Development of a Stormwater Master Plan
The City of Maryland Heights, MO, a suburb in the St. Louis metropolitan area with a population of approximately 25,500 people, recently undertook a major study to develop a comprehensive stormwater master plan to solve erosion and flooding problems associated with increased urbanization. The plan accomplished four major objectives. First, it identified major problem areas based on citizen complaints and the subsequent development of capital improvement projects to alleviate the stormwater problem areas. Second, it implemented funding sources for the capital improvement program, including a half-cent sales tax increase dedicated to stormwater and parks improvements and a 319 nonpoint-source-pollution Department of Natural Resources/Environmental Protection Agency grant that provided 60% of the funds for the Midland Creek Bank Stabilization Project. Third, the development of an XP-SWMM computer watershed model that supplemented a similar model being done for the Metropolitan St. Louis Sewer District, a local stormwater jurisdictional authority. Fourth, the formation of a citizens’ stormwater committee to develop a ranking system for prioritizing stormwater projects in an equitable and cost-effective way that minimizes subjective factors. The plan had to be understandable to the community to eliminate sociopolitical factors that could influence the actual implementation of projects. Several priority-ranking procedures used by other communities were analyzed to see if they met the objectives stated above. The prioritization system chosen combined the best features of all the plans, produced consistent results independent of the evaluator, and was easy to explain to the public. It also reflects the community’s values as determined by the committee in ranking stormwater projects.
The city’s total land area of 22.7 mi.2 stretches from the Missouri River on the west to Lindbergh Boulevard on the east and is generally bounded by Creve Coeur Mill Road to the north and Page Avenue to the south. Although a small portion of the city drains to the Creve Coeur Creek Watershed, the majority of the land area is divided between the Missouri River floodplain and the Fee Fee Creek Watershed. Because development in the floodplain is limited, the city’s plan focused on the 65% of the land area that lies within the Fee Fee Creek Watershed.
The Fee Fee Creek Watershed, shown in Figure 2, is 14.6 mi.2 in size and located in northwest St. Louis County. The watershed drains to the northwest, with the main branch of Fee Fee Creek discharging into Creve Coeur Creek at the edge of the Missouri River floodplain. Figure 3 shows the primary stormwater management system (PSWMS) in the watershed. In general, natural, unimproved channels drain most of the Fee Fee Creek Watershed with small reaches of storm drains within subdivisions. There are no significant lengths of improved open channels. Fee Fee Creek consists of a main branch and three major tributaries. The PSWMS contains 13.1 mi. of Federal Emergency Management Agency (FEMA) Zone “A” streams and approximately 3.9 mi. of upstream open channels. In addition, the watershed contains a total of 7.2 mi. of known storm sewers with a diameter of greater than or equal to 36 in.
The Metropolitan St. Louis Sewer District and the SSMIP
The Metropolitan St. Louis Sewer District (MSD) is responsible for both combined and separate sewer systems within its boundaries, which encompass a total of 524 mi.2 and 92 municipalities, as well as unincorporated St. Louis County. Annexation of these additional areas increased stormwater responsibilities and brought about a multitude of drainage-related problems and their associated public demand for solutions, despite the fact that revenues collected in the newly annexed areas provided little money for these solutions. To respond to the needs of residents throughout the district, however, MSD initiated the Stormwater System Master Improvement Plan (SSMIP). Among the goals of the MSD study were calculating detention basin release rates to prevent further deterioration of downstream properties and creating a prioritized list of capital improvement projects that could be implemented once funds were available. Since this effort focuses on a watershed approach, the Fee Fee Creek Watershed was included as one of the study areas. Study of the Fee Fee Creek Watershed coincided with the city’s stormwater plan.
Two factors contributed to the need for the city’s stormwater study. One was that unregulated development prior to the city’s incorporation in 1985 had resulted in the degradation of many of the area’s natural drainage systems. The other was that in the annexed areas, MSD lacked the funds necessary to undertake large capital improvement projects. Since the district chose to concentrate on basic maintenance and emergency responses to failed systems, the burden was on local authorities to take care of their own stormwater problems.
