Storm Drainage and Flood Protection

Provision of adequate drainage for built-up areas, lots, streets and open areas is essential to protect susceptible land uses and activity areas from property damage, injury or loss of life caused by standing or flowing water. The level of protection needed depends upon the magnitude of potential loss. For example, residential and commercial areas require a high degree of protection from flooding, while parks and outdoor recreation areas may need minimal protection and in some cases can actually serve as temporary drainage areas during unusually high rainfall events.

Storm Drainage Improvements

Topography and man-made obstructions combine to define a drainage basin which is the total surface land area in which water will collect naturally. Drainage facilities include drainage swales and channels, curb and gutters, storm drain inlets, enclosed storm sewers, open ditches, and natural water courses. Each component of the drainage system must have sufficient capacity to accommodate the runoff water discharged to it by upstream components of the drainage system, for the rainfall event the system is designed to serve. The average frequency of rainfall occurrence determines the degree of protection afforded by a storm sewer system. For example, storm sewers in residential and commercial areas are typically designed to accommodate the predicted runoff from a rainfall event expected to occur at least once in five years. Larger, less frequent events will exceed the design capacity of the storm sewer system, resulting in temporary street flooding. Major drainage channels are typically designed to accommodate flows resulting from a rainfall event expected to occur at least once in 25 to 50 years or more. Habitable buildings are required to be constructed with the lowest habitable floor located at or above the level of flooding expected to occur at least once in 100 years. These elevations are specified to be at a finished floor elevation of 24" above curb for a flood zone A and 18" for a flood zone B. A flood zone A is a Federal Emergency Management Agency (FEMA) designation indicating that it is an area expected to flood with a 100 year frequency event. A flood zone B area is expected to flood with a 100-500 year frequency event, and a flood zone C is an area of minimal or no flooding.

Existing Drainage Conditions

The Harlingen area is located within the watershed of the Arroyo Colorado. Except for areas along the steep banks of the Arroyo Colorado and the embankments of raised irrigation canals and drains, the terrain is generally flat. The grade of the land surface slopes very gently toward the coast at an average grade of about 1 foot per mile. Soils in the northern and western parts of the Harlingen area include slowly permeable, loamy soils that provide good drainage. Soils in the central and southern parts of the area include soils that are slowly permeable clayey soils with poor drainage. The subtropical climate has dry winters and hot, humid summers, with average annual rainfall of about 26 inches. Most precipitation occurs in summer thundershowers and intense rainfall associated with tropical depressions and cyclones (hurricanes) that characterize the Gulf Coast from June to October, although nearby landfall of major storms is infrequent.

Upstream control of flow in the Arroyo Colorado contributes to the lack of severe flooding conditions in the Harlingen area. The Arroyo's flow is a regulated amount of the flow of the Rio Grande River, which is controlled by the North Floodway diversion structure.

The urbanized portion of the Harlingen area is served by existing storm drainage facilities that include an extensive underground storm sewer system. The storm sewers vary in dimension from 12 to 60 inches in diameter. Open drainage ditches also exist in many parts of the urbanized area. Nearly all of the developed area drains into the Arroyo Colorado, which flows northeast into the Laguna Madre. The northern part of the city drains into Drainage District #5's North Main Drain which in turn drains into the North Floodway.

Coordinating Agencies

There are four local agencies whose boundaries significantly overlap the City of Harlingen boundaries and whose function pertains to drainage within the planning area (See Figure 8-1 ). The two located in Harlingen are Cameron County Drainage District #5 (CCDD #5) and Harlingen Irrigation District #1 (HID #1). Both agencies currently office at 301 E. Pierce in Harlingen. CCDD #5 is established to construct, improve and maintain open drains and to provide adequate drainage and drainage outfalls within its boundaries. This does not include storm sewers, storm retention or detention basins serving an area less than 640 acres. Acceptance of drainage ditches is formally acted upon by the District Board. HID #1 was formed in 1914 by Cameron County Commissioner's Court and maintains 140 miles of drain ditches that divert flood waters to the Arroyo Colorado or downstream drainage districts. Fifty miles of this system is under the jurisdiction of Cameron County Drainage District #5. The other two agencies are Cameron County Drainage District #3 and Harlingen Irrigation District #1. Both of these agencies currently reside in San Benito at 216 S. Sam Houston. These agencies have similar missions to their sister agencies located in Harlingen. The primary division line between these districts is the Arroyo Colorado.

