City Creek Nature Notes – Salt Lake City

March 19, 2017

March 19th

Filed under: Chuckar, Flood retention pond, Geology, Kingfisher, People, Sounds, Stream — canopus56 @ 7:58 pm

Erosion across Geologic Time

5:00 p.m. Kingfisher! Above Guardhouse Gate, a Belted kingfisher has made its annual migratory appearance. The bird is agitated. As it flies in a circular path a hundred yards in diameter, it makes two-second rapid-fire calls. Usually, the kingfisher is seen at the flood retention pond at Bonneville Drive and Canyon Road. There it perches on a tree next to the upper pond and peers down into the waters looking for its next meal of Brown trout. But the pond was been cleared out by the City that fears an earlier spring flood (March 5th and 16), and for the last week about twenty anglers have been cleaned out both the upper and lower ponds of fish. There is nothing left for the kingfisher to eat. On the drive back home, another early bird sign of spring appears. Three chukars scurry across the road. It is the last day of winter, and the canyon is again busy with an overflowing parking lot. There are about eighty strollers, couples with substitute child-dogs, and bicyclists. Two Rock squirrels scamper across the road. At the pond at picnic site 5, someone has partially pulled out the tree branch that grows horizontally across and below the surface of the pond. The limb has been growing there for about ten years, judging from its size. Fall, trout used this branch as a hiding place. They feed on the water skaters along the outside edge of the pool, but when disturbed by people, the trout bolted underneath the branch (October 21st). Now their hiding place is gone. I am looking forward to the next cycle of annual life and to watching the canyon come fully alive.

The milky high-runoff stream continues its loud roar.

In Thoreau’s “Journal” on March 19th, 1842, he records a strong west wind that generates haze. On March 19th, 1856, he records a 16 inch deep snow. On March 19th, 1858, he sees numerous gnats. He sees redwings. On March 19th, 1859, he notes a strong wind and notes how wind reflects off of blowing trees. On March 19th, 1860, he admires pitch pine trees in the spring light.

The milkiness of the stream reveals that it contains sediments, but is this small stream enough to have carved out the gorge of lower City Creek Canyon below Bonneville Drive over the last 11,000 years? Crudely abstracted, the lower gorge is 2 miles long by 0.1 miles wide and by 200 feet deep, or about 0.008 cubic miles, and it formerly contained about 1.2 billion cubic feet of earth. A rough estimate of sediment transport from City water quality data suggests that the stream could have made the lower gorge over the last 11,000 years.

Most data about water quality in City Creek Canyon is from measurements by the Salt Lake City Department of Public Utilities, but it is easily obtained. The U.S. Geological Survey maintains an archive of water quality and volume measurements of City Creek, including the City’s data, as part of its National Water Information System (U.S.G.S. 2017c), and a set of water quality measurements from 1964 to 1966 includes the dry weight of dissolved solids in City Creek stream water. The stream transports a surprisingly wide range of daily weight of solids down the canyon, but in terms of unitized acre-feet of stream flow, the stream transports a steady proportion of about 0.4 tonnes of dry solids in each acre-foot of water. City Creek stream flow data from the National Resources Conservation Service gives a mean annual flow for the stream of about 11,700 acre-feet per year (NRCS 2017), soils in Utah typically contain about 35 percent water, and a cubic foot of soil weights about 100 pounds. Putting all of this together gives a rough first-order estimate that little City Creek stream has transported about 1.5 billion tonnes of sediment to the delta over the last 11,000 years*. Over geologic time, City Creek’s little stream could have carved out the lower canyon gorge, and this estimate excludes extreme flooding events, like the flood of 1983, where the canyon’s flood waters run as a thick, dark red mass of mud, silt, and boulders.

* – 11,700 acre-feet per year x 0.4 tonnes dry weight per acre-foot divided by 0.65 percent dry weight x 11,000 years x 2,000 pounds per ton divided by 100 pounds per cubic foot of soil = 1.489 billion cubic feet.

On March 19th, 1892, Mayor Baskin and the City Council met at the old Silk Mill to decide if it should be torn down (Deseret Weekly).

Advertisements

Leave a Comment »

No comments yet.

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Blog at WordPress.com.