In 1995, Maryland Heights voters approved a half-cent sales tax increase, dedicated to stormwater and parks. To direct Maryland Heights’ stormwater efforts, the city formed a Citizens Stormwater Advisory Committee and authorized funding for a comprehensive study of watershed hydrology and stream hydraulics, problem areas, project alternatives, development of mitigation strategies, environmental considerations and compliance, and establishment of a liaison with the city’s Stormwater Advisory Committee. Because both Maryland Heights and MSD were conducting concurrent studies in the same area, the city’s Stormwater Master Plan was closely allied with MSD’s Fee Fee Creek Watershed Study. This led to shared information that benefited both parties.
The first step in developing the City of Maryland Heights Stormwater Implementation Program was gathering all pertinent information concerning specific stormwater complaints and watershed characteristics. Sources for watershed properties included the St. Louis County Soil Survey, 7.5-minute US Geological Survey topographical quadrangle maps, FEMA flood insurance studies, and MSD facilities base maps and aerial photos. After these sources were reviewed, a consolidated problem/project list was generated to eliminate duplication among the various sources. Known- or potential-problem areas, such as neighborhoods that lacked storm sewers, were noted for further investigation.The fieldwork phase of the Stormwater Implementation Program began on March 5, 1996. Two components comprised this fieldwork: an inventory of the existing drainage systems and investigation of stormwater problem and complaint areas. The initial task of this phase consisted of verifying stormwater structures plotted on MSD facilities maps and visually locating previously unmapped structures and recording them on the MSD maps. Once this was accomplished, pertinent information needed to analyze the system was gathered. For previously unmapped structures, this information included (1) surveying all top elevations; (2) assessing the type, condition, construction, and dimensions of the structures; (3) determining the number and size of all connecting pipes; and (4) recording all data on inspection logs.
Since many mapped structures were missing flow lines or top elevations, crews obtained information as an additional component of their fieldwork. Office technicians transferred information from field notes and field map sketches to unmarked MSD facilities maps and connected structures with pipes. A total of 898 stormwater structures that were not on the MSD maps were identified during this process. In addition, missing flow-line or top elevation data were obtained for 875 structures previously mapped by MSD. These efforts have resulted in more accurate MSD facilities maps and an updated structure database.
Investigation of Problem Areas
To develop a list of potential stormwater projects, the initial focus was placed on approximately 80 stormwater complaints received by the City of Maryland Heights and forwarded to Horner & Shifrin (H&S) in St. Louis, MO. Field crews were sent out to investigate these areas, and they recorded their notes and observations on problem/project review sheets. Problems were sorted into two categories: (1) infrastructure repair and maintenance projects and (2) potential capital stormwater projects. Workbooks for each classification were then assembled. Infrastructure and maintenance projects were returned to the city for disposition while potential capital projects were developed by H&S, including preliminary design and cost estimates.
An additional 88 problem areas that remained from the review of original data were investigated to make sure that these problems still existed. If that this was the case, these sites were also analyzed and solutions developed. These areas also became part of the project list, with preliminary design and cost estimates.
Emphasis was placed on solutions that were environmentally friendly, particularly where urban streambank erosion problems occurred. H&S, along with specialty subconsultant Intuition & Logic of Webster Groves, MO, a suburb of St. Louis, developed mitigation strategies focused on natural biostabilization methods such as composite revetment, branch packing, and joint staking. The goal was to restore the streams, whenever possible, back to their natural state. Fluvial geomorphology studies showed that much of the stream instability was caused by downcutting of the main branch of Fee Fee Creek and the resulting headcutting in its tributary branches.
