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September 2021

Flooding and the Village of Mamaroneck
Part I
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With great compassion for those affected by the recent flood and gratitude to the emergency responders and others who have worked tirelessly to help survivors,The Mamaroneck Project is providing this article to encourage further discussion regarding what the Village can do to mitigate flooding and its disastrous impact. (In the interest of brevity this article does not address flooding caused by coastal storms and Long Island Sound.)

Flooding poses substantial risk to life and property in approximately 750 homes and businesses located in the floodplain of the Village of Mamaroneck. And when emergency vehicles can’t get through major roadways such as Mamaroneck Avenue or the Boston Post Road due to flooding, the entire Village is vulnerable.

 

Observing the widespread flooding across the Northeast resulting from tropical storm Ida, it’s clear that it’s impossible to completely control or predict floods. But as certain areas of the Village repeatedly find themselves underwater we ask - what can the Village do to mitigate recurring flooding events?

We must accept the fact that the Village will be increasingly vulnerable to significant flooding events due to accelerating climate change whether or not the Army Corps Plan designed for the Village is implemented. As our hardworking Village staff and first responders continue to assist in the massive tropical storm Ida recovery effort, we look to our elected officials to enact immediate flood mitigation improvements and institute stricter construction and maintenance requirements for properties in the floodplain without delay.

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Why is the Village Prone to Flooding?
It's Our Topography - 

  • Much of the Village is in low-lying areas (close to sea level)

  • The Village is located at the bottom of multiple watersheds and storm water naturally flows down from upper Westchester County.

  • It includes two relatively narrow rivers – the Mamaroneck and the Sheldrake – that are prone to overflow their banks in big storms which converge in Columbus Park.

  • A large area of the Village sits on top of an underground, 250-acre reserve of water called an ‘aquifer’ which can produce groundwater flooding. The Mamaroneck aquifer stretches roughly from Fenimore Road to West Street in Harrison.

 

As a result, in torrential rainstorms, flood waters may flow both above ground from overflowing rivers and stormwater runoff AND rise up from underground as the water volume exceeds what the aquifer can contain below the surface.  

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It’s What We’ve Done -

  • Insufficient flood mitigation building standards in the Zoning Code - Standards are based on old data and guidelines and should be updated for accelerated climate change results.

  • The addition of fill to heighten the entire site of new construction projects causing a “hill” effect which can push water into lower lying areas. What happens on one construction site impacts neighboring sites in a significant rain event.  Science tells us that water flows downhill and those at the bottom will be flooded.

  • Building development in the floodplain (as more surfaces are covered with buildings or asphalt, less water can be directly absorbed into the ground) and on top of the aquifer where they are frequently vulnerable to groundwater flooding.

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Excerpt from FEMA document "Regulating Within a Floodplain" produced for Ward County in North Dakota. Read more to understand the difference between a floodplain and a floodway.

The Army Corps Plan
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Many officials cite The Army Corps of Engineers plan as the answer for flood mitigation in the Village. Many ask why it hasn’t been implemented yet, without fully understanding what it can – and can’t – do. Let’s look at some aspects of the Army Corps’ most recent iteration of the plan which was proposed in 2017 and named Alternate 1Z - Link to report describing plan.

 

  • The total projected cost of the plan has been updated to $88 million for FYI 2021. The Village is responsible for paying 25% or roughly $22 million (cash and in-kind service). An Independent External Peer Review Report prepared by Battelle for the Army Corps states that the budgeted costs for the plan may be seriously underestimated.

  • Despite its large price tag, no engineering expert has gone on record to state that this plan will solve the Village’s flooding problems. The Army Corp’s original estimate for how many homes will be helped should be re-evaluated in the light of climate change. 

  • The Army Corps plan calls for “channelizing” the Sheldrake and Mamaroneck rivers with concrete retaining walls in certain areas to deepen and widen the rivers. Channelizing a river is an effort to control water movement by building concrete walls which then help to move the water more quickly out of the area – so water would be pushed faster into the Columbus Park area where the two rivers converge.  There are also public safety concerns voiced by Battelle if anyone were to fall into the channel.

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Example of an Army Corps concrete retaining wall for channeling a river

  • The plan only addresses river flooding, it would have no impact on reducing groundwater aquifer flooding.

  • The plan is expected to require 14 acres of permanent property easements from 88 private landowners; private property could be taken from landowners through eminent domain.  Additional property would be needed on a temporary basis to stage the project. Landowners would be paid for permanent or temporary use of their property based on a negotiated amount, with the cost of legal representation in negotiations borne by individual property owners.

