Flood-relief options discussed in Bethany

Members of Bethany Beach’s Flood and Drainage Committee got a more detailed explanation of the options and hurdles involved in reducing flooding problems in the North Pennsylvania Avenue area last week, on the heels of recent news that plans for a pumping system were likely unfeasible.

Alan Kercher and Jack Dolan of Kercher Engineering Inc. (KEI) reported to the committee and others in attendance at a May 19 meeting, with a full presentation of the potential options for dealing with the flooding problem in that area. But, in the end, discussion focused on one option KEI hadn’t specifically presented.

As announced by Chairman and Council Member Harry Steele at the committee’s previous meeting, KEI representatives confirmed that the problems with the proposed pumping system were significant.

The key obstacle to the project is a literal one: the bridge that brings Route 1 over the Loop Canal.

Initially, engineers and town officials had hoped a system of pipes and pumps could move flood waters from the streets to the canal, where they might flow inland and thus reduce the regular flooding in the area.

But the bridge itself is too low to allow full flow of water from the canal westward, locking any additional waters pumped into the canal inside the loop and creating additional flooding problems for properties adjacent to the canal.

“It won’t flood houses, but it will flood yards,” Kercher said.

That option is simply not allowed, legally speaking.

Focus has thus shifted to a gravity-fed system — essentially an upgrade of the existing drainage system in the area, with improvements to drainage pipes and correction of problems with slope and other aspects that have kept it from functioning efficiently.

The new system would use ductile iron pipe – stronger and less likely to fail than existing concrete pipe. Efforts would be made to reduce the impact of corrosion on the iron pipe, with concrete lining and special sleeves to project vulnerable joints.

Kercher said the lifespan of such pipe is usually estimated at 50 years, with wide variations between individual pipes or sections of pipe. The reasons for those variations aren’t entirely predictable, he noted.

The effect of a gravity-fed system would to be handle smaller storms: .25 to .5 inches of rain from a single event — the top estimate for any gravity-fed system, Kercher said. That much water would be removed relatively quickly.

Additional rainfall would still potentially be within the capacity of the system, but those additional amounts would be handled in a more gradual flow through the system and not immediately removed from the area.

Kercher said standing water problems in the area would be reduced, but tidal effects would still be seen. (Tidal flap gates would keep tidal waters out of the system until the tide dropped, then open to release rainwater from the system. The tidal gates would also require increased maintenance to keep them clear of debris.)

He also noted that recent work on drainage at Hollywood Street had been a success due in part to KEI’s emphasis on proper construction, with pipes re-laid three separate times to ensure they were installed at the proper slope.

Beyond the attention to installation and the basic capacity of the system, Kercher said localized regrading would be another focus of the project, targeting ponding problems.

Catch basin grate elevations would be placed above the mean high-tide elevation of the Loop Canal, allowing outflow at mean low tide regardless of the stormwater level in the system, while outflow at high tide would occur when more than .53 inches of water had accumulated inside the system.

KEI defined the gravity system as a “definite enhancement as compared to the existing system” and estimated the cost of the improvement at $1 million.

Despite having pre-stated the major hurdle involved in a large-capacity pumping system for the North Pennsylvania Avenue area, the KEI representatives did elaborate on the various options that were possible if such a system were considered.

Four capacities were addressed, ranging in size from 1,200 gallons-per-minute to 10,000 gallons-per-minute, at costs ranging from $1.5 million to $1.95 million.

Each would involve a “wet well” where waters would collect for pumping by the pumps contained within the well, as well as a likely 10 foot by 12 foot structure for housing electronic controls and other aspects of the system. The structure would likely be located adjacent to the Loop Canal, between First and Second streets.

The largest capacity system KEI labeled as having “significant constructability concerns” with the bottom of the associated wet well to be dug to 25 feet below sea level.

That option would also require significant berming around the Loop Canal, to prevent those pumped-in floodwaters from heading right back out into properties neighboring the canal — a potential permitting nightmare, as well as a likely source of conflict with property owners.

Constructing the largest system would result in a higher mean high tide in the canal — increasing from appoximately 1.4 feet to 2.25 feet, or from 1.7 feet to 2.42 feet at its highest mean level. That would require a berm of approximately 3.5 feet in height around essentially the entire perimeter of the canal, to protect surrounding properties.

An alternative would be to simply leap the obstacle of the Route 1 bridge and allow the desired water flow for the system’s discharge — at a minimum estimated cost of $100,000 to run 700 feet across Route 1, and again a major permitting issue with the state’s transportation and natural resources departments.

(Kercher noted a three-year permitting process was required for a nearby project to correct erosion caused by DelDOT’s own ditches, while Steele pointed to a lack of cooperation from DelDOT in attempts to reduce flooding with work on Hollywood Street.)

Similar, but lesser problems were noted with a 2,500 gallons-per-minute system, with its wet well as deep as 15 feet below sea level. The water level would increase by approximately 4 inches, requiring berming in low spots only, but still raising serious issues of feasibility.

Systems of 1,600 and 1,200 gpm were, in contrast, described as “quite feasible” from constructability and technical perspectives. The smallest system of the four studied was noted as largely identical to the next larger, except in slightly reduced costs due to smaller pumps.