Mars Lane/Grand Circle Project
The Mars Lane/Grand Circle Project is located on Midland Creek, a 3,800-ft. tributary of Fee Fee Creek. Over the past 25 years, increased flows from urbanization of the watershed lowered the creekbed by as much as 8 ft. from its original elevation, resulting in bank instability and a subsequent widening of the channel. In an attempt to remedy the problem, St. Louis County tried to armor the banks with gabion baskets. Since the county did not address the downcutting that was the actual cause of the bank failure, however, these baskets have since been undermined and have failed to mitigate the problem. To control downcutting in the channel, riprap grade controls are being installed at several locations in the project reach. Bank repair is being done by a variety of methods including:
Construction of a Bankfull Shelf. This entails sloping the existing banks back from the toe at a 1:1 slope to an elevation equal to the two-year storm event and then cutting a horizontal shelf into the slope to allow high-flow storm events to spread out rather than being confined to a narrow channel. The bank slopes again from the bankfull shelf to the top of the bank at a 2:1 grade or milder. The toe of the slope in the channel is stabilized using a rock roll or coir log staked into the streambed. Additional slope protection is provided below the bankfull shelf by joint staking, riprap, or composite revetment. Slope protection above the bankfull shelf is by joint staking and seeding with natural plants and wildflowers.
Composite Revetment. This method slopes the existing bank back from the toe at a 1:1 slope or milder all the way to the top of the bank. Actual slopes are determined based on soil conditions and space limitations. The toe is protected by a rock roll and the slope stabilized by alternating rows of geoweb-wrapped rock and joint-staked plantings protected by a layer of mulch.
Living Crib Wall. A living crib wall is constructed of untreated logs or timbers. The crib is filled with appropriate backfill and layers of live branch cuttings. The live cuttings extend through the backfill into the native soil behind the structure. Once they take root and become established, they help bind the crib wall into a coherent, unitary structure that provides excellent erosion protection.
Branch Packing. This biostabilization technique is used to repair gullies that form from concentrated runoff. It consists of filling the gully with alternating layers of live-branch cuttings and compacted soil. The branch cuttings serve to break up the flow and disperse it over a wider area, reducing the chances of erosion.
Development of a Priority Ranking System
The objective was to develop a ranking system for prioritizing stormwater projects in an equitable and cost-effective way that minimized subjective factors. It had to be understandable to the community to eliminate sociopolitical factors that could influence the actual implementation of projects.
Several priority-ranking procedures used by other communities were analyzed to see if they met the objectives stated above. The system chosen for the stormwater committee’s review closely resembles the prioritization scheme proposed for use in MSD’s SSMIP. A few minor modifications were made by H&S to alter the system to address the specific stormwater problems in the City of Maryland Heights. These modifications included adjustments to the benefit points assigned to various stormwater projects and the addition of point categories for yard erosion, yard flooding, and nuisance street flooding/ponding.
The plan as originally submitted to the stormwater committee used the difference between the project’s cost rank and benefit rank as a scale to prioritize the projects. Although this was later changed by the committee to a benefit/cost ratio, both procedures rely upon a benefit point system to determine the worth of various projects.
Benefit rank is determined by applying a point system that divides benefits into two general categories: (1) stormwater problems resolved and (2) secondary benefits of stormwater projects. For the first category, points are given for each flooding or erosion problem that would be resolved. Points for erosion problems are allotted according to the severity of the problem and for flooding according to the frequency of the flooding event. In the second category, points are given if the stormwater project would provide miscellaneous benefits, such as increased safety. This system can readily incorporate additional criteria or changes in the point allocations to reflect the value judgments of the community.
This feature of the plan was evident when the system was reviewed by the City of Maryland Heights Stormwater Committee. The committee made changes in the plan to reflect the community’s values in applying benefit points to the projects. These included changing the point totals for street flooding, modifying the criteria for yard erosion, and dividing the category for erosion threatening miscellaneous structures into two separate entities. They also made the aforementioned change to a benefit/cost ratio to rank the projects using a benefits-per-thousand-dollars scale.
Once these changes were made, the system was applied to the stormwater projects generated from field investigations. A ranking was drafted and brought back to the committee for review. The committee approved the benefit point system for ranking projects.
Selection of Projects for Budgeting
Once the benefit point system was approved, a review was conducted concerning the assignment of benefit points to the proposed stormwater projects and documentation provided to justify the point totals. Also reviewed and revised at this time were the preliminary design and cost estimates for each project to ensure their accuracy. During the first year, seven projects that were determined to need further hydraulic analysis to ensure that proposed solutions would not cause adverse downstream effects were withdrawn from the prioritization process.
