Stormwater Project: Where are we now?

On the westside of Wilmette, we’re seeing construction wrapping up for Phase 1A/1 of the Neighborhood Storage Project. The construction equipment is gone, signs are stowed, and the dust is settling.

Now that the first phase is almost complete, friends and neighbors have been asking:
What’s the current status of NSP, and what does it mean for my property?

NSP Status by Subbasin

To see how it all fits together, here’s an overview of the westside storm sewer project, with the subbasins color coded to show the three construction phases:

Click for Full-Sized Separate Storm Sewer Area Subbasin Map. (Village of Wilmette, 2020)

Now let’s take a closer look at each phase of construction:

Phase 1A/1 (Completed in 2019-20)

This phase includes a new detention tank at Community Playfields (yellow square), along with new sewer pipes (bold purple and yellow lines), to serve several drainage subbasins (highlighted in purple and yellow).

Since it’s the most complex phase, it’s reassuring that it’s finishing on time and on budget.

Phase 2 (Planned for 2021)

This phase is smaller in scope, with a detention tank at Hibbard Park (red triangle) and new sewer pipes (bold red and purple lines), serving one subbasin (highlighted in light red). Currently, it’s undergoing detailed planning for final review before next year’s construction season.

Phase 2 will also include related upgrades (such as water main relocation), a fix for backyard flooding along Glenview, additional green infrastructure, traffic signal upgrades, and improved drainage for Hibbard Park, which are more economical to manage as part of NSP. (For details, see this village presentation, pp 7-17.)

Phase 3 (Construction in 2022)

The final phase of NSP includes a detention tank at Thornwood Park (green rectangle) and new sewer pipes (bold green lines), to serve multiple subbasins (highlighted in light green and orange).

Detailed plans TBD.

Phases vs Optimization

To fully understand the NSP project, it’s important to know the meaning of Optimization Scenarios.

Originally, NSP was expected to serve only 71 percent of the flood-prone areas on the westside of Wilmette. However, during detailed planning, engineers were able to identify the pockets of flood-prone neighborhoods left out of the project, then group these areas into four Optimization Scenarios, which could be served by adding more tank capacity and storm sewers.

The next map shows Optimization Scenarios 1-4:

Click for Full-Sized PDF of Alternative 3 Optimized (Village of Wilmette, 2019)

For implementation, engineers assigned each Optimization Scenario to the Construction Phase that seemed most appropriate, based on geography and construction constraints, for example, Phase 2 will include Optimization Scenario 1.

So that’s why you may have noticed a confusing mismatch in the scenario and phase numbering systems, and a confusing distinction between associated and optimization storm sewers, as illustrated above.

At this point, the village has approved the increase detention tank capacity required to handle the increase in stormwater volume. During Phase 1A/1, construction included a fully “optimized” detention tank at Community Playfields, as well as “optimization” sewers needed for Scenarios 1 and 3.

The remaining Optimization Scenarios are scheduled for incorporation into the remaining construction phases.

Bonus or Basic Service?

Keep in mind that despite what it sounds like, “optimization” does not really mean “bonus service.” Full “optimization” will be critical for expanding coverage from 71 percent of the underserved westside to 98 percent. And that coverage will simply be standard 10-year storm design protection (along with reductions in flooding for more severe storms).

In other words, full “optimization” of NSP will provide the level of storm protection on the westside that the rest of Wilmette has enjoyed for years, and which is the minimum required for any new development in the US.

When Will It Get Better For Me?

Although your property should experience flood reduction as soon your neighborhood phase is completed, the full benefit across the entire westside storm sewer system will only occur once the entire project is finished.


For detailed plans and timelines for Phase 2, see the Wilmette Village Board Agenda Packet 07-28-20 Stormwater PPT (pp 7-17).

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