Preparedness

Is Dredging a Solution to Flooding Problems?

Poorly devised, randomly executed or under-engineered dredging, deepening or widening of streams has proven to be ineffective in preventing subsequent flooding.

by Vicki Terwilliger, Republican & Herald, Pottsville, Pa. / August 19, 2018

(TNS) - As communities wrangle with flooding across Schuylkill County, Pa.,some ask why dredging waterways is not considered a solution to long-term flood abatement.

The state Department of Environmental Protection and some environmental leaders say other techniques are preferred.

DEP defines dredging as “the removal of sand, gravel, mud or other materials from the beds of regulated waters of this Commonwealth, in accordance with Chapter 105 of the PA Code.”

“The DEP permits projects that involve dredging for stream restoration, emergency stream stabilization — like flooding — and beneficial use of dredged material,” said Colleen Connolly, DEP community relations coordinator for the Northeast Regional Office, Wilkes-Barre. Each scenario is project specific and viewed on a case-by-case basis, she said.

Historically, there’s been an evolution on the response, according to one local contractor. When Hurricane Agnes flooding damaged the area in 1972, Ron Aungst was in Swatara Creek in Pine Grove with his excavating equipment.

“At that time, we went in the stream. Times were different. We were told we could go into the creek. We pushed the silt out on top of the banks and didn’t haul it away,” Aungst, current president of Arthur “Pat” Aungst Inc., Pine Grove, said.

Crews dredged from Ravine to Route 645, within the borough and Pine Grove Township, he said.

“That was the practice back then,” he said. “The stream looked wider than it does today. The stream bed was deeper, and it was quite an open channel when we were finished.”

Work a few years later included adding riprap (larger rocks) along the embankments in a coordinated effort with the Schuylkill Conservation District, Aungst said.

Since then, the company has worked on Swatara Creek four or five times, he said, at the direction of the DEP and the U.S. Army Corps of Engineers. The last time was following the 2011 Tropical Storm Lee flooding.

More recently, excavating crews were able to remove sand bars in waterways within 6 inches of the height of the water level, Aungst said.

Aungst’s company has been involved in dredging in other areas of the county. They conducted dredging in Port Carbon but weren’t involved with a bridge collapsed there, which happened after another company came in, Aungst said. They’ve also completed dredging in Pine Grove Township to the Lebanon County line, and dredged in Shenandoah in 1975 and 1976. Other water control projects they’ve conducted were installing riprap in the Pitman Valley with the county conservation district and creating a flood plain in Schuylkill Haven.

“Dredging was conducted many years ago (Agnes 1972). This was before our current regulations were in place. The method was to put a bulldozer into the river or stream channel and push the material to the sides of the streams. This method is not recommended and potentially very dangerous to many landowners up and downstream,” William Reichert, Upper Swatara flood recovery manager, Schuylkill Conservation District, said.

Misconception

Connolly said she’s unaware of any change in opinion on DEP’s part about using dredging to solve repeated flooding events, and she knows of no changes to DEP permits in regard to the method. However, she said there has been a common misconception that dredging a channel or stream deeper and wider than it was prior to the last flooding event will create even more capacity for water to flow during storm or flooding events.

“Poorly devised, randomly executed or under-engineered dredging, deepening or widening of streams has proven to be ineffective in preventing subsequent flooding,” she said. “All streams transport sediment during storm events and under-engineered dredging, deepening or widening of streams reduces the stream’s capacity to effectively transport normal sediment loads. This leads to rapid sediment deposition in the channel, as well as instability, increased stream bank erosion and damage to aquatic environments,” Connolly said.

Dredging, and possibly creating a levee system, have been among the brainstorming ideas mulled at Pine Grove Borough Council meetings. Both Pine Grove and Tremont have inquired about dredging in the past, according to Connolly.

However, DEP has not received any project proposal or permit application from those boroughs, she said.

Open drainage pipes


Tom Fickinger, Pine Grove Borough Council vice president and a member of the borough’s Flood Mitigation Committee, said that the borough would be receiving an emergency permit from DEP to clear away parts of the Swatara Creek where drainage pipes have become blocked with mud and silt. The council on Aug. 1 approved Aungst to do the pipe-clearing work at a cost not to exceed $50,000. Fickinger said the effort may also be used as a future training mission for the Pennsylvania Army National Guard from Fort Indiantown Gap.

“The borough has indicated dredging may be necessary to open stormwater drainage pipes,” Reichert said. “That may be true, I do not know enough about their stormwater system to address that issue. It does appear that there was a problem with water backing up in the stormwater pipes. Tom Fickinger suggests most of the damage was a result of that issue. Continued maintenance of stormwater pipes is always a problem and concern of communities.”

Up and downstream

“I have not changed my opinion of dredging to reduce flooding,” Reichert said. “Dredging does not prevent future flooding issues and can be detrimental to upstream and downstream landowners. Dredging of a stream or waterway should not be undertaken lightly. A plan would need to be developed looking at many factors. Considering the amount of dredging necessary to achieve even minimal lowering of potential flood events makes it impractical since sediment continues to come downstream and will settle out where you remove material requiring constant maintenance.”

Dredging is routinely used in navigation channels and around ports in places like Philadelphia and New York, according to Reichert. Dredging can also be useful to remove sandbars and for debris removal around bridges and culverts, he said.

“The Northeast Regional Office here in Wilkes-Barre is not aware of any large-scale dredging projects that have been completed. Most dredging projects in this region that were authorized by DEP have been gravel bar removal and stream maintenance at bridges and culverts,” Connolly said.

Restore, stabilize

There are improved methods for flood control, Reichert said.

“We advocate for wetland restoration/enhancement and streambank stabilization and buffer zones to reduce sedimentation. Finding better ways to handle stormwater run-off is something all communities can and should be doing. I have seen some literature that states for every $1 spent on pre-mitigation, $6 in post-mitigation will be saved,” Reichert said.

In June, it was announced that Pine Grove would receive a $3 million grant from the Department of Community and Economic Development and $2.9 million from DEP for flood mitigation efforts and floodplain restoration development. The county plans to use $4.5 million — $3 million of the Community Development Block Grant-Disaster Recovery money and $1.5 million in Growing Greener cash — to clear debris from the Swatara Creek and provide a place for excess water to go, County Administrator Gary R. Bender said.

Floodwalls

The possibility of building floodwalls within Pine Grove was evaluated along with six scenarios on how best to try to reduce flooding there, according to Reichert.

“Floodwalls were not only very expensive, requiring a lot of cooperation from landowners allowing for building of the structure (i.e. giving up land for the wall), and the structures would have created more problems for landowners upstream and downstream. By permit — any material that would be dredged out of the creek would need to be removed from the floodplain and not only could not be used for floodwalls, it would be unstable material and thereby unsuitable. Remember, it is sediment that eroded and ended up in the stream and will erode again,” Reichert said.

Engineering studies would be required to determine the feasibility of building a dike or levee system, according to Connolly. Dikes or levees are generally engineered structures. Therefore, it is unlikely that dredged material would be suitable for use in their construction, she said.

Contact the writer: ; 570-628-6007

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