Lancaster County - dam removals

[wgmiller]

http://articles.lancasteronline.com/local/4/245830

 

[crs5942]

This sounds problematic. My guess is that they will remove the dams and do nothing else to curb subsequent erosion. Furthermore, it sounds like they are going to create wetlands on top of pseudo-floodplains. Low head dam removals without proper floodplain remediation are not beneficial in almost all circumstances. This does not seem like a scenario where things will done correctly and therefore it will cost millions to deal with the results of these dam removals two decades from now. Too many TU members think that all dam removals are good dam removals. Unfortunately, most groups do not spend enough money to do the removal and subsequent floodplain modification. They need to be moving thousands of tons of dirt once they do these dam removals. Instead, they will throw a few huge bolders on the stream banks and down the road they will wonder why they have erosion problems.

 

[troutbert]

Anybody doing any shad fishing on the Conestoga or Pequea?

Anybody expect significant shad runs on those streams in the future?

As long as Conowingo Dam, Holtwood Dam, and Safe Harbor Dam are on the river, I'm very skeptical about any possiblity of restoration of shad runs on the Susquehanna and tribs. And those dams are used for electric generation so they aren't going anywhere.

 

[billw]

whoa!,

EAch dam removal is different. Stop and check them out after they're removed. The vast majority of these projects result in much improved conditions but it doesn't happen overnight.

Billw

 

[crs5942]

The vast majority of dam removal projects that I have seen result in improvement upstream of the removed dam but have a negative impact on the downstream waterway. This is due to a lack of erosion control, or rather (in most cases) inappropriate stream channel design due to a misguided understanding of natural stream channels in Pennsylvania. Most floodplain "restorations" are done in a pseudo-floodplain that is created by the accumulation of sediment in a reservoir, the removal of the reservoir dam, and the channelizing of reservoir sediments. This is not a natural channel and yet conventional protocol utilizes "Natural Stream Channel Design" to "restore" a reservoir to a condition that never existed previously. The problem is that it cost huge amounts of money to remove the sediments that accumulated in the reservoir and buried the native floodplain by several to tens of feet. Most dam removal sites that I have seen, are very unstable and suffer from significant stream bank erosion because the system did not have naturally occurring banks that were several feet high. Natural stream channel design works well for certain geologic scenarios, including water systems in many western states. It is rarely applicable to Pennsylvania streams, but due to cost factors it is the primary method of floodplain "restoration". Most dam removals in PA create a highly unstable system that has never existed naturally. Remove the dam and remove the reservoir sediments=problem solved. Unfortunately, this is very expensive and most do not want to pay to restore floodplains but rather they want to modify reservoir sediments. Pennsylvania is going to be fined upwards of 15 billion dollars (2012?) if we do not drastically reduce our sediment pollution to the Chesapeake Bay. Instead of paying to do dam removals correctly now, we are going to pay billions of dollars and get nothing in return.

 

[billw]

In a perfect world with lots of $, you are right the best restoration is to remove sediments and restore floodplains. Another alternative is to "step up" the channel through the dam with strategically placed rock arches so that a reconnection to the floodplain (exposed impounded sediment) is provided. The downside is that the original gravel stream substrate is not exposed. To offset this, more wood can be added. This method does keep a lot of sediment in place but it does take some time for the stream to destribute any released sediment.
I have used this appraoch and it does work.

Bill