A Letter from the President
By David G. Barber
Recent flood damage to canals along the Delaware River brings to mind the subject of canal engineering. A problem that exists is that in converting historic canals to parks, we have lost the staff of experienced water managers, both in numbers and experience, and we have changed the use. But, we have not made appropriate changes to the waterways. In fact, inappropriate changes have been made, probably without professional engineering thought.
As examples, consider the Delaware Canal and the Delaware & Raritan Canal feeder. Both of these canals run along the Delaware River, the first on the west bank and the second on the east. While the first received extensive damage in the floods of last fall and in April, the second did not. Why? While I will concede that the D&R feeder only extends half way upstream towards Easton from Trenton, I don't think that is the entire reason.
I think the reason is that over the years of operation, the D&R Feeder was improved in design to take a flood, while the Delaware Canal was not. As you travel along the D&R Feeder, periodically there are, along the towpath edge, long concrete spill weirs that then feed into collector channels and then through multiple culverts through the towpath. Normally, these are dry. But, when the canal water rises a little, a large volume of water can be discharged without human intervention and with reduced chance of the channel being clogged by flood debris. At Prallsville, there is a guard lock. At other points on the canal east of Trenton, there are long, stone paved, lowered spillway sections of towpath that allow flood waters to flow either direction without eroding the towpath bank. This relieves pressures at a predetermined location before the rest of the towpath is overflowed. None of these devices exist on the Delaware Canal.
Recently, on the Delaware Canal, Lock 11 in New Hope was rebuilt to operating condition. The rebuilding project had to endure both floods and much debris was deposited in the lock by flows through it. Originally, Lock 11 had a large basin on its berm side. Water flowing down the canal was fed into the basin just above the lock and discharged from the basin just below. Today, the basin is filled in and used as a parking lot in this tourist town where parking is scarce. But, in rebuilding the lock, no provision was made for a bypass culvert around the lock to replace the original function of the basin. No provision was made at the aqueduct a little upstream or before the canal enters town for spillways to handle floods and there are no guard gates. Thus floods have nowhere to go except through the lock or over the towpath. Similar problems exist elsewhere on the canal.
During the Delaware Canal's operating period, there were lock tenders whose job included reacting to flood waters to protect the canal. While floods still damaged the canal, I'm sure that many were mitigated by the operating personnel. Today, some of this function is done by volunteers who open the manual gates, but I suspect that thoughtful engineering could help. Now, the canal must be repaired from the floods and government is asking for assurances that the damage won't keep happening.
Failure and damage mitigation is part of engineering. Anyone who has an outboard engine knows about this. It is a fact of life that outboard propellers can get wrapped up with weed or rope or hit rock. These events could damage either the prop or the drive train, disabling the craft. However, probably due to bad experiences, the manufacturers put a sheer pin between the prop and the final drive shaft. Thus, if something suddenly blocks the rotation of the prop, the sheer pin fails saving everything else. The boater then raises the lower unit from the water and replaces the sheer pin (you do carry spares ?) and everything is back in service.
Another example of how we have forgotten about this in canals is the Delaware & Hudson Canal feeder at Cuddebackville, NY. At the upstream end of the feeder is the dam with a control structure with vertical gates. The feeder then goes along a hillside to where it used to join into the canal at Lock 51. At the lower end, the original junction was altered at the beginning of the 20th Century to a pool for a hydroelectric station. When the hydro plant was abandoned, the pool's dike was cut through, allowing water from the feeder to flow back into the river and a short branch culvert was installed to connect the feeder to the summit level of the historic canal. The water level in the feeder was maintained by a pile of debris in the mouth of the feeder and by the historic spillway located about halfway along its length. This left a problem of having to cross the water flow at the end of the feeder if you wanted to walk up the feeder to its head.
Several years ago, the county park improved access up the feeder by replacing the debris pile at the feeder exit with a pipe culvert and fill. Water could thus flow down the feeder and walkers could cross the flow easily. The error in this became apparent a few years later when ice flows in the river destroyed the poorly maintained feeder gates and a large amount of water and debris flowed down the feeder. The flood debris clogged the spillway and then the culvert at the end leaving the water no where to go. It therefore overflowed the bank and washed it out leaving two long gaps. The gaps have been filled with new culvert sections, rather than an open canal, but the lack of a relief spillway remains. I hear that the recent Delaware River floods have resulted in further problems.
Similar problems exist along the Chesapeake and Ohio Canal.
I'm all for the reuse of canals as parks. But careful attention needs to be given to protecting the results from flood damage with the greatly reduced staffs of today.
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