A growing Wisconsin village factors future development into its current storm and sanitary sewer management plans.

By Michael F. Campbell

Approaches to stormwater management vary throughout the United States. Because numerous factors affect these management plans–soil conditions, climate, current and projected population density, existing facilities and their state of repair, and economic conditions within a specific boundary–they are among the most important, complicated, and costly plans with which local governments must deal. The stormwater management plan produced for the village of Menomonee Falls, WI, illustrates how one community tackled its stormwater problems in a comprehensive, multifaceted way.

Menomonee Falls is a thriving, picturesque suburb of Milwaukee in southeastern Wisconsin. Similar to most villages in this region, it was settled in the mid-1840s. Appleton Avenue, the village's main arterial highway, was originally an Indian path. The influx of people into the area is still visible today, and the 2000 Census confirms that the village is the third fastest-growing municipality in southeastern Wisconsin, with its population leaping from 26,840 in 1990 to 32,647 in 2000.

The village's 33.2 mi.² are crisscrossed by abundant water resources and transversed by a subcontinental divide separating the Mississippi River drainage basin from the Great Lakes—St. Lawrence River drainage basin. Specifically, the part of the village west of the subcontinental divide is in the Fox River watershed; the area east of the divide is in the Menomonee River watershed. The fact that the water supply for the village has its source at, and must be returned to, different drainage basins complicates any stormwater management plan.

This peaceful community, with more than 6 mi.² of environmental corridor and numerous rivers and streams, received two very rude wake-up calls that jolted the village's leadership into looking at stormwater management in a whole new light. On June 20 and 21, 1997, 8.4 in. of rain fell in 26 hours. Of this total, 5.87 in. fell in 10 hours. The storm had a recurrence interval estimate at more than 500 years. Thirteen percent of the total properties in the village experienced basement flooding. Slightly more than one year later, on August 5 and 6, 1998, more than 4 in. of rain fell in 37 hours. Of this total, 2.93 in. fell in six hours. The recurrence level of this storm was estimated at 15 years.

This "one-two punch" prompted Village President Joseph J. Greco, Village Manager Dick Farenkopf, and Utilities Director Max Vogt to reevaluate the village's existing stormwater and sewer facilities and take an aggressive, comprehensive look at how to avoid severe flooding problems. "It was very apparent that something had to be done. To do nothing was not an option," says Greco. "We had many residents who had experienced a great deal of damage, and the elected officials were expected to resolve the problems."

The village hired the Waukesha, WI, engineering firm of Ruekert/Mielke to complete both a stormwater management system plan and a companion sanitary sewerage system plan. Because the plans are so closely interrelated, the stormwater management plan, if fully implemented, would significantly reduce clear-water inflow into the sanitary sewerage system during excessive rainfall events, reducing both sanitary sewer surcharging and the backup of sanitary sewage into the basements and the need to bypass untreated sanitary sewage into the environment. "Because the plans were completed simultaneously, the village can address the problems in a holistic fashion," notes Project Engineer Kurt Peot. "The village now knows how these studies work as companion pieces, so projects can be linked together for economic, environmental, and construction reasons."

The first step was a complete evaluation of existing conditions: mapping the area, identifying land use, charting topography, analyzing surface drainage patterns and geology, and studying the climate, water supply, and existing sanitary sewerage and stormwater management systems. A seamless, digital base map of the entire stormwater management planning area was generated using available large-scale topographic and cadastral base maps and integrating them with geographic information system technology.

Property owners in the village were also surveyed soon after the last significant rainfall event. Of 10,752 questionnaires distributed, 5,306 were completed and returned. The questionnaire served to gather information about basement flooding, depth of the water, and whether clear water or the backup of sanitary sewage caused the flooding. It also identified properties that experienced flooding as a result of a power failure and the subsequent loss of basement sump pump operation. The 49% return rate on the survey was helpful in pinpointing problem areas.

In studying existing land use it was found that about 44% of the area was in urban use and about 56% was in rural use. But because the village continues to transform into a more urban environment, leaders chose to institute tough guidelines. They wanted their ordinance to require that the rate of runoff generated by a 100-year rainfall event under proposed development conditions be restricted to the rate of runoff generated by a two-year recurrence under existing land-use conditions. Therefore, in the undeveloped western area of the village, the hydrologic analysis provided flows attendant to the two-, 10-, and 100-year rainfall and existing land-use conditions for use in evaluating developments as they occur. In the developed eastern area of the village, however, the hydrologic analyses provided flows attendant to the 10- and 100-year recurrence and planned 2020 land-use conditions with the goal of containing the minor storms (10 years and smaller) within the existing network of storm sewers, roadside ditches, and culverts. Part of the goal was to also provide adequate facilities for the major storms up to the 100-year event by providing overland flow paths consisting of swales and street rights of ways without flooding homes or businesses.

