Dark Hollow Dam Doesn't Do The Job

Well, the long-awaited report from the Natural Resources Conservation Service (NRCS) is out for the Neshaminy Creek watershed. The report examines alternatives to lower flood damage in the lower Neshaminy, and speaks to the cost and effectiveness of the alternatives. The Dark Hollow Dam, a project proposed back in the early 60's but never built, has been touted as the end-all and be-all by some. Dam supporters are angry about how NRCS calculated the costs, because the dam was deemed not as cost effective as the "non-structural" alternative, which would move some homes and businesses, and flood-proof others.

And not only is the dam cheaper, they say, the dam is better. One dam proponent was quoted recently (July 17 Bucks County Courier) that with the dam, "100 percent of homes get to participate in flood protection." That's certainly a claim worth examining. To us, that would mean that the dam would have to be the size of Hoover Dam, or have supernatural properties. Lets see how well the dam does in protecting homes from floods, which is what it is supposed to do.

 That doesn't look like "100 percent" participation to us. The dam still allows 76% of homes to suffer some damage, and protects only 2 of seven homes from first floor damage. It's clear that the non-structural alternative provides more widespread protection. Lets look at the numbers with that in mind. Lets see how many homes are actually protected by each alternative.

How about the 100 year flood? This is the flood that each alternative provide protection. NRCS estimates that last year's Hurricane Floyd flood was approximately a 100 year flood

The non-structural alternative protects 74% of the homes, the dam, 31%. That translates to 143 more homes damaged if the dam is built rather than the non-structural alternative. And doing both doesn't do much more. What about first floor damage from a 100 year flood?

Build Dark Hollow Dam and protect less than half the homes (42%) from first floor damage in a 100 year flood. That's hardly 100% flood protection. Implement the non-structural alternative and protect 73% of the homes. With Dark Hollow Dam, fifty-six more homes suffer first floor damage. And adding the dam doesn't add much protection. Dam supporters have been complaining about the way NRCS calculated costs. Okay, put cost aside and look at effectiveness: the dam doesn't cut it.

The fact that adding the construction of the dam to the non-structural alternative doesn't add much more protection hasn't stopped some. Rep. Matt Wright wants both non-structural improvements AND the dam! What a good use of taxpayer funds! It's like taking the bus to work and having a friend drive your car behind the bus, just in case the bus broke done. And doing this every single day.

In addition, it looks like the NRCS report, by using "average annual benefits" to calculate the benefit:cost ratio, underestimates the benefits of the non-structural alternative because the report does not take into account the fact that many more structures are protected by the non-structural alternative than by the dam.

One law worth remembering in this debate is an environmental law dealing with the destruction of wetlands and other disruptions to the aquatic ecosystem. The U.S. Environmental Protection Agency's regulations found in the Code of Federal Regulations has this to say about a project such as Dark Hollow Dam that needs to destroy wetlands:

"...no discharge of dredged or fill material shall be permitted if there is a practicable alternative to the proposed discharge which would have less adverse impact on the aquatic ecosystem, so long as the alternative does not have other significant adverse environmental consequences" (40 CFR 230.10(a)).

The non-structural alternative actually has benefits to the aquatic ecosystem by establishing a small amount of riparian buffer. Given that a wetlands fill permit is unlikely to be issued if Dark Hollow Dam is proposed (and any permit, if issued, is vulnerable to lengthy legal challenges), the non-structural alternative needs to be implemented immediately to provide flood protection to the greatest number of people. Further consideration of Dark Hollow Dam--a dinosaur from the 60s--would conclusively prove that it is nothing but a make-work project, a dinosaur-sized waste of time and money that doesn't do the job. 

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