Flood Plain Management Requirements

Historically, flooding has not been a widespread problem, although intense rainfall occurring in short periods of time will cause some shallow flooding of roadways and poorly drained areas. Major flooding conditions are associated with the landfall of hurricanes along the Gulf Coast of South Texas and Northern Mexico. Major flood damages have not typically been suffered in the Harlingen area, although the potential clearly exists. Future development must not be allowed to encroach upon the identified flood hazard areas.

Identified Flood Hazard Areas

Flood hazard areas in the Harlingen area are identified by the Flood Insurance Rate Map prepared by the National Flood Insurance Program, Federal Emergency Management Agency. The identified flood plain areas are shown in (Figure 8-2 ). The map shows areas of the 100-year flood and areas between limits of the 100-year flood and the 500-year flood.

Flood hazard areas generally occur upstream of structures across the tributary drainage channels to the Arroyo Colorado and areas of shallow flooding due to limited capacity of drainage facilities. Debris such as trees and trash washed away during storm events that collects under bridges or blocks inlets and culverts may obstruct flow and aggravate flooding and drainage problems.

Other areas of poor drainage are known to exist in the Harlingen area where storm sewer lines and drainage ditches need increases in capacity to provide adequate drainage. These local drainage problem areas are not necessarily identified on the official flood hazard area maps prepared by Federal and State agencies. Information on local drainage problem areas are presented in the next section. This information along with available flood plain maps should be utilized in planning and development decisions.

Floodplain Management

Strategies and tools for floodplain management generally include four major options:

1. Modify Flooding - Construction of dams and reservoirs, dikes, levees, floodwalls, channel alterations, diversions, land treatment, or on-site detention are traditional methods of protecting property and saving lives. These measures are effective up to a point, but leave the risk of flooding losses elsewhere and for potential rare flood events surpassing their protective ability.

2. Restore the Natural Floodplain - Avoiding development within floodplains is the best way to protect against flood damages. Tools include Federal, State and local floodplain regulations, information and education, tax incentives, and proper land use planning.

3. Reduce Susceptibility to Floods - Nonstructural measures for reducing flooding problems include sound development policies for private and public development, flood warning and forecasting, disaster preparedness, floodproofing of buildings and structures, and proper enforcement of floodplain regulations.

4. Minimize Impacts of Floods - Nonstructural measures for minimizing flood losses include flood emergency measures, public information and education, flood insurance, flood recovery assistance efforts, and tax incentives for proper floodplain management.

Awareness of flood hazards and use of appropriate floodplain management policies and techniques are inherent in the purpose, goals, and policies for the Vision 2020 Comprehensive Plan. The Future Land Use Plan recognizes identified flood hazard areas and directs future development away from these areas, unless appropriate floodproofing and elevation of buildings and structures is incorporated pursuant to Federal, State and local requirements. Reducing future potential flood losses requires more than structural measures, but should also include protection of the natural floodplain from inappropriate development and manmade obstructions. The City of Harlingen's floodplain management program integrates the available strategies and tools for short and long-term actions and programs to serve the community.

Drainage Improvements Completed and Remaining Needs

Over $2.5 million has been dedicated to addressing drainage improvement needs identified in the original version of the Vision 2020 Plan. ( Figure 8-3 ) depicts the areas originally identified as problem areas in the Plan with a shaded overlay on those areas that have been partially or wholly addressed.

