Sunday, September 9, 2018

What Ellicott City choices teach about adaptation, resilience and values

Ellicott City is everywhere

Ellicott City floods and the response to them, the land planning, adaptation, stormwater management, the emergency response, how to deal with historic preservation and the various types of extreme weather, are all illustrative for any town near water located in a climate zone like ours. That is why the University of Maryland at Baltimore County devoted an entire afternoon seminar to the town under the topic "Meteorology, Hydrology, Emergency Response, and Future Directions" and why the Howard County Council faces difficult decisions.
Buildings on the death list (5 Year Plan presentation to HoCo Council Sept 4, 2018
The academic side, the human side and the failure to be prepared

The academics showed that Ellicott City with its dreadful history of dozens of devastating floods (1868 14 houses were washed away and about 40 people killed) is not a unique case of either bad luck or bad planning. Geography and environmental systems professor Jeffrey Halverston, PhD of UMBC, an expert of severe weather dissected the storms of 2016 and 2018 which devastated the historic mill town for its natural, anthroprogenic and meteorological components.

He and his colleagues have bad news:  Showing national and state maps of Maryland, the experts noted that extreme rainfall and flooding events are on the rise, not only in one unlucky town but especially in the northeast  where some see a 51% increase of extreme precipitation. Halverston illustrated a more moderate upward trend with measurements of flood gages in the Dead Run in Baltimore County.

Rising annual flood peaks of Dead Run tributaries (Prof. Helverston, UMBC)
A look at a Maryland map for this year seems to bear this out. Hadn't Frederick, MD taken extensive flood management measures over the last 30 years, it would have been devastated on may 15 this year, just two weeks ahead of its brethren on the Patapsco and Tiber. Just last week extreme precipitation killed two people in Harford County. Dr Halverston spoke about the increase of tropospheric water vapor, dynamic uplifts, stalled fronts and moisture regenerating echo training. He pointed out that atmospheric responses to small changes are non linear and stayed away from linking his findings directly to global warming.

He as well as his academic colleagues didn't want to be "political" and refrained from any comments about what County Executive Kittleson recently presented in a open air press conference as a 5 year plan to address flash flooding in Ellicott City. The plan and two associated bills are now under consideration by the Howard County Council and the public. (A public hearing will take place on Sept. 17, at 6pm). The procession of academic scientific presentations at UMBC came to an end when Howard County's Director of Emergency Management, Ryan Miller, took the podium and showed storm video footage over the sound of an endless string of 911 calls, evidently in an attempt to add the human dimension.

An unintended effect of his presentation, however, was the demonstration how little emergency management had applied lessons from the 2016 flood in leading up to the second 1000 year rain event and immediately thereafter. How else was it possible that a wedding party with dozens of people could take place in the lower level of La Palapa, one of the structures spanning the Hudson channel at a one of the areas clearly identified as a pinch-point in the 2016 flood,even though a flash flood warning had been issued? (Parts of LaPalapa are proposed to be removed as part of Hudson Bend improvements proposed in the new plan). How else was it possible that the 911 personnel was initially entirely clueless about what was truly going on along Main Street and kept haranguing desperate callers for a precise address when they named a business as their location? How else was it possible that shopkeepers could be trapped on a first floor store without any access to the upper levels of the building they were in? How else was it possible that Main Street hadn't been blocked off for vehicles even after the flooding had already begun once again sweeping cars down Main Street, off parking lots and into the already constricted stream channels? (Over 160 wrecks had to thus be retrieved after the 2018 flood).
Hard to model: Vehicles and debris clogging already restricted channels
The Kittleman/Weinstein 
5 year plan

In the same week as UMBC had their academic extreme weather seminar, Executive Kittleman and Councilman Weinstein  presented their proposal to demolish ten buildings at the foot of Ellicott City's historic Main Street to the County Council. They, too enlisted science (James Lee from the National Weather Service) and engineering (Chris Brooks, Director of Water Resources at McCormick Taylor engineering) and dramatic videos and testimonials.  In the September 4  session they posited stark alternatives: "saving lives or saving buildings" they asked the four council members sitting on the podium. Weinstein's chair was empty since he had taken a seat next to Kittleman in the "witness stand".  The two proffered their 5 year plan as the solution which will allow the town to not only survive its 250 anniversary coming up in four years but also celebrate its 500 birthday in the words of the Executive. Talk about a long range perspective! The 5 year plan is a revised version of the priority list that had been developed in response to the 2016 storm and remains embedded in an overall watershed masterplan which had been scheduled to be complete by now and which will be reopened in light of the second flood.
Hudson Bend improvements include changes to Ellicott Brewing Company and
Las Palapas (Source: 2018 watershed masterplan)

To Kittleman's credit, running for another term as County Executive didn't lead him to punt on the future of the town until after the election, but to demand the kind of urgency which seemed to be somewhat lacking after the first devastating flood of 2016 even though progress was certainly made.  Now he and Weinstein talk a lot about "mother nature" and how in the past the town forced the river to adjust and how the town now needs to adjust to the river.

