Monday, September 23, 2019

Painting River Depth Markers

The Assabet River, as it flows through Maynard, has an average volume of 200 cubic feet per second (cfs). Month-by-month, March and April average 400 cfs, while July, August and September average under 100 cfs. Drought can drop flow to 20 cfs. There is an internet-accessible gauge of river volume and depth, found by searching on USGS Assabet. The default is showing the last seven days of data, but a larger number of days can be selected.

At 100 cfs, depth is 2.0 feet, 200 cfs = 2.5 feet, 300 cfs = 3.0 feet, 400 cfs = 3.5 feet,
1,000 cfs = 5.0 feet, 1,700 cfs = 6.0 feet, and 2,400 cfs = 7.0 feet. The last significant flood was spring 2010, 2,500 cfs = 7.1 feet.
Wall under John's Cleaners, bordering the Assabet River in Maynard, MA, as
seen from the middle of the Main Street bridge. Click on photos to enlarge
While checking USGS Assabet is rewarding to data advocates, the idea of providing a publicly seen measure of water depth was a challenge. One location seemed ideal - the wall under John's Cleaners, bordering the Assabet River, next to the Main Street bridge.
Walking in the Assabet River from Tobin Park (north of the Rail Trail bridge)
 to the Main Street site, where a ladder had been lowered by rope.
As this was to be a very public project, seeking permissions seemed like a good idea. Queries to Town of Maynard management, including Department of Public Works and Conservation Commission, resulted in conditional approval. Facts learned in the process were that the Commonwealth of Massachusetts 'owns' the water in the river, the Town owns the land under the river, and private property owners own land down to mean high water. What this meant was that John's Cleaners owns the wall, so permission was sought there, also. Finally, the project was proposed to the Board of Selectmen - and approved. A waiver was signed to absolve the Town of any liability in case of injury.
Using duct tape to attach a stencil to the wall. Two stencils were created, each five feet long
one taped above the other. The material was FedEx boxes. Making the stencils took four hours.
Stencils were created from FedEx corrugated boxes, incorporating five inch tall number stencils. Creating the stencils took about four hours. The duct tape and stencils were lowered by rope from the bridge. Discarded after the one-time use.
The paint use was Benjamin Marine D.M.T. Acrylic "Safety White,"
suitable for use in places that will be wet or under water.
From arriving at the site to completion of the painting took about one hour, including the walk in from and out to Tobin Park, which was over water-plant slicked rocks under one to two feet of water. The ladder was needed to tape and then paint the top of the upper stencil.
About to paint the top markers and numbers. Nine feet was chosen because since record
keeping began in 1942, no flood has exceeded nine feet, and only five have exceeded seven feet. 
Water depth records collected by the U.S. Geological Survey (USGS Assabet) are for the gauge near the 7-11 store, and thus water depth at the bridge is not an exact match. The USGS defines the Assabet River as being in flood stage when depth exceed five feet. This happens at least once almost every year.
Wall painted, stencils removed. Except in time of extreme drought
the water is never low enough to paint a marker for one foot.
Historically, for floods for which water depth was measured, Hurricane Diane raised the river to 8.94 feet (at the gauge) in 1955. Floods in 1968 and 1979 reached 8.1 feet. Floods in 1987 and 2010 reached 7.1 feet. Volume at that 2010 flood was recorded as 2,500 cubic feet per second.
The wall, with water depth markers.
River depth is of interest to kayakers. Currently the river between the Ben Smith Dam and the east side of Maynard is blocked by many fallen trees, but if ever cleared (by Town of Maynard, or a significant flood), it is possible to kayak through town - under the bridges - when water depth is more than 2.5 feet and less than 4.0 feet. Too low, get stuck on bottom. Too high, get stuck under bridges.

1 comment:

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