The area originally identified as "M Street Downtown Areas east of Commerce Bowie School Area/West Jackson & Van Buren" has been partially completed. For this update, the large area will be broken into two separate improvement needs because the area west of Commerce Street is being largely funded by Community Development Block Grant (CDBG) funds due to the area being in a qualified census tract. This area will continue to be called West Jackson & Van Buren Area. The area east of Commerce will be called Downtown Area. Improvements have been made to the West Jackson & Van Buren Area along Commerce Street starting at Taft running parallel with the railroad tracks to Buchanan where it goes under the irrigation canal on the east side of Commerce and continues north on Commerce to Filmore Street. Improvements continue under the railroad tracks with two 72" pipes west on Filmore to 1st Street. Junction boxes are in place on West Street connecting to two 7' x 6' culvert boxes running side by side. This project will continue in three more phases which will eventually extend the culvert from 1st Street to "K" Street and will take approximately 3 ½ more years to complete at an estimated cost of $2,500,000*.

The area east of Commerce known as the Downtown Area is not eligible for CDBG funding and has not yet been addressed. The City has a Capital Improvements Board who oversees a program of work compiled by City Staff which is intended to eventually become a Capital Improvements Program (CIP) and this project has been identified as one of the projects for the CIP and is estimated to cost $1,222,500.

The area identified as "Northwest Area" has not yet been addressed and has been identified as a CIP project which will require additional storm drain and drainage ditch installation at an estimated cost of $1,365,100.* In addition, this area is located in a qualified census tract area and can possibly be funded with CDBG funds.

The area identified as "Taft & 3rd Street Area" has been partially completed with installation of reinforced concrete pipes at a cost of $110,000. The Filmore interceptor to be installed in the West Jackson/Van Buren area should address the remaining problems in this area.

The area identified as "Seventh Street and Bowie Avenue" has not been addressed and is proposed as a CIP project which will require a proposed storm drain at a cost of $304,850.

The area identified as "Lemoyne Gardens New Combes-77 Sunshine Strip-Matz Avenue" is really two separate projects. This update will break the two into "Lemoyne Gardens" and "New Combes - 77 Sunshine - Matz Area". The "Lemoyne Gardens" project has been completed by adding a series of storm drain lines and connecting to an open ditch east of FM507 north of Loop 499. This project cost $135,000 to complete.

The area defined as "New Combes - 77 Sunshine - Matz Area" has not been completed but is identified as a CIP project which will require two storm drains at a cost of $440,900.

The area identified as "Sunshine Country Club Estates" has been addressed by CCDD #5 and a private developer. A detention pond was installed and drain pipe bottlenecks under the roadways in this area were enlarged. This system was connected to the North Main ditch which was also enlarged in this area.

The area identified as "Lewis Lane/Ed Carey Drive/Louisiana Street" consists of two separate geographical areas and should be identified as two projects in future maps. It will be broken into the "Lewis Lane Area" and the "Ed Carey/Louisiana Area". The Lewis Lane Area" is currently being addressed by the Texas Department of Transportation (TxDOT) as part of the construction of the US 77/83 Interchange in this area currently ongoing. The "Ed Carey/Louisiana Area" is expected to be addressed by TxDOT as part of the widening of Expressway 77 expected to be started within 18 months.

The "Green Acres" area was previously highlighted on the map but not identified by name. This project is proposed to have additional storm drain at an estimated cost of $247,500.

The Lincoln & Grant ditch shown on the original map was completed by tying into an existing 30" storm sewer line with some additional lateral lines at a cost of $75,000.

The V-Line Drainage Ditch is being constructed by digging a 16' deep drainage canal with precast concrete boxes at road intersections and tying into an existing open ditch on the east side of FM 509. The project thus far has cost in excess of $950,000 through the completion of phase 3 under FM509 to connect to the U-Line open ditch. Phase 4 is about to begin and will cost an additional $450,000 to build three structures which will cross under Haine, FM509 and Line 19 to connect to the Arroyo Colorado.