Both could still possibly require localized berming, to be determined by further engineering studies. And both would include a back-up diesel generator to ensure function even when electrical power was out. (Steele emphasized that such a generator would be of a quieter, “hospital” type to minimize noise.)

But the fact that either of the smaller-capacity systems might be considered feasible was a positive note for committee members, who had largely hung hopes for significant improvement on the pumping options — until the physical barrier of the Route 1 bridge had been noted.

Town Manager Cliff Graviet has repeatedly made efforts to hold down expectations for any of the proposed solutions, noting the town’s location just above sea level and the impact of tidal waters on any project. But any way to maximize the storm-handling capacity for such a system has been met with hope.

Those hopes were on full display Friday, May 20, with nearly 4 inches of rain measured over the course of 12 hours and many of the town’s streets blocked off as inaccessible or simply so flooded as to cause drivers to avoid the area.

It was with those kinds of problems in mind that committee members questioned whether there was some flexibility in choosing to build the gravity-fed system.

Though the pumping system idea seemed to have been stymied, could the town possibly choose a plan for the gravity system that might allow them the flexibility to some day take advantage of the additional capacity of a pumping system without rebuilding the entire system?

The core of that hope rests entirely with proposals for an inflatable bladder dam located at the intersection of the Loop Canal and Assawoman Canal.

The most recent hydrological studies of that concept have also been bad news for the town, indicating the project might cause increased flooding in that immediate area beyond even the level indicated by previous studies and making it seem like an increasingly distant possibility.

Certainly, holding off on the North Pennsylvania Avenue project until a final determination of the dam’s feasibility could be made was an idea that was quickly rejected, with such a date in the distant future.

Indeed, Steele said the project was one he planned on leaving in the hands of his grandchildren — noting pointedly that he does not currently have any children, let alone grandchildren. Thus, even the idea’s greatest proponent has acknowledged it might never happen at all.

But, if it were to become reality some day in the future, the bladder dam would inherently provide a solution to the Route 1 bridge problem in the North Pennsylvania Avenue project. The dam would lower the water level of the entire Loop Canal, allowing the drainage that is currently not possible thanks to the bridge.

That would mean no increase in flooding around the canal due to the pumping system and thus reopen the possibility of even the larger-capacity pump system, without the need for berms and related permits.

It may be the equivalent of a pot of gold at the end of a rainbow, but committee members deemed the possibility worthy of at least some number-crunching. So Kercher said he would prepare additional costs and facts related to a hybrid system. Dolan ball-parked the increase in costs at “a couple hundred thousands dollars,” with a more realistic estimate to come.

Such a system would use larger-capacity pipes, in preparation for a possible pumping system. That would also leave more standing water in the system — a fact that was largely put into the plus column for the idea, as it would add holding capacity to the gravity system.

If the pump system were to be added later, it would require reconstruction of only 50 feet of pipe, Kercher said.

Kercher also assured Public Works Supervisor Brett Warner that the hybrid system could be constructed without significant additional maintenance needs. That put Warner on board for the idea. “If it can be done, I’m completely in favor of a larger system that we can add onto in the future,” he said.

Steele said he also preferred that the town plan ahead, noting that the additional standing water in such a system would only be an expansion of the standing water to be expected in any gravity-fed system at any point in time.

Graviet noted that the estimated cost of a hybrid system (perhaps $1.3 million) was similar to the pumping systems ($1.5 million) and warned against the potential for increased expectations of the end result due to the increased costs. He also cautioned that “nothing we do will address a tidal event” — the most common type of flooding problem in the town.

Kercher also voiced a note of caution, saying that if the dam were only “a pipe dream” the town should not go with the hybrid gravity system but with the original concept for a basic gravity system. Steele seconded that caution, telling committee members not to plan for the dam in making their decision.

Warner advised caution in the other direction, however, saying that if the town didn’t consider the possibility of the dam, it could end up in place and the town would have to reconstruct the entire system.

Committee members voted unanimously to ask KEI to provide a realistic cost estimate for the hybrid option, which could then be considered by the town council.

Graviet noted that $500,000 is currently queued up in the town coffers for work on the North Pennsylvania Avenue project, with some time sensitivity for fiscal decisions related to the project.

The gravity-fed system concept was nearly ready to go out for bids as of the May 19 meeting, and the delay of modifying the package to include a hybrid option was described as minimal.

Also at the May 19 meeting:

• Committee members voted unanimously to have KEI do further analysis on hydrological data regarding the impact of the proposed bladder dam.

Previous engineer Tim Ruga left his data with KEI for further work and analysis, but KEI’s preliminary examination had resulted in differing opinions on the potential impact of the dam. Those differences were categorized as potentially ones of differing approaches and interpretation of the data, but KEI’s first look indicated a larger impact on properties near the dam location.

Steele said the town was not at a point to consider abandoning the bladder dam concept, while Graviet said he felt the town had invested enough in the dam concept that it would be “foolish” not to investigate, do additional research and obtain an opinion that could put the issue to rest one way or the other.