Here we are. . .majoring in minors. . .again.
Watching videos of cars, huge chunks of asphalt, street signs, and all manner of debris cascading down Main Street in Ellicott City, MD. . .six to 8.5 inches of rain fell in just a few hours, and just two years after similar havoc along that very same Main Street. A week or two later, a similar “cell” hit Ivy, VA, just to the west of where I live in Charlottesville. In both cases, lives were lost, property destroyed, infrastructure disassembled, and economies disrupted.
Each of you can tell similar tales or at least knows someone who can.
These types of storms are not the familiar monsters – hurricanes with boys or girls names that announce their arrival days in advance. The ones I am referring to are the nameless spawn. They ride into town on swift steeds, stall out as if targeting a particular neighborhood with malicious intent, unleash their violence, and then depart a few hours later. These monsters are not new; there just seem to be more of them around these days.
A few years ago, Joe Battiata, and I authored a book chapter with the lofty title, Urban Stormwater Management: Evolution of Process and Technology (Hirschman & Battiata, 2016). This chapter may have some value as a sedative, but in it Joe also provides some history of the ever-evolving stormwater/drainage profession (as written by Joe):
The early days of drainage design were largely focused on two systems – the minor system and major system. The minor system, sometimes referred to as the “conveyance system,” consists of curbs, gutters, inlets, pipes, swales, channels, and appurtenant facilities, all designed to minimize nuisance, inconvenience, and hazard to persons and property. The major system consists of the drainage system of natural channels, streams, floodplains, and, in some cases, large man-made systems (e.g. culverts) that carry excess flow over and above the hydraulic capacity of the various components of the minor system. (Hirschman & Battiata, 2016, p. 86).
The chapter goes on to explain the engineering field’s preoccupation with the minor system, the failure to recognize “the importance or even existence of the major system (natural stream network),” and the resulting increase in flooding and stream degradation.
I have been in the water resources profession long enough to see the focus evolve from detention ponds to regional basins to water quality basins to our current LID/green infrastructure focus. In fact, one of my first tasks as a county water manager in the early 1990s was to oversee permit-related monitoring for a large regional pond that controlled over 8,500 acres of urbanizing drainage area. That, in fact, may have been one of the last permits ever approved by regulatory agencies to impound a stream (and a perfectly good one at that) for the purposes of stormwater management. The regional basin approach got shut down due to impacts to aquatic resources, and certainly for good reason. However, along the way, the intent to control stormwater with regional solutions (or even regional thinking) may have also been a casualty. TMDLs certainly take a regional, watershed-based approach, but most have a narrow focus on one or several “pollutants of concern,” and not necessarily the system as a whole.
The continued evolution to LID and green stormwater infrastructure (GSI) has been a major shift from water quality treatment to a more holistic strategy focused on hydrologic impacts. Based on the research, the affect has been positive in terms of runoff volumes, peaks, lag times, and pollutant reductions.
At the same time, we must also note that most definitions of LID or GSI use the terms “decentralized” and “small-scale.” Indeed, that is part of the core philosophy – to capture the runoff close to its source and replicate the hydrologic conditions that may have preceded land development activities. Functionally, that means that drainage areas to LID/GSI practices tend to be small, usually on the order of an acre or two. In other words, these practices function as more advanced components of the minor system, with ambitions to influence the major system in positive ways, if we can just get enough of them in the ground.
With this summer’s monster storms, that is the question – can these distributed practices have a positive impact on not just the “everyday” storms of about one inch of rainfall, but also the big dudes?
Michael Dietz and Chet Arnold tackle this topic in a forum paper entitled, Can Green Infrastructure Provide Both Water Quality and Flood Reduction Benefits? (Dietz and Arnold, 2018). These Connecticut-based land use/stormwater linkage luminaries take a clear-eyed look at the maybe yes, maybe no answer to that question, using several case studies and modelling studies to weigh and sort the evidence.
One thing that caught my attention in the article was reference to a technique for designing temporary flood storage outside of the footprint of the actual stormwater practice, as being currently envisioned in the UK: The approach, termed designing for exceedance, uses green spaces, such as parks, to temporarily store runoff from infrequent events. . .(Dietz and Arnold, 2018, p. 02518001-3).
When I lived in Blacksburg, VA, there was a neighborhood park that did something like that, through the simple construct of a slightly undersized road culvert at the low end of the park. I believe this park was circa 1970s or 80s, so not a product of the GSI wave, but a Town Engineer looking for a simple solution to downstream stormwater issues.
I can only imagine these days the response from the local neighborhood association or PTO to a plan to intentionally flood a park during large storms (social media images of kids clinging to swing sets as the water rises). That said, it is both an old and new idea that warrants further consideration, and will happen either with or without the intention part (see photo below).
Parks Director, B.D., points to the high water mark on play equipment as a result of a recent flood. This is not exactly “designing for exceedance,” but being in a floodplain, the exceedances are inevitable. Can using open space for this use become more deliberate as part of land use and stormwater planning? Certainly, there are costs to clean up flood messes in these spaces, but these are likely much less than having those messes distributed across the broader community and its infrastructure.
Dietz and Arnold are land-use guys who explore the link between land use and stormwater. One thing we have to acknowledge about dealing with the major system is that it is not easy. It is not a turnable knobs type of thing, such as adjusting the depth and composition of bioretention soil media, the underdrain configuration, or how pre-treatment is performed. The major system demands integration with land use planning, with all its unruly mess of human process and political and economic power structures. This may be one of the main reasons that we have majored in minors for all of these years, from the detention ponds of yore to today’s LID/GSI.
I must say that with this summer’s monster storms, and climatic trends pointing to more of these to come, our profession may not be able to afford this luxury or majoring in minors any longer.
We are not going back to the days of massive regional detention ponds, so the solutions will extend to the broader definition of Green Infrastructure (e.g., greenways, river valley parks, reforested areas) linked with technology (e.g., adaptive controls to route flood flows to designated open space storage areas), creative planning and land use retrofitting (move the automobile infrastructure above or below ground), advanced floodplain management (extending the floodplain concept upstream to where there are infrastructure capacity issues), and a renewed commitment to majoring in MAJORS.
NOTE: Chesapeake Bay watershed/stormwater adherents may know that Main Street in Ellicott City is current home of the Chesapeake Stormwater Network as well as former address for the Center for Watershed Protection, which has since moved to higher ground. CSN colleagues indicate that repairs are moving along quickly, and they should be back on their office soon.
References
Dietz, M.E. and Arnold, C.L. (2018). “Can Green Infrastructure Provide Both Water Quality and Flood Reduction Benefits?” Journal of Sustainable Water in the Built Environment (ASCE), 4(2): 02518001-1 — 02518001-5.
Hirschman, D. and Battiata, J. (2016). “Urban Stormwater Management: Evolution of Process and Technology” in Sustainable Water Management in Urban Environments, T. Younous, T.E. Parece (eds.), Hdb Env Chem 47, Springer International Publishing Switzerland, pgs. 83-120.