In a quest to do for claims against the city what Crime Stat did for crime, Scott Stringer recently released ClaimStat. It maps out claims against the city, including the date of occurrence, type of claim, location and amount paid out in the claim.

It’s a great step for transparency, but once again the city failed to release the data in a machine readable format. But fear not: the amazing Chris Whong (of Taxi Visualization fame and an organizer of BetaNYC, NYC’s network of civic-minded hackers who are opening government data) posted a quick how to on extracting data files from the maps. So with that, I was off and running.

Today’s post is on Sewer Overflow Claims. What are Sewer Overflow Claims you ask? Well, the city’s network of sewers can only handle so much water at once. During large storm events, they can overflow and back up onto city streets or they can occasionally get clogged for other reasons. When the sewers do overflow, the water can cause damage to property and thus property owners can file a claim against the city for that damage. The good news in all of this is that the claims data can help us identify where flooding from sewer overflow is happening the most. If we can identify the worst offenders, the DEP can better target infrastructure projects.

First some quick stats. In the two years present in the data, there were 1,168 claims filed. The bulk of the claims were in Brooklyn and Staten Island:

The average payout for those claims which have been paid is around $4,000.

Scott Stringer’s ClaimStat report explores flooding by Community District. I decided to take a more detailed look at the underlying neighborhood data given that Community Districts span many neighborhoods. So I split the data into Neighborhood Tabulation Areas (NTAs), which are neighborhood designations used by the Department of City Planning for population projections. I then counted the number of claims filed in each area over the two year period to get a view of which neighborhoods experience the most flooding:

The results show that Canarsie fairs worst, with 16% of all claims. But second behind it is the Bergen Beach NTA, which is adjacent to Canarsie in Brooklyn, and third is the Sheepshead Bay NTA, which is just south of that. These three contiguous NTA’s make up almost a third of all Sewer Overflow Claims in the city. The top 10 neighborhood areas on the list made up half of all claims, making these prime areas to reinvest in new infrastructure.

To get a different view, I created a heat map, or should I say a wet-map, of all the claims in the city:

The map clearly identifies hot- errr I mean wet-spots to focus on as far as mitigating these issues.

I was also curious to see how consistently the flooding hits the same neighborhoods. So I chose the three largest storms in the data: Hurricane Irene, Hurricane Sandy, and a record breaking rainstorm that hit the city a few weeks before Hurricane Irene.

I mapped out the claims for each storm below, as well as all the remaining claims that were not one of the three storms.

Interestingly, although there is some overlap, there are also distinct areas affected by each storm. To look at it another way, we can break those same three storms down in a table to see their individual effects on the neighborhoods with the most claims:

Only Canarsie and the Bergen Beach NTA were hit severely by all three storms. The other top flooding neighborhoods seem to be storm-dependent.

One more way to look at the severity of flooding is to explore the number of unique days in that claims occurred, e.g. if 10 claims were filed in one day it would still only count as one in this metric.

Once again, Canarsie tops the list. Sewer overflows that resulted in claims happen about every 5 weeks on average there. But the next five NTAs are in Staten Island according to this measure.

So the conclusions? Well Canarsie, Canarsie, Canarsie for one. It appeared on the top of the list no matter how I sliced it. It’s pretty clear that the sewer infrastructure needs upgrading there and I hope the DEP has it on the top of its list as it is by far the area with the most flooding claims. Other than that, several neighborhoods seem to vie for second place depending on what measure you use. Neighborhoods in South East Brooklyn, as well as many along the water in Staten Island seem like good contenders.

It’s important to note that while increased claims indicate increased flooding, its not necessarily true that increased flooding will create increased claims in all affected neighborhoods . One could imagine that there might be information gaps around this issue, leading some neighborhoods to be undercounted in these numbers. Also, there is flooding not attributed to sewer overflow. So as always, this data should not be looked at in isolation.

And finally a closing thought: reducing the number of claims against the city can only be a good thing. No one wants our fine city to end up under water.

Neighborhood Tabulation Area Data here.

Claims data here with extraction instructions here.

Maps made in QGIS with Open Layers Plugin for Google Maps, Raster Plugin for Heat Map.

Charts made in Excel.