After the review procedure, a prioritized list of projects was generated using the benefit point system. This list was divided into two categories: small projects (those costing less than $100,000) and large projects (greater than $100,000) for the committee’s selection. The city has committed at least 25% of each year’s stormwater budget to small projects so that they do not get overlooked in favor of larger projects. In the first year of the plan, the committee selected 17 capital improvement projects for final design and construction.
Watershed Modeling and Hydraulic Analysis
Using the materials obtained during initial data acquisition, the drainage areas within the major watersheds in Maryland Heights were delineated. Further identification was performed in areas that required specific analysis. Watershed properties, including land-use, soil types, and impermeability, were also determined.Once this was accomplished, computer modeling began on a limited scale. The XP-SWMM stormwater simulation and the US Army Corps of Engineers HEC-1 and HEC-2 models were used. The main purpose of HEC-1 is to simulate hydrologic processes during flood events, which has been done for Fee Fee Creek. HEC-2 is designed to calculate water-surface profiles for steady, gradually varied flow in natural or manmade channels. HEC-2 (and its successor, HEC-RAS) is used as a basis for developing further input into the SWMM Extended Transport simulation. This software can be applied to virtually every aspect of urban drainage-from routine drainage design to sophisticated hydraulic analysis-using both single-event and continuous simulation. By subdividing large catchments and flow routing down the drainage system, SWMM can be applied to areas of all sizes-from parking lots to subdivisions to entire cities-and is especially helpful in analyzing problem areas.
Additional modeling included an updated HEC-2 model to duplicate the results of a 1982 field-initiated study to ensure data accuracy. In addition, SWMM runoff models were run to assess conditions at several problem areas. In 1997, the entire watershed model was completed, which allowed H&S to analyze downstream effects of proposed solutions to stormwater problem areas.
The Federal Nonpoint Source Management Program is authorized by Section 319 of the Clean Water Act Amendments and provides funds to the Missouri Department of Natural Resources for the prevention and control of nonpoint-source water pollution (polluted runoff from unregulated or unpermitted sources). These funds are a potential source of support for locally directed water-quality protection projects that provide up to 60% of the projects’ cost. On behalf of the City of Maryland Heights, H&S submitted an application for the 319 Grant, proposing an innovative bioengineering approach to stabilizing the banks of Midland Creek. Several methods of biostabilization are being utilized, including composite revetment, branch packing, live staking, and coir roll toe protection. The project, which encompasses the city’s Vago Park, stretches for approximately 3,800 ft. from near Fee Fee Road to Grand Circle Drive and is a joint venture of the Public Works Department and the Department of Parks and Recreation. The project has a strong educational component, and the city is working in conjunction with the Pattonville School District to develop this aspect of the enterprise. The grant for $762,000 was awarded on September 12, 1996, the largest amount for that fiscal year.
The Missouri State Legislature has authorized any municipality or county, if approved by the voters, to impose a special sales tax of up to a half cent to fund local parks or stormwater control. Revenue may be used for any local park or stormwater-control activity authorized by the governing body of the county or municipality. Selling this type of tax to the voters is much easier with the inclusion of local parks. Although not everyone sees the benefits of correcting stormwater deficiencies, most people have a more positive reaction when it comes to improving park facilities.
The city splits its revenue evenly between stormwater and parks projects, although it may be divided otherwise if needed. Except for the partial funding received for the Vago Park project through the 319 Grant, all of the city’s stormwater improvement projects have been funded using this revenue. Since its inception, this tax has provided approximately $2 million each year for the stormwater program.
This funding mechanism has been utilized by several municipalities in the St. Louis Metropolitan Area, including the cities of Brentwood, Bridgeton, Richmond Heights, and Shrewsbury.
Public response to the city’s Stormwater Master Improvement Plan has been encouraging. At a public open house held in May 1997, the citizens of Maryland Heights had the opportunity to ask questions about and comment on the plan. The majority of the remarks were very positive, commending the city for taking a proactive stance toward stormwater problems. For the most part, residents were pleased to see their tax dollars being spent as they intended and the stormwater tax actually being used to fund stormwater projects.
