Q&A
Inland flooding risk assessment and mapping for basement ADU safety
0:51:01
·
5 min
Council Member Pierina Sanchez inquires about how inland flood risk should be assessed for basement ADU safety and how risk mapping will be updated over time. Kim Darga from HPD explains the city's approach to flood risk assessment, mitigation strategies, and plans for creating and maintaining flood risk maps.
- The city has developed a better understanding of inland flooding risk since Hurricane Ida
- Basement or cellar legalization will not be allowed in coastal flood areas or high-risk inland flooding areas (10-year rainfall flood risk)
- The city will publish flood risk maps within 120 days of the legislation's enactment and update them every 5 years
- Various mitigation measures are being considered for areas with less acute flood risk
Pierina Sanchez
0:51:01
Inland flooding.
0:51:02
So notably, this legislation creates geographic exclusions for basement and seller ADUs in inland flooding at, areas as as you've just mentioned, deputy commissioner.
0:51:11
How does the administration believe that inland flood risk should be assessed for the purposes of basement ADU safety.
0:51:17
How should this risk mapping be updated over time to reflect the changing climate?
Kim Darga
0:51:24
Sure.
0:51:24
So as I mentioned a few minutes ago, when we originally, created a a basement seller conversion code back in 2018, 2019.
0:51:36
We were primarily concerned with coastal flood risk.
0:51:39
That was after Sandy.
0:51:40
We understand we understood the impact that storm surge could have in terms of safety.
0:51:46
We hadn't really thought as much, I think, in terms of basement, especially subgrade unit, subgrade units, the potential risk of inland flooding.
0:52:00
And, since Ida, we have done substantial work in better understanding trying to better understand that risk.
0:52:08
We have looked at, basement flood mitigation.
0:52:12
We have a study that is ongoing that we expect to have the results of by, 2027.
0:52:18
We've looked at, the feasibility of backwater valves in terms of mitigation for inland flooding.
0:52:26
And our and, DEP has actively looked at, geography where there is higher, likeliness of severe inland flood risk.
0:52:39
And so the, the legislation that you have before you today, particularly with regard to, basement and sellers, does not pro does not allow basement or seller legalization in coastal flood areas or in areas where there is acute or high risk of inland flooding.
0:53:03
And that is specifically the 10 year rainfall flood risk area, which is approximately 2 inches per hour.
0:53:10
And, we do expect that there will be some allowance.
0:53:16
We're DOB is working we're gonna be working with DOB and the other agencies over the next couple of months, if this legislation is passed to create rules around areas that have less acute inland flood risk, but where additional flood mitigation actually may be warranted.
0:53:34
And, there are a range of strategies to mitigate risk, including raising, you know, utilities, making sure that windows, are raised a little bit, so not right at grade, thinking about where, water moving away from the building rather than toward the building.
0:53:54
So some pumps, there are a range of mitigation measures that could be adopted, so that we potentially could allow legalization.
0:54:02
Right?
0:54:02
Because we know that a lot of folks are leaving in these homes today, clearly not safely.
0:54:10
But making sure that there's additional measures in place.
0:54:13
We have thought about flood risk more generally for ADUs.
0:54:19
So for, at grade, above grade ADUs, there are you could elevate depending on your coastal or inland flooding area.
0:54:28
I think that is unacceptable approach.
0:54:32
More generally, we are looking at having, flood or water, sensors, in homes, for, participants in the basement pilot program, the temporary amnesty program, not only will they be required to install those, water sensors, but also to, post, emergency information for the resident and enroll and notify NYC, which, has notifications around flood risk for residents.
0:55:06
So there's a number of other measures that we have written into the code to make sure that there are both warnings, but also that flood risk is managed.
0:55:17
I know you also asked about geography.
0:55:20
We are planning, to have, the maps, available within a 120 days of the legislation's passage.
Pierina Sanchez
0:55:32
I'd like to acknowledge that we've been joined by council member Dinowitz, and that was actually, I have a clarifying question on that.
0:55:39
So for the 10 year flood risk rainfall, is that for the rainfall area, is that a map that is gonna be created and maintained by the city, city agency, or is that a FEMA
Kim Darga
0:55:51
So that will be a map that we will publish within a 120 days of enactment.
Pierina Sanchez
0:56:01
Okay.
0:56:01
And how often, at this time are are
Kim Darga
0:56:04
are the agency consent?
0:56:06
Update it every 5 years thereafter.
0:56:08
We do expect that flood risk will change over time and potentially get worse and so we wanna make sure that those maps stay up to date.
Pierina Sanchez
0:56:18
You see you said the city will publish the map within a 180 days?
Kim Darga
0:56:22
100 and I believe a 120 days of enactment.
0:56:26
Great.
0:56:27
Thank you.