The existing sanitary sewerage system consists of 169 mi. of gravity flow sewers, 4,140 manholes, 9,000 building service connections, four pumping stations, and seven metering manholes. The existing stormwater management system has approximately 94 mi. of concrete and corrugated-metal gravity flow storm sewers, 1,810 manholes, 3,609 catch basins, 844 inlets, 60 detention ponds, and 558 culverts. Compiling the data for the study was a challenge in itself. Sanitary sewer system records were complete, and the information was supplemented with field locations of manholes. Storm sewer records were spotty at best, however. Extensive fieldwork gathered information on the location, sizes, and types of manholes and catch basins, culverts, detention ponds, and outlet structures. This effort was cost-effective because of the use of global positioning system technology. Because fieldwork was being used for this inventory, the village gathered information on the water system at the same time. The end result was an updated digital system of all village utilities rather than stand-alone records.

The information was entered into a public works management information system created for the village by the Ruekert/Mielke Technology Services Department. This comprehensive inventory not only helps the village assess its current facilities and allows for planned maintenance but also is key to anticipating future build-out conditions and the resultant changes needed to avoid problems.

The village and the engineering firm worked closely with the Southeastern Wisconsin Regional Planning Commission, which had previously issued flood-control plans for both the Fox and Menomonee Rivers and which reviewed the village stormwater management plan. Reports Phil Evenson, the commission's executive director, "The village's stormwater management plan represents a good example of integrating solutions for local stormwater drainage problems within the framework of watershed flood-control plans."

These two watershed plans were helpful, but stormwater inundation and riverine area flooding differ in significant ways. Stormwater inundation involves water moving downslope toward major rivers, such as the Menomonee and Fox, and flooding is caused by water moving in the opposite way. In contrast to areas experiencing flooding when drainage areas can contain tens or hundreds of square miles, stormwater inundation usually occurs in isolated, scattered pockets.

All of the drainage basins in Menomonee Falls were subdivided into individual sub-basins and analyzed. Junctions in the system, changes in sewer pipe diameter, and runoff flows were calculated at each key point along the line and compared to the existing capacity of the system at that point. When the flows were found to exceed the capacity of the conveyance facilities, or were expected to exceed capacity under full build-out conditions, it was noted in the study, and alternative means of reinforcing the system were identified and analyzed.

The study highlighted multiple alternative plans, including existing system alternatives, water-quality objectives, and critical land uses. Advantages and disadvantages of all the alternatives were clearly outlined so that village officials could make informed decisions that meshed with necessary repairs and upgrades. "Some of the infrastructure in Menomonee Falls is quite old," Peot notes. "As this infrastructure is replaced, construction can include both sewerage upgrades and stormwater management elements at the same time. There's just no sense in digging up a road one year for sewer lines, then returning a year or two later and adding the stormwater management components. It is inconvenient and expensive, compromises public safety, and leaves the village open to more flooding should another significant rainfall event occur between projects."

The meat of the study lies in comprehensive lists of capital improvements and annual operating and maintenance costs. Projects are ranked according to priority, based on the number of basements that experienced flooding, and are broken down into very specific areas within the village. Because the study meshes with land-use plans for 2020, the impact of development and potential future problem areas can be identified and acted upon in advance. New construction can be evaluated for its impact on a particular area, and the village planning staff and plan commission members can act accordingly.

The goals of the study were to eliminate surprises, both for the current administration and for future elected officials, and to help avoid catastrophic flooding and property damage of the type that occurred in 1997 and 1998. The plan is expected to keep the village on track for many years, rather than having to deal with either economic or environmental uncertainties. In addition to the construction of projects, the plan also provides three alternative plans for funding: one based on cash financing, one based on debt financing utilizing general obligation bonds, and the third based on the formation of a stormwater utility district and user charges.

As a result, two top-priority projects have been constructed, a third is under construction, and two others are being designed. Greco adds, "We have aggressively attacked the problems and we have seen results. However, there still remains much work that needs to be done." The village is working to implement a stormwater utility to provide stable funding for the stormwater components in a way that is equitable for taxpayers. Major and minor system components will function together and significantly reduce both infiltration and inflow and sanitary sewage surcharging. The plan will also protect water quality and enhance habitat for wildlife. Ruekert/Mielke has been honored by the Wisconsin Association of Consulting Engineers for its work on the study.

Michael F. Campbell, P.E., is senior vice president and chief operating officer of Ruekert/Mielke Inc., a multidisciplinary engineering firm in Waukesha, WI.

SW - November/December 2002

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