Thursday, October 6, 2016

Experts brainstorm resilience in Ellicott City

On the same day Main Street finally reopens after the catastrophic flood on July 30 of this year the Department of Planning invited a panel of planners, engineers and stormwater experts to brainstorm ideas for how to plan against future floods.

With the major repairs complete but no plans for a real solution adopted, the Planning Director and his Deputy of Howard County's DPZ resorted to inviting an assortment of experts with some ties to the area to come in for free and participate in a brainstorming session.

The valleys and streams of Ellicott City
Some twenty landscape architects, architects, planners, engineers, and water experts followed the call and conducted a wide ranging discussion trying to rein in the fluid topic.

"What are your objectives" was the first thing somebody wanted to know. The department members punted and said a set of objectives will be developed later. However, they offered a list of "buckets" that kind of reveal the goals:

  • Economy, 
  • Rebuilding, 
  • Preservation, 
  • Environment. 

This is a telling list, even if one doesn't take the order as a  hierarchy of importance. Clearly, any drastic proposals that include abandoning the bottom of Main Street or disturbing its historic character through any type of fortification are out of the question. Not that I think one should consider abandonment or demolition seriously, but if one invites a bunch of experts, it would be kind of interesting to see if anybody would have suggested it. Besides, it isn't an issue of full abandonment or full preservation. Any of those greenway measures taken in other places like Boulder Colorado or Frederick, Maryland require allowing water to expand somewhere, where it doesn't do damage. Any such area is currently elusive in Ellicitt City, unless one allows drastic land use changes and some changes to the historic downtown.

There was general agreement that 6" of rain in two hours are not manageable without flooding, given the topography and specific conditions of Ellicott City with its three-tributary four-valley configuration leading into an ever narrower channel leading perpendicularly into the Pataspso which is running in a deeply cut valley at that point.

It also became apparent that all suggestions that dealt with the engineering and management of water fell into the two main categories of detention (keeping the water stored) and conveyance (controlling the flow of the water that isn't retained).
Extreme scouring due to high velocity
One participant, interestingly a hydrologist, steered towards a set of questions that were less centered on engineering water. "Manage the people and things that are affected by water",  he demanded. How to warn and evacuate people, how to protect assets so there is less damage from water, how to discuss cost and benefit? "Who carries the cost, who has the benefit", he asked.

He also made very sensible suggestions about how cost can be reduced for the shopkeepers downtown: Could they form a special group and shop for flood insurance as a more powerful collective, presumably getting a better rate than a bunch of individuals? Could shopkeepers rent a joint storage facility so they wouldn't need to store their inventory in the basements below the store where they get destroyed even in smaller floods. Good questions, all. One could easily see how the businesses as a group would get much further than in the current condition of individuals on their own. Splits and tension have already become visible between those who stay and rebuild and those who sell, for example.

Another set of issues, less engineering and more policy, revolve around why current rules and regulations aren't strictly adhered to and whether the County follows best practices on its own properties. The very large parking lot in front of the County government and courthouse high above downtown is a perfect example: With electric car charging stations and a slew of small bio-retention areas the answer looks like, yes. But the truth is that these lots, which are part of the Hudson watershed, have no stormwater management component that deals with water quantity beyond the first inch of rain. The little landscape islands into which the parking lot water runs are designed to improve the quality of the initial most polluted rainwater running off the asphalt. The goal there is water quality, not retention. For Ellicott City, though, this isn't an alternative. Its a must on both counts.

In recognition of that fact, current stormwater regulations in place for this area already require ("shall have") 100 year storm water facilities.  But according to David Woessner of Bohler Engineering in Towson a local survey conducted by him shows only less than a handful of such "100 year ponds". He says almost all facilities are only designed for two or ten year storms. Over half of the developments, Woessner estimated, have no stormwater management at all. Around 440 acres in all, Woessner said.

Somebody else added, that even the few 100 year facilities would still have inlets and pipes that can convey only two or ten year storms. In other words, their large retention holding capacity doesn't even come to bear in a heavy rainfall, because the water can't be conveyed into the holding area or pond. "These things have been known for years, this could be changed right now, but it isn't been done" one participant told me afterwards. "They are out there fixing those damaged facilities, all they have to do is lift the weirs (the overflow elevation) by a foot so they hold more water, but that is not what they are told to do".

The matter of policies comes down to enforcement it seems and to the tough question of retrofits. How to force developments without management to add stormwater facilities? "You should focus on strategic retrofits" a participant admonished, "not across the board, for cost reasons". Others admonished to design retention facilities with staggered discharge, so they don't overflow all at the same time. "For a better hydrograph", the hydrologist clarified. The question if any new development should be allowed in a watershed that is already 90% or so developed is also a matter of policy and political will.

There is also the issue of what the Maryland Department of the Environment will allow. As stormwater management techniques evolved over recent decades, the traditional priority on conveyance (concrete channels) has taken a backseat to water quality and environmental concerns to protect the streams, the stream-banks, the Chesapeake Bay. So called "in-stream facilities" such as weirs or dams have been frowned upon, because of their negative impacts to streams. In fact, dams are actively being removed in the Patapsco right now. But what if those in-stream installations wouldn't retain water at all times, "if they let two and ten year floods go but dam the 100 year flood?' somebody asked and someone else distributed the template of an engineering drawing showing such a solution.

In the end, some "heroic" large-scale expensive water retention facilities will have to be built even if it may not be the subway size underground flood tunnel under Main Street. Large retention basins under the two expansive remote parking lots at the top of Main Street, for example, would take a good amount of water and hold it before the the final run alongside Main Street and under buildings.

Even short of gigantic underground holding tanks these parking lots should get the attention. They cause large amounts of water run-off to simply go straight into the streams. Simple storage through pervious pavement placed above rock-layers or storage pipes could prevent a good amount or all of runnoff  they cause. Any measure on those public lots would meet all the items on the bucket list without any compromise on economy, the environment or preservation. Green open space is definitely in short supply in downtown. Maybe the two parking lots should become open holding lakes that can grow and shrink. Waterparks as amenities, facilities that combine the quantity with the quality aspect.

Of course, these lots are too far down the watershed to be effective by themselves. Further upstream, bigger ponds and better retention will be most effective. Some of the must do approaches are so obvious, they should be started today.

Klaus Philipsen, FAIA

SUN article about the reopening of Main Street today.