) major channel watershed boundaries and designations. The drainage systems included in the CIP are located in the following watersheds:
Procedures used to develop the CIP are discussed in detail in Methodology Sections II - V. The following is a summary of these procedures and results.
Criteria
To determine whether a storm sewer system required modification or improvement, several factors were considered. The factors include compliance with the City’s storm sewer design and drainage criteria, historical flooding, and land use patterns. The following is a summary of the information considered to determine a system’s selection for improvement.
Geographic Information System
As a tool to display and interact with proposed CIP improvements, an Internet / web-based GIS was developed to reflect existing and proposed storm sewer systems and other drainage-related features. ArcGIS and ArcIMS where used to create this tool. In addition, the GIS was configured for use with a storm sewer analysis program called HouStorm. The data sources used to develop the existing storm sewer systems GIS were the City of Houston Planning Department data (Synercom computer format) and the City’s Geographic Information Management System (GIMS). Storm sewer construction plans obtained from the City File Room supplemented the GIS data.
Part of the GIS coverages (files) used for the development of the CIP were:
The following should be noted concerning the GIS:
HouStorm
To evaluate storm sewer systems using the GIS and to size proposed modifications, a storm sewer analysis program (HouStorm) was used specifically for this project. HouStorm uses the Rational Method to determine peak discharges, and calculates the hydraulic gradient for existing and proposed storm sewer systems. In addition, HouStorm indicates the approximate size a storm sewer system must be to meet current City design criteria. After proposed modifications were determined, probable construction costs were calculated for each proposed improvement.
Capital Improvement Plan (CIP)
Using the above-referenced criteria, GIS, and HouStorm, proposed modifications to the storm sewer systems in the Study Area were determined. Probable construction costs associated with the proposed improvements were determined based on unit cost information obtained from previous storm sewer projects constructed in the City. Unit costs include the following:
The rates do not include any cost allowance for major utility relocations, complete pavement replacement, or acquisition of additional rights-of-way. Furthermore, the cost of hydraulic impact mitigation on receiving bayous or streams is not included. A category and group classification was developed to help prioritize proposed modifications. Storm sewer systems that were determined to be inadequate for the 2-year storm event, and for which flooding complaints had been reported for any storm event, were placed in the highest category. The following category system is used in the CIP.
Category 1 Category for existing storm sewer systems that have been determined to be inadequate, based on the computer analysis program results and flooding complaints that have been reported within the systems drainage boundary.
Category 2 Category for converting existing open-ditch systems (non-storm sewer areas) to storm sewer systems where previous flooding complaints have been reported. Proposed storm sewer systems for this category type address the main trunk system requirements only.
Category 3 Category for existing storm sewer systems that have been determined to be inadequate and flooding complaints have not been reported within the systems drainage boundary.
Category 4 Category for converting existing open-ditch systems (non-storm sewer areas) to storm sewer systems where previous flooding complaints have not been reported. Proposed storm sewer systems for this category type address the main trunk system requirements only.
Category 5 Category for areas currently considered as undeveloped and having no defined drainage system. For this category type, drainage areas and main (trunk) sewer systems were determined. It is expected that these areas will be developed by others in the future.
Category A Category for existing storm sewer systems that have been determined to be adequate. These systems may or may not have reported flooding complaints.
Within each category, each storm system was further grouped to reflect the type of flooding complaint. Systems for which both structure and street flooding were reported were placed in the highest group in the highest category.
Group 1 Systems that have reported structure and street-related flooding complaints.
Group 2 Systems that have reported structure flooding complaints only.
Group 3 Systems that have reported street flooding complaints only.
Group 4 Systems that have no reported flooding complaints.
The percentage of land-use types within each storm sewer system drainage area was determined, as another means to group costs for proposed modifications. The percentage of land-use type was determined using the Land Use classifications and address information obtained from the City’s Planning Department. The addresses were for each lot located within the City of Houston.
The CIP proposed modifications are for conceptual designs only, and do not include sufficient required details for final construction. Prior to final design of the proposed improvements, a more detailed analysis will need to be conducted by future design engineers or consultants to verify conditions used for the CIP.
An engineering consultant team led by Thompson assisted the City of Houston in developing this web-based GIS. The participants in the consultant team, and their roles, include:
Recommended CIP improvements can be displayed within the web-based GIS using one of two available viewers: EasyView or ProView. EasyView allows the user to search the database using a simple "pull down" query. The user can limit the query search based on watershed, council district, group classification, category classification, 2-year CIP cost range, and drainage system inadequacy. If the user selects to use ProView, a separate web window opens and allows a user with GIS experience to view and query. The GIS viewer contains layers that present the following in "plan view":
Detailed project information concerning proposed CIP improvements, including new pipe size changes proposed for existing and new storm sewer systems, can be obtained by using the storm sewer GIS specifically developed for this project.
DISCLAIMER
The data used to prepare maps, exhibits, tables, and analyses for this product was derived from various sources. Thompson provides no warranty and does not accept any responsibility for data used for purposes other than those intended by this product. Any liability or risk associated with such use shall be the responsibility of said user.