Storm Water & Flood Management

Storm water studies were analyzed in 2016 to provide the Village with potential improvements that could be done to improve uniform storm water service levels across the community. It should be noted that despite the large scale and high cost of the improvements identified, they are not designed to provide complete protection against a storm event similar to what the Village experienced in 2011 when a record-breaking rain event caused flooding issues for many residents. The July 2011 storm event occurred after two weeks of heavy rain had saturated the ground.  If a storm with a similar intensity and duration happens again, it is likely that extensive damage could still occur with or without the implementation of the improvements identified. 

Categorizing Flood Management Projects

One of the challenging aspects of implementing any major improvement plan is being objective for all sections of the Village. This project is no exception. The three studies that were completed were separated into Combined Sewered Tributary Area (CSTA), prepared by CDM Smith, and Separate Sewered Areas (SSA), prepared by Christopher Burke, and a letter report was issued on the Cypress area (also separately sewered).

A combined sewer area drains storm water and waste water within the same conduit through the Village’s combined sewer network discharging to TARP (deep tunnel), and then to the Metropolitan Water Reclamation District (MWRD) treatment plants, while the separate sewered areas drain storm water through storm sewers to a creek/stream, and waste water through sanitary sewers to the MWRD treatment plants.

Each of the areas have unique issues that create challenges in attempting to compare the proposed enhancements. The one issue that is difficult to evaluate is the level of service in the CSTA vs. level of service in the separate sewered area. The CSTA was developed prior to the development of detention basins. The CSTA conveys both rain water and sanitary flows in the same pipe. Within the CSTA, the storm water control (combined sewers) provide between a 10 - 25 year level of service. The sanitary service line that connects a house to the combined sewer will also act as a conduit for excess storm water to enter the house, which is how basement backups occur.

One important finding is that a home in the CSTA can prevent sewer back up from occurring during extreme storm events by installing overhead sewers. As an incentive for homeowners to install an overhead sewer system, the Village offers a program with a rebate of 75% of the cost to install a Village approved Overhead Sewer or approved alternative flood control system up to a maximum of $11,250. In the separate sewered areas, a design for the 100 year storm event is achieved with the installation of storm water control/detention basins.

In analyzing the data received by the three comprehensive flood studies, the Village has divided potential improvements into three categories in relation to the impact of storm water on a home or neighborhood. 

Structure Flooding
Structure flooding has the most negative impact to homes. Once water enters the lower level of a structure, the potential damage can range from walls, furnaces and water heaters to personal belongings such as furniture, stored items and floor coverings. Structure flooding includes basement back-ups. 

Standing Water Greater than One Foot Deep
The next sub-category is standing water greater than one foot in depth. This category impacts the ability of vehicles from traveling safely on the roadway. This is most significant to emergency vehicles but also affects the residents’ ability to leave their home. An additional concern is the ‘wake’ effect created when vehicles try to navigate the deep water. The wakes can exacerbate the impact of the flooding above the level of the standing water.

Street Flooding
The third sub-category is street flooding less than one foot. This sub-category has the least negative impact but still creates a safety issue. As a note, detention facilities on parking lot surfaces are currently allowed to be designed with a maximum depth of one foot.


Evaluating Cost Effectiveness of Improvements

To evaluate the cost effectiveness of any proposed flood control improvement is to establish a value for the property damage prevented by a specific improvement. What could also be factored into a benefit is the value of the “peace of mind” a flood control improvement would provide. For purposes of moving forward, no monetary value will be assigned to this intangible “peace of mind” benefit.

Based on the feedback received after the July 23, 2011 storm event that resulted in flooding throughout areas of the Village, average reported damage in affected single family homes was approximately $8,500 (adjusted to today’s dollars). This average calculation is unscientific since many of the survey respondents did not provide a dollar value, and they survey was not responded to by all property owners who may have experienced structure flooding.

On the cost side of the cost/benefit analysis, the projected improvement costs are relatively easy to estimate. The costs can also be adjusted to be more accurate as time goes on with inflation adjustments. Unfortunately, the benefit calculation is more difficult as was alluded to previously. Every resident will assign a different value for damage, to restoration, and to peace of mind.

