As many of you know, a tailwater is a river or stream whose flow is controlled by a dam, typically in the case of trout tailwaters, a bottom release dam. This means that if the dam needs to be repaired, like the Cannonsville Reservoir Dam on the West Branch of the Delaware River, releases trout rely on for food, water and spawning may be temporarily impeded. This is exactly what happened on last week on the Del. With less than 24 hours notice, the NYCDEP announced on October 4th that the river would receive 0 CFS of releases for several hours on the 6th, and less than 30% of its average flows on the 5th and 7th.
The flow events of last week were done in conjunction with 2 projects, one to repair a leak on a dam release pipe, and the other to calibrate a USGS gauge below the dam. Keep in mind that the usual constant release from the dam is around 150 CFS.
Here’s how last weeks events were supposed to go, according to the Daily Star of Oneonta, NY:
On Monday, Oct. 5, DEP will reduce the downstream flow to 40 cubic feet per second for several hours in the morning while USGS takes readings to calibrate its gage in Stilesville. The release is expected to increase to 150 cfs by noontime.
On Tuesday, Oct. 6, DEP will ramp down the release to zero flow by 5 a.m. The shutdown is necessary for DEP to safely repair a leak on one of the release pipes in the West Delaware Release Chamber, which releases water from the reservoir into the West Branch Delaware River. The shutdown is expected to last the majority of the day. During the shutdown, DEP will also work with USGS to remove debris from around its gage. DEP will ramp back up to 150 cfs when the repair is complete.
On Wednesday, Oct. 7, DEP will again reduce the downstream flow to 40 cfs in the morning while USGS takes additional readings to calibrate its gage in Stilesville. DEP will then ramp back up to 150 cfs.
It’s important to keep in mind that the West Branch of the Delaware is a wide river and at its usual flows, a relatively shallow one. The NYCDEC said they tried their best to coincide with the repairs and dewatering with increased rains and cooler temperatures to protect the tailwater’s precious wild trout and aquatic insect populations. Despite the drastically lower flows happening for just a few hours, the impacts were felt all along the approximately 18-mile tailwater. As you can see in the image above, countless smaller fish who would have been taking shelter in the shallows lost their lives when the waters dropped out below them. But the impact on aquatic insect life is likely what will haunt the fishery for years to come.
To read more about the events, check out this release from the Friends of the Upper Delaware River!