The plan, as proposed, doesn't really adjust the town to the river, but it sacrifices a good historic chunk which after the 2016 flood was hastily rebuilt. No plan could truly do the tributaries justice, for that Ellicott City is too man-made, the setting along the banks of three steep and narrow streams converging right in its downtown too precarious. In the two recent storms each stream was transporting more water than would fit into the roughly 10' x 20' boxes that form the stream channel underneath buildings at lower Main Street where all three streams are combined, especially when those "underpasses" get clogged with debris, trees and floating cars.  How torrential rain swells the streams and rapidly washes over top their banks is well documented for the flood of May 27 this year, thanks to cameras installed by local citizen Ron Peters who had begun operating the camera network just weeks before the flood event. (Peters is a member of the flood working group).
Dramatic peak flow calculation for the tributaries (UMBC seminar)

Everyone who has studied flooding in Ellicott City knows about the former Caplan's Department store building of 1924. In the floods pushing up from a swelling Patapsco after hurrican Agnes it had been the high watermark. In the flood of 2016 it's first floor was completely devastated. It was then reconstructed with reportedly more than $1 million dollars, including steel beams, concrete floors and steel reinforced walls, indestructible as the owner is apparently claimed and used by Miss Fit as a women's fitness studio. In this year's flood the building was even more destroyed than in the one before. Looking from Main Street one would attribute the damage to its delicate storefront and the fact that it sits in the curve where water rushing down Main Street would shoot cars and flotsam like projectiles into the building. But unbeknownst to tourists walking along the front,  the true threat to Caplan's comes from behind where the New Cut tributary comes down a steep hill being forced to do a 90 degree right turn by the back wall of Caplan's or, in normal conditions by the streamwall on top of which the building sits. When the New Cut was carrying anywhere from 3300 to 6100 cubic feet of water per second in those two recent floods, it pounded on the back of the old department store until the wall gave in, reinforced or not, allowing the torrent to flow through the building, trees and all, releasing a masses of water into Main Street and crushing two floors of the building, leaving only a shell standing.
The elements of the 5 year plan (From presentation to the County Council)

Is this a serious plan?

It takes a lot of studying and investigation to understand what happened in the two recent floods which arose from almost identical meteorological conditions and created very comparable damage in the town. Only at one pinch point there was a striking difference: Where Ellicott Mills Drive meets the center section of Main Street a puny metal pipe culvert was way too small for what came down the Hudson and quickly jumped the stream bed. But in 2016 the water, possibly redirected by the flow coming down on top of Ellicott Mills Drive, aimed for the Methodist AME church, washing away the embankment until the corner of the church hung in the air. In 2018 the Hudson simply took Ellicott Mills Drive out over a stretch of 40' or so, allowing the water to follow gravity, washing the historic court house away in the process then coming to a halt at the 90 degree turn needed to pass under Main Street ("The Hudson Bend").
Sources for the $16.76 million needed

It also takes a lot of studying to review the analysis and models that the flood working group has studied since 2014. Almost any idea and suggestion anybody ever proposed as a solution was investigated by a slew of experts and stakeholders. Still, until the second flash flood hit, the bigger context was a watershed masterplan and a set of flood mitigation concepts developed by the engineering consultant McCormick Taylor which didn't look like true emergency responses with the kind of urgency and radical proposals that the new 5 year plan conveys. This surprised many who expected another round of rebuild when Kittleman presented it on Main Street during a August 23 press conference (see my previous article).

The detailed presentation to the County Council shows that the new plan is not a careless political shot from the hip to demonstrate decisive action but is based on evaluation of alternatives with modeling and calculations performed once again by McCormick Taylor using their two-dimensional hydraulic model based on the 2016 data. The plan combines a variety of upstream measures with various ways to increase downstream conveyance. While this plan was conceived after the second flood and adds new actions to those previously proposed, it is based on professional analysis. With several property owners and flood working group members supporting it and a full public and council consideration coming up, it doesn't appear to be a heavy handed top-down plan. Kittleson indicated that he is not thinking of using eminent domain. The following is an attempt of assessing the strengths and weaknesses of the plan now before the council in the same manner as a councilperson would weigh the pros and cons.
Testimonials from the presentation to the Council