While many of the drainage issues originally identified are still existing, it is important to note that this is a 25 year plan and that those areas identified as drainage problems have existed for many decades. It is extremely expensive to address comprehensive drainage needs. For this reason it is imperative that proper subdivision and building permit controls regulate future drainage of new development to prevent creation of significant new areas of drainage problems.

Drainage Improvement Needs

A revised map of remaining drainage problem areas existing and storm sewer system improvement needs is shown in (Figure 8-4 ). The drainage improvement plan includes planned major storm sewer system improvements to major drainage channels. The existing drain ditches and associated drainage area boundaries for areas served by these planned system improvements are also shown. The identified drainage problem areas include the following general vicinity locations:

• Downtown Area east of Commerce;
• Northwest Area;
• New Combes - 77 Sunshine Strip - Matz Area;
• Sunshine Country Club Estates;
• Lewis Lane;
• Ed Carey/Louisiana Street;

The sources for the storm sewer improvement plan include the "Evaluation of Drainage Problems for the City of Harlingen", which was performed by Martin & Brown Engineering in October 1992, comments from CCDD #5 Manager and CCDD #5 District Board, and modifications completed since the adoption of the original plan as reported and completed by the City of Harlingen's Public Works Department.

Goals and Objectives

The goals and objectives for the Drainage Element of the Vision 2020 Comprehensive Plan are outlined in this section. Goals and objectives were developed based upon the planning analyses and citizen input received during the plan development process.

Goal 8.1 Exercise sound management for floodplain areas and stormwater drainage.

Objective 8.1.a Minimize the potential for flood damaages to existing and future development by requiring proper finished floor elevation designation on final plats and in new construction plans.

Objective 8.1.b Maintain and enforce a floodplain management program in conformance with the regulations and guidelines of the Federal Emergency Management Agency and the National Flood Insurance Program.

Objective 8.1.c Maintain up to date training of the City's Floodplain Administrator as provided by qualified agencies.

Objective 8.1.d City and CCDD #5 should cooperate to obtain letters of map amendment for flood areas to FEMA.

Goal 8.2 Maintain and efficiently utilize existing drainage and flood protection infrastructure.

Objective 8.2.a Support adequate public funding availability to ensure drainage system development, operation and maintenance. This should include developer participation and/or provision as needed to serve their developments.

Objective 8.2.b Regular maintenance should be performed to maintain the water carrying capacity of drainage facilities, including removal of trees, trash, sediment, and other debris or obstructions.

Objective 8.2.c Upgrade existing drainage facilities by concrete lining ditches where technically and economically feasible.

Objective 8.2.d Planning for new development and redevelopment should include analysis of storm drainage impact and identification of drainage improvements needed to accommodate increased stormwater runoff.

Objective 8.2.e Coordinate floodplain management and drainage improvement planning with other governmental agencies responsible for stormwater management in adjacent areas.

Goal 8.3 Promote fiscally responsible growth that can be efficiently served by infrastrcture.

Objective 8.3.a Acquire additional right-of-way necessary to construct future storm drainage and flood protection improvements through subdivision processes.

Objective 8.3.b Require development to incorporate adequately designed drainage improvements, including appropriate use of detention ponds to reduce discharge of stormwater to the rate that can be accommodated by the downstream drainage system.

Goal 8.4 Ensure proper infrastructure to provide enhanced quality of life.

Objective 8.4.a Construct remedial improvements to provide adequate storm drainage for known areas of poor drainage within the city.

Objective 8.4.b Prepare and maintain an up-to-date storm drainage master plan for the Harlingen area, and implement the recommended improvements in cooperation with other governmental jurisdictions.

Objective 8.4.c Coordinate with the Texas Department of Transportation (TxDOT) when constructing new transportation corridors to ensure adequate drainage needs are planned to prevent future costly increases.