Physical Characteristics of the Emigration Creek Ecosystem

( Nathan Owens)

Index:

Location Surroundings Stream Substrate
Stream Flow, Width, Depth, and Discharge Water Temperature Physical Features
  References  

Location:

        The section of Emigration Creek that we are studying runs across 1300 East and about 1800 South. The creek runs alongside the southern edge of the Westminster College campus for approximately 1/8 of a mile. The stream is fed by the Emigration watershed of the Wasatch Mountains, east of Salt Lake City. In addition to watershed runoffs, the stream also collects water from urban stormdrains in eastern Salt Lake City.

 

 

 

Surroundings:

 

            The creek is located between the Giovale Library and the new residence halls on the south side of campus. The residence halls and other buildings have  been built near the creek.  There have been large cement blocks left behind in the creek bed and on the banks of the creek by the crews working on various construction projects in the past. In addition, two building drains and two parking lot storm drains enter the creek at four different points ( see map ).

            The banks of the creek are relatively steep due to past entrenchment and erosion.  The creek crosses a relatively recent escarpment of the Wasatch Fault just west of 1300 East (Link to URL of Wasatch Fault map) which steepens the gradient for water flow velocity.  Narrow footpaths have been created on both sides of the creek by volunteers to allow access to the streambed at various points.   As a result of the steep embankments, sediment  is eroded from this reach during high spring runoff or flood events.  

            There are many native riparain trees along the creek on both banks. The main species of trees  are the Box Elder , the Fremont Cottonwood , the Peachleaf Willow , and the Lanceleaf Cottonwood (Populus. acuminata ), which is a hybrid between the Fremont Cottonwood and the Narrowleaf Cottonwood .   The dense roots of the cottonwood and willow trees that line the stream banks, often emerge into the creek water.  Often pink in color, these roots play a significant role in capturing and holding stream sediment as well as protecting the streambank from erosion during high flood flows.

 The east reach of the creek bed tends to receive less sunlight compared to the more western reach, due to the dense tree cover.  In addition, the stream is more deeply entrenched and flows more rapidly the further east you go toward 1300 East. The creek tends to meander and flow more slowly toward the west. Consequently, more algae and diatoms are found in the shallow riffles of the western reach since more light reaches the creek bed.

Stream Substrate:

 Most of the substrate of the streambed is somewhat large rocks, with the average diameter being around 7.0 inches.  

Planaria, snails, mayflies, and a variety of other aquatic invertebrates live under these rocks and cobbles. These rocks 

provide protection from both predators and faster moving water, especially during spring runoff events and summer 

storm pulses.   Since  the streambed is armored by larger cobbles and rocks it is not a significant source of sediment.  

Permanent stream profile markers have been established and surveyed by students to document long-term 

entrenchment.  The one-hundred year flood event during 1983-84 created two major gravel alluvium deposits along 

the inner sides of two major meanders (see map).  These flood terraces have since been re-vegetated (see discussion 

below)        

 

Stream Flow, Width, Depth, and Discharge:

            The minimum discharge volume for Emigration Creek was estimated on December 4, 2000 using the following method: The velocity of the stream was determined by timing a floating object between two points one hundred feet apart from one another. I did this three times in a section of the creek that was relatively even ( no bends ) without any riffles or abrupt fluctuations in stream width. I then took the average of these three values, and determined the average velocity of this section of Emigration Creek to be approximately .75 ft/s. There had been nice, sunny weather the previous week, and no storms had occurred. This value, is therefore, a minimum seasonal flow volume. Much of this baseline flow is due to seeps and springs in the canyon watershed.

            The average width of the stream was obtained by measuring the width of the stream in three different places that seemed to represent the overall width of the stream. I then calculated the average of these widths to obtain the average width of the stream. This turned out to be approximately 16 feet. The creek is relatively shallow in most places along this section, with very few areas reaching more than one foot in depth. I measured the average depth of the stream in three different points along the same stretch of the creek that I used to measure the average velocity of the creek. I then took these average depths in these three points and obtained the average of these average depths to obtain the average depth of the creek. I found this to be approximately 6.5 inches.

This indicates that the substrate factor for the creek is .7 , according to the scale:

                                               

Substrate Factor:   ( Dr. Robert Pennak, University of Colorado)

.9 for sandy or muddy bottom
.8 for gravel

 .7 for cobbles ( 1-11 inches )

 .7 for boulders ( greater than 12 inches in diameter )     

 

The discharge of the stream can be calculated from the known values of average width ( W ), average depth ( D ), substrate factor (a ), the length of the area measured ( L ), and the time that it took for the floating object to travel the length of the measured area ( t ). This formula can be written as

                                   

Discharge   W*D*a*L
      T

 

                                                        

 

From this equation, I calculated the discharge of the stream to be about 4.55 cubic feet per second ( ft^3/sec ).

 Temperature of the Creek:

 

         On November 24,2000, I found the temperature of the creek by using a CBL ( computer-based laboratory ) unit to determine the temperature of the creek in three different places. The average water temperature came out to be approximately 8.2 degrees Celsius. The graph below displays the typical temperature of Emigration Creek during the fall ( from Natural World Class at Westminster College, Fall '99 ). The cooler water temperatures during November were due to a series of snowstorms and cool weather during that month. For the chemical characteristics of the creek, see the Chemical Features page.

 

 

For more information regarding average precipitation and temperatures, visit the watershed webpage.

 

Physical Features of Emigration Creek:

 

Reach #6 is probably the most diverse reach of the stream in terms of physical features. It seems that this reach holds much of the debris that floats down from further up the stream. The reach is approximately about 24 meters long.

There are several physical features that make a significant impact in the formation of this reach.  One of the biggest was a fallen tree, which lies from the base of the second flood plain across the creek and lies upon the opposite bank.  The tree is 1.1 meters thick and 17.8 meters long. Most of the debris that is washed downstream tends to collect in the branches of this tree. In effect, the tree serves as a natural dam. Like the other reaches, this reach also has a steep embankment on its southern side.  The creek is undercutting the hillside with the strongest part of the current on that south side. Branches from the fallen Fremont Cottonwood in the streambed were removed in May 2000 by Salt Lake County Flood Control. However, the meter- thick trunk remains on the flood plains of the creek.

There is a deposition bar at the far northwestern side of the creek bed in reach 6. This sand bar was formed as a result of the strong current at the meandering point of the southwestern side.  The southern current carries much of the sediment further down stream.  This causes the sediment carried by the slower north side current to fall and deposit on that northern side, creating a sandy deposit or bar. This deposit was created during the flood flows of 1983-1984 and has since been revegetated by grasses.

There are three flood terraces in Reach 6.  The first is only .10 meters above the standard water level of the creek.  This flood plain runs the entire length of the reach on the northern side.  The second flood plain is 1.1 meters above the standard water level.  This flood plain is used when more than a fair amount of water is added to the current water level during spring snowmelt events. The third flood plain was the 100-year flood plain.  It formed the sides of the reach and is 12.2 meters high at the deepest point. ( Sloan, Terry: Class Report from The Natural World (Biol 102)Fall 2000)

References

Terry Sloan, Natural World Class Report, Biology Dept. at Westminster College, Fall 1999

Dr. Robert Pennak, University of Colorado

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