JFS Engineering
Land Development and Water Resources Engineering
Flaky Logic: Snow Storage
Categories: Design Vignettes
Snow Storage: It's a thorny issue (photo courtesy of Robert Schilare Photography)

Snow Storage: It’s a thorny issue (photo courtesy of Robert Schilare Photography)

Snow, snow storage, ice, and frost are things that we rarely discuss in engineering circles. You will see these words in an Earthwork specification: “Do not work frozen material, snow, or ice.” Frozen material is ever shifting and dynamic. Our photo for this month shows what happened to snow after some freeze-thaw cycles. Turned into a spongy block of ice, it’s a beautiful example of how snow melts, refreezes, and transforms like a living creature.

There are some examples of ice being used for roads and buildings. During the Revolutionary War, Henry Knox spent a few bitter cold evenings out on the Hudson drilling the thin ice; the water bubbled through and re-froze to create a sheet thick enough to support cannons. In Canada and Russia, ice roads are used frequently as impromptu truck routes. Igloos are an indigenous structure made from ice and snow.

Conversely, we can avoid ice and frost with good site design. Storm sewers tend to not choke with ice during the winter because the Earth’s heat keeps runoff liquid, if not warm. Providing good pitch to paved surfaces can minimize ice formation, and using a pervious pavement can eliminate the need for salt and sand. Need to look for sanitary connections to storm sewers? Just ride around on a winter morning and look for a steaming catch basin.

We can design around snow storage. Some Canadian provinces have codified their snow storage design parameters (NRCS has guidance as well). Typically they use an equivalent depth ratio, 10S:1P, where S is snow and P is precipitation. So if we assume an average of 4 inches precipitation per month, then we can design around 40 inches of snow. They also specify a compaction ratio, 5N:1C, where N is new snow depth and C is compacted snow depth. Add in a 1H:1V angle of repose, assume accumulation from November to April, and we can engineer snow storage for a parking lot.

It is common for small businesses in a Central Business District to get a ticket for not clearing snow and ice from the sidewalk. It is here that we run into another tragedy of the commons, what to do with the snow. So in a hypothetical situation, let’s use 10 inches of snowfall with a 20 foot wide sidewalk and a 20 foot wide storefront. That’s 67 cubic feet of snow.

The obvious solution is to mound the snow up in front of the building, leaving a walking path. This is also the worst thing our harried shopkeeper can do. Snowmelt trapped against the building rots out the front sill as ice re-forms on the same sidewalk. Push it all to the curb and giggle as patrons cross a miniature version of the Alps? Funny, but no. Alas, this is actually what happens. For the sake of clearing the sidewalk, we make our coveted parking spaces partially useless and dangerous. Not to mention now that snow on a sidewalk ramp puts it out of ADA compliance.

As we see it, there are three forgotten heroes who can save us from our own folly: Tree pits, Public benches, and temporary banked parking. For a moment, let’s ignore the dubious practice of carting snow away. It’s a cop out, and although it works, more thoughtful design can be applied to find a more elegant solution.

Let’s take the standard tree pit at 3 feet wide with a 6 inch deep depression. The pit can store 3.75 cubic feet per linear foot, so it would need to be 18 feet long to store all the snow. For smaller storms the standard tree pit may work, but it’s not a scalable solution.

Storing snow on a public bench? Sounds like an idea only an engineer could love, but hear me out. The bench is generally unused or unusable when there is snow, and the seat doubles as a shelf. Assuming we pack the bottom solid and can use the seat back for support, we can squirrel away a full 27 cubic feet of snow on an 8 foot bench.

Using a banked parking space, we can develop a mound of snow about 8 feet wide by 20 feet long at the base. In that 265 cubic feet of storage we find solace for 4 shopkeepers. If we locate the banked space (or spaces) at a catch basin, icing is minimized. Designate a banked space with a temporary barrier before the snow falls and shovel all the sidewalk snow into a heap right there. Considering the alternatives, the loss of one space here is to gain full access to the sidewalks everywhere else is a small price to pay. Things become less elegant when we think about snow storage from a zoning perspective.

What we find fascinating is that in the agony over parking lot design and permitting, it’s only rarely that the issue of snow storage comes up here in New Jersey. If we consider parking requirements as a static situation, then the assumption is that when a use is in operation that the lot will be full. Believe it or not, this is how most zoning ordinances are still written. The times this does hold true tend to be from late October through until late December, the peak holiday shopping season. Come January, we know that most stores will be lightly attended, but the end-of-year snowstorms can just add to holiday frustration.

Now we all know what shopping centers usually do with their snow. It’s pushed into a big mound near the back of the parking lot. These urban glaciers finally thaw out by late Spring. Silence is prohibition in zoning, and based on the way many ordinances are written, outdoor material storage is considered an accessory use. Outdoor storage of material without an approved site plan, now that’s just crazy. Zoning citations over a parking lot glacier is a little silly, and generally unheard of, no matter how much of a parking variance was needed during approvals. Yet, through all of this, it seems as though the stores still manage to stay open and find a way to cope with a sudden loss of parking provided during the busy season. Although snow storage is a seasonal issue, this fact points to the logical fault in “square footage generates parking demand.” Something to ponder the next time you’re out shoveling snow.

 

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