In the combined sewered areas where basement backups are the concern, quantifying the number of benefited properties is relatively straight forward, and we believe accurate. For purposes of this analysis, any water in any living unit is considered “structure flooding”.

A bigger challenge is estimating the number of homes/properties used in the cost/benefit calculation for ponding or street flooding problem areas. The reason that this is difficult to estimate is that a definition first had to be established for what level of water on Village streets is acceptable. For street ponding, up to 1 foot of water on pavement is considered acceptable for two reasons.

First, emergency vehicles can cross up to one foot of water with minimal chance of becoming damaged, as 12” near the typical curb height equates to around 9” in the center of the road. Second, our restricted pavement areas in the Combined Sewer Tributary Area (CSTA) are designed to allow up to a maximum of 12” of temporary water ponding on pavements and parking lots. This level is rare and has not been experienced in the CSTA at this depth since July 23, 2011.

Combined Sewered Tributary Area (CSTA)

The CDM Smith report went into great detail analyzing the eight problem areas, proposed improvements for each and the cost per home protected. The report summarizes potential improvements necessary to bring the problem areas within the CSTA up to a 10-year service level of flood protection. The most intense rainfall in the 10-year service level was the 2.1 inches in 1-hour rainfall. The analysis revealed that the current level of service within the problem areas of the CSTA provides protection for basement backups for 1.8” in a 1-hour rain event (with a ± 15% level of accuracy, or 0.3 inches). Outside the problem areas, the system meets the desired service level.

The following paragraphs summarize the various alternatives for all the problem areas in the CSTA. For the basement backup areas, there are relief sewer ‘only’ options and overhead sewer/relief sewer options. For the overland flow problem areas, there is only a relief sewer option.

The ‘relief sewer only’ improvement alternatives consist of the installation of new enlarged local combined sewers to provide additional capacity and diversion connections from enlarged combined sewers to existing sewers to make use of available capacity. Construction of new relief sewers provides the system with additional capacity and the improved level of service. A regional relief sewer provides protection to a determined level of service and all properties tributary to the relief sewer benefit from the improvement. However, larger rainfall events that exceed the Village’s design event could exceed the new relief sewer capacity and still result in basement backups in these and other areas of the Village.

The total estimated cost of the ‘relief sewer only’ alternative is approximately $13 million.

In keeping with the Village Board’s decision in 2001 to fund a cost-sharing program for the installation of overhead sewers within individual private properties, CDM Smith was tasked with investigating the impact of this scenario in the eight basement backup problem areas.

Once the model of the CSTA was developed, CDM Smith evaluated the impact if all affected properties within each problem area installed overhead sewers. Prior to the development of the model, it was not possible to evaluate the effect this would have on adjacent properties. When an overhead sewer improvement is completed on a house, the property increases its flood protection significantly by raising its lowest possible opening several feet (therefore not affected by higher Hydraulic Grade Lines (HGLs). HGL is the engineering term for the pressure and flow depth of water in a sewer.

Development and evaluation of the overhead sewer improvements for each problem area identified that although the overhead sewers provided a more robust way to address basement backups, several of the problem areas still experience high HGLs during the design event. To reduce HGLs during the design events, a relief sewer component was added to the overhead sewer improvements in those problem areas where warranted. Therefore, this alternative is being referred to as the overhead sewer/relief sewer alternative to distinguish it from the ‘relief sewer only’ alternative described earlier.

Because of the impracticality of installing overhead sewers in commercial properties, two of the areas were not evaluated for overhead sewers and only include a relief option for this analysis. The estimated cost of the installation of relief sewers in the overhead sewer/relief sewer alternative is approximately $11 million. This estimated cost for the overhead sewer/relief sewer alternative assumes the Village continues its overhead sewer cost share program with homeowners and therefore the total private component of the cost is not included in the $11 million figure.