Here a few major take-aways regarding the 5-year plan:
  1. While it is theoretically wiser to address flooding issues with upstream solutions and foolish to attempt "end of pipe solutions" at the bottom of a watershed, Ellicott City is special in that the tributaries converge very far downstream, creating by far the biggest devastation in the last few hundred feet of the watershed where all the assets are. 
  2. While managing stormwater at the source and avoiding run-off is a prudent practice, no current stormwater management regulation or practice can manage precipitations in the range of  3" per half hour or 6" in two hours. Storms of those intensity require a combination of large scale stream retention and increased conveyance.
  3. The 5 year plan presentation included several upstream retention facilities at the Hudson ("Hudson 7"), Quaker Mill retention at Rogers Avenue and potentially also at the Tiber (T1) and the New Cut (NC 3) with water retention capacities of around a half million cubic feet of water each (10-13 acre foot, i.e. 10-13 acres of one foot of water storage). Not all seemed to be included in the funding plan, though.
  4. The plan's demolition of a good number of structures  correctly aims to reduce water depth and velocity outside the safe channels to manageable levels. The focus of attention is on 10 buildings forming the south side of lower Main Street from Caplan's all the way to the train station. The alternatives analysis claims that leaving any parts of the structures which are proposed for demo standing (as Preservation Maryland proposes) would result in less water expansion opportunity due to clogging from debris. 
  5. The demolition plan on lower Main Street also prevents those structures from being damaged by "reverse" floods rising from the Patapsco up. 
  6. The total cost of the 5 year plan is given with $16.76 million not including retention facilities T1 and NC3. 
  7. In the presentation the council was told that work would be phased to begin from the bottom of the river going up.
Precedent: Hebden Bridge, England 2015 flood
The proposed "all of the above" strategy which includes stormwater reduction (development moratorium), upstream water retention, mid and downstream increase of conveyance capacity and floodproofing of structures makes sense. It also makes sense not to open up mid-stream pinch-points without solving downstream conveyance. It probably makes less sense to not fund any of the upstream retention basins, even if such a basin could only hold the extreme flow of the New Cut tributary for less than two minutes (assuming the 2018 reported flow rate of 5,000-6,000 cubic feet per second).

Before deciding on the plan

A full evaluation of the plan is difficult without additional data and clarifications which the Council . will presumably obtain for their upcoming work session. For example, no actual numbers are provided for the current conveyance of the channel where all streams are combined. Nor is there a number given for the maximal capacity which could be reached by lowering the channel or increasing the freeboard by elevating or removing low structures crossing the stream. Nor is any quantitative information given to what extent clogging and debris reduced the theoretical conveyance capacity.

The only gateway to the Patapsco, plus 2 new underground
culverts (Photo: Philipsen)
Most problematic are two questions:

  1. How would a removed Caplan building prevent the New Cut from shooting right into Main Street any more than the Caplan building itself was able to do? 
  2. Perhaps even more troubling is that the proposed building demolition or removal does not truly widen and open the combined stream at its mouth right at the Patapsco. Instead the flow remains impeded by the historic train station and the railroad dam which both present a remaining last pinch-point preventing the water from flowing out. 
The demolition or relocation of the 10 buildings allows water to expand into a kind of small lake behind a dam with limited outflow. This only provides relief if the suggested new double culvert shortcut to the river together with the existing stream channel under the railroad tracks really convey all of the inflow.  This is quite hypothetical and has not yet been demonstrated. Clearly those suggested culvert inlets could clog very quickly. If the combined inflow does not equal the outflow the water would once again use Main Street as its bed trying to reach the Patapsco. If inflow and outflow were, indeed in balance, it wouldn't be necessary to have this water expansion area created through the building removal in the first place. In the presentation the small town of Hebden Bridge in England was shown as a precedent for such a water expansion area. The town looks, indeed, quite similar to Ellicott City and was ravaged by a flood in 2015. Their mitigation plan does not list demolition of historic buildings, though.
184 years in this place: "Tea on the Tiber" building: Proposed for relocation
This building doesn't span the river and sustained no structural damage. What
advantage would its removal bring?

Lastly, given the dramatic eyewitness and victim accounts in the Council presentation, the plan includes no details about building and town evacuation plans, quick response in the case of an impending flash flood, and the avoidance of the massive amounts of debris clogging the already constricted stream channels (Likely all the cars in the channels obstructed the water more than any buildings). Before clobbering preservationists with the false alternative of "lives or buildings", emergency management, emergency communication and code requirements for buildings in the flood zone would have to be effectively addressed. Codes must require safe exits to upper levels of each building and safe routes to higher ground from potentially flooded public areas. It seems to this observer that proof that the removal of 10 buildings is the decisive factor in saving lives through lower flood water levels and reduced flood water velocity in flooding outside the channels, is not fully evident, in spite of the model results that have been provided. 

So far, around the country cities and towns have maybe heightened the defenses, but have generally rebuilt from the New York World Trade Center to Houston and New Orleans. If the HoCo Council will decide for demolishing a part of the town to save it, it will reverberate around the country as a different path towards adaptation, preservation, resilience and lives.

Klaus Philipsen, FAIA

Residents' Letter to the Baltimore SUN in favor of the plan
HoCo flood webpage

No comments:

Post a Comment