  • The U.S. Fish & Wildlife Report of August 2015 states that the proposed project “will adversely affect riverine, palustrine, and terrestrial ecosystems of the Sheldrake and Mamaroneck Rivers…”; and up to 200 mature trees will be removed along the riverbanks. It is possible to mitigate some of these adverse findings through changes to the plan.

 

As the “cost-benefit ratio” required for federal projects to be approved is razor thin, is it realistic to think the plan will ever be approved?  And even if it is, how much of a difference will it make to flooding in our Village with the accelerated impact of climate change?

Tom Murphy on LMCTV 2017 - not all areas of the Village are covered by the Army Corps Plan

If the Village is prepared to spend over $20 million towards mitigating the impact of flooding, it needs to determine if paying for the Army Corps Plan is the best use of those funds. Perhaps aiding property owners to raise their homes or undertake other flood proofing measures would put that money to better use.

 

Rather than simply wait and hope that the Army Corps Plan is implemented, it makes sense to consider alternative plans and common-sense suggestions the Village could take RIGHT NOW to help alleviate the suffering of residents.

The Mamaroneck Project Point of View
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Suggestions for Improved Emergency Planning -

  • Issue earlier flood warnings based on weather forecasts and common sense to give residents more time to make evacuation plans and move portable valuables to safe locations.

  • Identify several areas in the Village where residents of low-lying areas may park their cars ahead of the storm and provide transportation back to their homes or to a shelter. Clearly communicate the existence of these areas to those living in the floodplain.

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  • Set up evacuation sites early (at Mamaroneck High School and other locations).

  • Provide flood inflatable barriers and/or portable flood gates to locations where they would be helpful.

  • Establish a reverse 911 message service to get the word out to residents living in the floodplain.

  • Explore additional emergency plans and communication to residents.

  • More fully engage the Flood Mitigation Advisory Committee and other interested homeowners to explore other options

 

Suggestions for Long-term Mitigation Planning -

 

  • Ensure that catch basins are cleaned on a regular basis.

  • Re-institute river clean-up days when volunteers can help remove debris from Village rivers.

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  • Tighten enforcement of stormwater management plans for new and re-developments. Institute fines for stormwater management plan violations and use the money collected as a relief fund for residents impacted by flooding.

  • Stop passing zoning laws that encourage residential development in the floodplain and review the Transit Overlay District zoning in the Washingtonville neighborhood.

  • Pass legislation banning basement apartments in the floodplain and develop solutions to increase affordable housing stock in other areas of the Village. There is a social injustice when the vast majority of affordable housing available in the Village is located in the areas very likely to experience significant flooding.

  • Revise zoning requirements for new construction to include improved flood mitigation measures in the floodplain and immediate surrounding areas - including sufficient setbacks for construction and parking lots along riverbanks and other bodies of water. Thankfully, the Board of Trustees did not pass the 2020 proposed legislation to decrease the 50-foot required set back from rivers, streams and other waterbodies.

  • Engage a firm to explore the location of the aquifer and its impacts on flooding.

  • Incentivize property owners to bring their properties into FEMA compliance. Investigate grants for raising homes in the floodplain above base flood level. Many structures predate current FEMA guidelines for floodplains, with some buildings actually situated within the floodway itself. Read more about the importance of keeping floodways clear.

  • Establish a revolving fund where low-interest loans could be made available to help residents floodproof, raise their homes, etc. Advise property owners on solutions for hanging water tanks and boilers horizontally so they are off the ground.

Consider an Alternative to the Army Corps Plan -

The Village could consider investigating other solutions such as the  Hydroquest Report prepared by hydrologist Paul Rubin. The Hydroquest Report proposes a different and much cheaper strategy that seems worthwhile for the Village to explore.  While the Army Corps Plan focuses on structural engineering methods of controlling floodwaters, the Rubin Report claims these are outdated and less effective methods than what “…modern fluvial geomorphic concepts that protect water quality, ecosystem health, recreational opportunities, aesthetics and values.”

As stated in the March 24, 2008, report by former Village Engineer Keith Furey there are no “quick-fix” answers to flooding and flood mitigation must be an ongoing process.  It’s clear that no flood mitigation plan will be 100% effective – there will always be some flooding. But the Village should not simply sit on its hands as it waits for the maybe-never-to-be-realized, and insufficient Army Corps Plan, and instead seek ways immediately to make flooding less devastating.

You can send the Mayor and the Board of Trustees your concerns and questions regarding flood mitigation at