ABC Stormwater Flooding Group - Sep 11th, 2018

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Lyons hearing room, town hall. Approximately six attending.

Cambridge Engineer Kathy Watkins gave the evening's first presentation. As a follow-up to the Cambridge's Climate Change Vulnerability Assessment, Cambridge has produced two area-specific documents: the Alewife Preparedness Handbook and Alewife Preparedness Plan. These document's are available from the city's planning department website: http://www.cambridgema.gov/CDD/Projects/Climate/climatechangeresilianceandadaptation.aspx. These documents look at the effects of climate change -- heat, flooding, and sea level rise -- in the Alewife area.

The city expects the number of 90+ degree days to triple by 2030. By 2070 New England will likely have more degree cooling days than degree heating days. Note that these date are +/- 15 years. So 2030 really means 2015--2045 and 2070 means 2055--2085.

Today's 25-year storm will become a ten-year storm in 2070. The Amelia Earhardt dam is expected to remain an effective flood prevention mechanism through 2045. After that, there will be a sigificant chance of storms that overtop or flank the dam.

Cambridge created a FloodViewer application, to aid in visualizing increased risk of flooding. Kathy showed this at the meeting: it was a street level map view, with overlays to show flood elevation. You could see just how close the water would come to your front door. I wasn't able to find this viewer, but I did come across another mapping application, which maps out the 2030 and 2070 100-year flood boundaries. See http://www.cambridgema.gov/Services/FloodMap. Of course, these boundaries are moving targets.

Cambridge's flood boundary work factor into the permitting process for redevelopment of the Lanes and Games site (i.e., the city used their models to determine the 100-year base flood elevation for 2070, and required the developer to build above that elevation).

Cambridge expects a lot of flooding outside the current 100-year FEMA flood boundaries. Much of hurricane Harvey's impacts were outside the FEMA boundaries.

Cambridge is trying to educate homeowners about the risks of flooding, encouraging them to protect their properties. One of their informational brochures is https://www.cambridgema.gov/~/media/Files/publicworksdepartment/Brochures/City-of-Cambridge-Flooding-Brochure_Accessible-Document.pdf. Community resilience as an important part of preparedness planning.

For small residential buildings, Cambridge is asking developers to plan for 10-year storms as projected in 2070, and to prepare for 100-year 2070 storms. This includes conforming to ASCE 24-14 codes for flood resistant buildings. See https://www.fema.gov/media-library/assets/documents/14983.

Changes to building codes will be an important part of future mitigation. However, it's important to give attention to existing buildings, not just new ones.

Green infrastructure does a lot of good in terms of improving water quality, and containing small storm events.

Cambridge's next project will be an assessment of Central Square and the Port. (The Port was formerly known as Area Four -- it's not the same thing as Cambridgeport). The city is planning to construct a large stormwater tank behind the McDonalds in Central Square.

Julie Wormser of MyRWA speaks next. They're starting a project that's focused on coastal resilience and flooding in the Mystic River water shed.

There are 21 cities and towns in the Mystic River Watershed. Mitigation has to be done at a regional level. It's not sufficient to go town by town. Water doesn't care where the municipal boundaries are.

MyRWA formed a collaborative of 10 of these towns, to work on climate reslience. Arlington is a collaborative member. Right now, we're surveying the different communities, to see what they're concerned about.

A lot of communities are concerned about the Amelia Earhardt dam. Petrochemical storage is another concern. This includes all of the jet fuel storage for logan airport, and our LNG tanks. The New England Produce Center (in Chelsea) is another concern, since so much food moves through it.

MyRWA would like to collect municipal stormwater maps from different municipalities, and combine them into a single model. This will make it possible to look at the watershed as a whole.

MyRWA also wants to encourage knowledge transfer. Cambridge and Boston have done significant studies, but not every community has the resources for this. Communities in western MA have even fewer of these resources at their disposal.

Floods will happen, but flooding harm doesn't have to. We've learned a lot about protecting buildings, and we need to learn more about protecting people.