SECTION V - CAPITAL IMPROVEMENT PLAN

A. PURPOSE OF THE CAPITAL IMPROVEMENT PLAN

The purpose of the CIP is to give the City a tool to plan future capital improvement expenditures for storm sewers within the City. To do this, each CIP identifies the general characteristics of proposed drainage modifications or improvements required for drainage systems that are currently considered to be inadequate relative to present City of Houston storm drainage design criteria. The drainage system consists of existing storm sewers, roadside ditches, and a combination of the two. In addition, this CIP includes general drainage requirements for areas where no defined drainage system exists. According to City of Houston design criteria, as presented in the previously referenced Design Manual dated October 1999, storm sewers should be designed for the 2-year rainfall event.

The CIP proposes modifications for conceptual designs only, and does 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, especially with regards to specific project impacts and any required mitigation thereof.

B. PROPOSED CIP

1. CIP Development Procedures

To determine proposed CIP requirements, storm sewer systems were analyzed using HouStorm and the web-based GIS. Proposed CIP requirements were determined for storm sewer systems located within the City of Houston. This includes areas within Harris and Fort Bend counties. The HouStorm program is described in Section IV - HouStorm. A summary of the storm sewer analysis results for each existing storm sewer system analyzed can be viewed in the GIS. More specific, detailed site information on existing conditions will be needed prior to final design and construction of any proposed improvements.

2. Existing Storm Sewer System CIP

As previously referenced, proposed storm sewer modifications for existing storm sewer systems were determined using the 2-year storm event. Proposed storm sewer modifications also considered the following:

• Modifications of existing storm sewers would consist of increasing pipe diameters.
• Replacement of existing storm sewers with smaller pipe diameters would not be proposed.
• Proposed storm sewer type would consist of reinforced concrete pipe or boxes.
• Wherever possible, invert elevations and alignments for existing storm sewers would be used for proposed storm sewer systems.
• The computed hydraulic gradient (HG) should not be more than a maximum of 2 feet below the manhole rim elevation or natural ground elevation. If the computed HG elevation is more than 2 feet, a system should be proposed to replace the undersized pipes.
• For pipe diameters greater than 108 inches, box culverts of similar hydraulic capacities were considered.

Due to lack of information concerning inlets and inlet leads, proposed CIP modifications do not include either the evaluation of inlets or modification to existing inlets, although the HouStorm program has an extensive engine with the capability of modeling inlets and their affect on roadway ponding width and depth.

3. New System CIP

For areas currently drained by roadside ditches, a storm sewer system (major trunk line) was proposed to replace existing roadside ditch systems. In addition to the previously mentioned criteria for CIP improvements, the following factors were also considered for the roadside ditch areas:

• The proposed storm sewers would consist of only the main (trunk) sewer system.
• Proposed storm sewer system alignments would follow existing streets and roadside ditch patterns wherever possible.
• The maximum gutter run of 500 feet was considered when determining the alignments of proposed storm sewer systems.

4. GIS Layers

The CIP identifies general characteristics of improvements for most of the storm sewer systems located throughout the City. Within the web-based GIS, the following layers can be displayed:

• Existing and proposed storm sewer system alignment and size
• System identification number
• System drainage area boundary
• Existing drainage ditches and detention basins
• Approximate location of flooding complaints (City survey)
• TSARP floodplain and floodway boundaries and Base Flood Elevations (BFEs)
• FEMA repetitive loss properties
• HGAC’s digital ortho photographs
• City Council district boundaries
• Parcel boundaries (HCAD)
• Land use patterns
• Water and wastewater lines

C. CAPITAL IMPROVEMENT PROGRAM COST

1. Unit Probable Cost Rates

Probable costs associated with storm sewers included in the CIP were determined using unit cost rates from City of Houston Bid Tabs taken from ten storm sewer projects constructed between 1994 and 1998. The sewer pipe diameters in the Bid Tabs ranged from 24 to 102 inches. The unit cost rates are given in linear feet for each pipe diameter. The costs for the pipe diameters greater than 108 inches were extrapolated from the bid tabs.

The unit probable cost rates for proposed storm sewer system modifications include the following:

• Removal of existing sewer pipe and pavement
• Storm sewer pipe
• Manholes
• Inlets
• Replacement of pavement
• Dewatering
• Trench safety
• Traffic control
• Engineering and contingency costs (20 percent)

Costs for proposed storm sewers do not reflect the following:

• The relocation of existing utilities due to construction of new storm sewers
• The acquisition of additional right-of-way that may be required

2. Category and Group Classifications

A category and group classification was developed to help prioritize proposed CIP modifications in order to distinguish between systems that need to be modified relative to not meeting design criteria or in consideration of previously reported flooding records. At the conclusion of the analysis of all of the storm sewer systems, the systems were categorized and grouped by incorporating the drainage system types and flooding complaint information. The following represents the category and group system used in the CIP, for which six category classification types were developed, and includes a description of each category classification type.

Category 1 Existing storm sewer systems that have been determined to be inadequate and where flooding complaints have been reported within drainage boundaries

Category 2 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 Existing storm sewer systems that have been determined to be inadequate and where flooding complaints have not been reported

Category 4 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 Areas currently considered to be undeveloped and having no defined drainage system
For this category type, drainage areas and main (trunk) sewer systems were determined. An assumption was made that these areas would be developed by private developers in the future. The purpose of evaluating Category 5 areas was to determine generally what drainage improvements would be required.

Category A Existing storm sewer systems that have been determined to be adequate. These systems may or may not have reported flooding complaints.

For each category type, except for Category A, costs for proposed improvements were determined. To help further group the costs required for proposed improvements, the following Group Cost Classifications were developed for each category. The Group Cost Classifications were determined by overlaying the flooding complaint data with the storm sewer data, and then completing a query.

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. Group 4 cost types will be applicable for Categories 3 and 4 only

As another means to group the proposed modifications, the percentage of land use types within each storm sewer system drainage area was determined, using the previously referenced land use GIS and data obtained from the City’s Planning Department. The Planning Department data included an address for each lot located in the City of Houston. The land use database file was overlaid with the address information, resulting in a land use type being assigned to each address. The number of addresses within each drainage system was then determined. Results of determining the number of addresses within each system can indicate the approximate number of land use types, such as single-family units, that could be affected by improvements proposed within the system.

It was assumed that costs for Category 5 areas would be developed and funded by others in the future, thus requiring no City funds for proposed drainage improvements.