If the Village were to fund 100% of the private property overhead sewer improvements, the approximate $11 million cost for this alternative would increase to approximately $15.5 million.

In addition to the eight problem areas in the CSTA with re-occurring basement backups, three additional locations were identified that experienced street ponding that causes structure flooding during intense rain events. It should be noted that these areas were analyzed using the most intense one-hour rainfall event (2.59”) for a 25-year service level. The current design standard for separate storm sewer areas is for 100-year protection, but this is not feasible in a combined system because of the complications posed by the detention of combined sewage and because storage is provided by Metropolitan Water Reclamation District’s Deep Tunnel.

The consultant reviewed potential improvements at the 10-year and the 25-year protection level. Staff determined that providing the 25-year protection level was the lowest level of protection that resulted in passable levels of water on pavements to facilitate emergency vehicle access. Additionally, a number of these areas cannot be controlled by inlet restriction, due to their proximity to State and County owned roadways.

Alternatives for implementation of improvements at the three street ponding locations to provide protection from severe street ponding and structural flooding for the 2.59 inches in 1-hour storm events is estimated to cost $3 million. The $2.7 million cost of the Campbell and Sigwalt area improvements are not included, as these same improvements are provided within the cost of the relief sewer alternative.

Separate Sewered Areas

The Burke Study analyzed the performance of our system in seven areas that have experienced significant overland flooding in the past. According to Village records and resident reports, the flooding in these areas has occurred several times over the last 15 years.

The report summarizes potential improvements necessary to eliminate the excessive flooding within the seven specific problem areas.

The potential improvements for these areas include re-grading, installation of relief sewers, underground or surface detention or some combination thereof.

The relief sewer improvement alternatives consist of the installation of new enlarged local storm sewers to provide additional capacity and diversion connections from these surcharged storm sewers to existing sewers to make use of available capacity. Construction of new relief sewers will provide the system with additional capacity and an improved level of service.

Storm water detention improvements could include surface detention or underground detention vaults. These detention facilities would essentially store storm water until the peak of any storm event passed and then drain or possibly be pumped into the system once capacity is available. The cost for acquiring any easements or land necessary is not included in the estimated costs.


Identifying Key Projects

Listed below are key storm water infrastructure improvements planned for in the 5 year Capital Improvement Program. These projects are part of 17 storm water improvement projects identified by three flood studies performed between 2013 - 2016. The projects will be prioritized based on funding availability and what projects will impact the most residents. Also listed below are the Village’s annual storm water control projects.

Key Projects:

The Cypress Street Detention basin:

These improvements will include an expansion of the Cypress Detention Basin and related storm sewers. According to the flood studies, the lack of a modern storm drainage system in this area results in frequent street and surface flooding problems.

Relief Sewers at Campbell Street/Sigwalt Street/Vail Avenue

This project will involve installation of larger pipes to convey combined sewer water. The lack of adequate drainage in this area results in street and surface flooding that threatens the private residences and businesses in the area.

Improvements in the Greenbrier/ Roanoke Drive-Wilke Road Area

Improvements will include larger storm pipes and more storage to meet current standards. The lack of modern storm drainage in this area results in street and surface flooding that threatens the private residences in the area.

Annual Village Storm Water Control Projects:

Neighborhood Drainage Improvements

This ongoing program provides new or improved access for residents to Village storm sewers. This work done in public right-of-way will help alleviate chronic neighborhood drainage problems directly affecting residents’ homes.

Ongoing Sewer Condition Analysis

The Village is doing an overall assessment of the storm sewer system by televising and analyzing the condition of over 200 miles of storm sewer. This work will be phased in over five years and will identify what areas of the system need rehabilitation and/or replacement work.

Enhanced Sewer Back-up Rebate Program

Beginning in 2018, the Village will contribute 75% to qualifying homeowners who install an overhead sewer system or an approved alternative flood control system. To file an application for this program, click on the quick link  on this page for the Enhanced Sewer Back-up Program. 

To review more information on the status of the Village’s storm water program please view the storm water presentation from August, 2018.