Spring Creek Flood Field Trip: Stream Discharge & Morphology Analysis

Name Alexi Lindsay Lab Section 16 Spring Creek Field Trip Learning Objectives After completing this lab, you should be able to: 1) Measure stream discharge using the Continuity Equation. 2) Describe the morphology of a stream, including bed material, bank material, channel dimensions, flood plain vegetation, and human alterations. 3) Interpret the characteristics of a stream to determine how a flood would affect the stream. 4) Use an inclinometer to measure the height of an object. Introduction On July 28, 1997 Fort Collins experienced an unusually large urban flood that was centered over the Spring Creek drainage, a tributary of the Cache la Poudre River. Over a 90-minute period on the eve- ning of July 28, up to 5 inches of rain fell within the Spring Creek basin, and a total of 21.3 cm (8.4 inches) of rain was measured in an area centered near Drake Road and Overland Trail, west of the CSU campus near Hughes Stadium. 1 Maximum instantaneous rainfall rates likely exceeded 12.7 – 15.2 cm per hour (5-6 inches per hour) at times. Because of numerous days of rain prior to July 28, infiltration was low, and incredible volumes of water accumulated as runoff, flowing downhill from approximately west to east, initiating the devastating flood in Fort Collins. The flood caused five deaths and millions of dollars of damage, including flooding of Morgan Library and the Lory Student Center, and has become a pivotal event in the development of new floodplain ordinances and flood hazard maps within the City of Fort Collins. Today, you will be visiting the area of Spring Creek at the College Ave. Bridge, just south of Dairy Queen on College Ave. to reconstruct the events of the 1997 Spring Creek Flood and to observe current stream processes. Your task is to: 1) Walk upstream and downstream along Spring Creek and observe elements of the landscape and human development that may have influenced and contributed to the flood hazard, as well as current channel features. 2) Characterize current water flow and channel morphology conditions on Spring Creek. 3) Reconstruct flood conditions, including the maximum flow depth, using photographs of the flood and any current evidence of high water marks. 4) Draw a complete sketch of the area along Spring Creek that depicts the features that contrib- uted to the flood. 5) 5) Hypothesize why the flood was so damaging to this area. 1 Doesken, N.J., and McKee, T.B., 1998, An analysis of rainfall for the July 28, 1997 flood in Ft. Collins, CO, Cli- matology Report 98-1.

GEOL 121: Spring Creek Field Trip Figure 9.1 : Rainfall in Fort Collins from 4:00 p.m. on July 27, 1997 through 11:00 p.m. on July 28, 1997. Source: http:// ccc.atmos.colostate.edu/~odie/rain.html

GEOL 121: Spring Creek Field Trip Assignment Characterize current conditions in Spring Creek 1) (2 pts.) Estimate discharge in m 3 /s (rate of streamflow, measured in water volume per unit of time) by measuring width, depth, and velocity at one location along the stream. Discharge ( Q ) is calculated using the Continuity Equation as follows: Q = w * d * v or Q=vA , where w is average width of flow (m), d is average flow depth (m), and v is average velocity (m/s), and A is channel cross sectional area (m 2 ). Figure 9.2 : Stream discharge is the volume of water moving past a cross section of a river in a given amount of time. Source: USGS: https://water.usgs.gov/edu/streamflow2.html a) Pick a location along the stream for your discharge measurement. Measure the width of the stream at that site using a tape measure. Flow width (m): 3 ½ Flow Width 30.95 seconds 4,397.995 b) Keep your tape measure draped across the stream. Measure the water depth using a meter stick at several points across the stream to get an average depth of the stream at this location. Average flow depth (m): 40.6 Average

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GEOL 121: Spring Creek Field Trip c) Measure the water velocity using some kind of floatable object, Measure the time it takes to travel a certain distance. (Be sure to select a channel reach with some water current.) A channel reach is a section of the creek that you define by its constant channel geometry. Measure the water velocity three times, and take the average. Average flow velocity (m/s): 30.95 seconds d) Calculate the discharge at this location. Discharge (m 3 /s): 0.07259 2) (1 pt.) Discuss two possible sources of error in your discharge estimate. Two possible sources of error in our discharge estimate could be a mistake in the math with our three plug ins of the equation or it could be we missed calculated when we were calculating the water. 3) (1 pt.) If you were to repeat your calculations at a different section of the stream, would you expect the discharge to be different or would it be the same? Why I’d expect the discharge to be relatively the same, maybe a tad bit of change in numbers but nothing drastic as the stream of the water kept pace at all the sites we’ve visited along the creek.

GEOL 121: Spring Creek Field Trip 4) (2 pts.) Test your hypothesis by calculating the discharge at two additional locations along the stream. a) Site 2: Flow width (m): 3.2 Meters Average flow depth (m): 46 cm Average velocity (m/s): 25.5 Discharge (m 3 /s): 0.0586 b) Site 3: Flow width (m): 3 meters Average flow depth (m): 19.5 m Average velocity (m/s): 16.79 Discharge (m 3 /s): 0.03563 5) (1 pt.) Was your hypothesis correct? Why or why not? Our hypothesis was correct as the discharge matched up with our width, depth, and velocity to add up to our discharge.

GEOL 121: Spring Creek Field Trip 6) (4 pts.) The shape, or morphology, of stream channels is influenced by the history of streamflows (climate), sediment supply (climate and geology), the gradient (or slope) of the stream, and, in many cases, human alterations. The gradient measures how steep the stream is, and therefore how much en- ergy it has to transport sediment and erode its banks during floods. Channel gradient is also important during low-flow conditions, and influences the size of the sediment deposited in and along the chan- nel, as well as the types of aquatic organisms that can find habitat in the stream. Gradient has units of meters per meter or feet per mile, and is calculated as rise/run. Gradient can also be visually estimated using qualitative categories (steep, moderate, flat). Select two short reaches of Spring Creek that appear to have different gradients from each other. Draw a plan view of each reach and qualitatively estimate the gradient using one of the categories listed above (steep, moderate, flat). Then describe the morphology of these two reaches, including the characteristics of the 1) bed material (size of sediment, abundance of algae), 2) bank material (natural versus human-placed sediment, size of bank material, vegetation), 3) channel dimensions, 4) flood- plain vegetation, and 5) human alterations. Give quantitative measurements where possible. Clearly label features on the space provided below. Reach 1: Reach 2:

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GEOL 121: Spring Creek Field Trip Reconstruct the Spring Creek flood Figure 9.3: Flooding on Spring Creek near College Ave. Source: CSU Libraries Archive: http://www.colostate.edu/fea- tures/flood97-photos2.aspx Figure 9.4: Flooding on Spring Creek near College Ave. Source: CSU Libraries Archive: http://www.colostate.edu/fea- tures/flood97-photos2.aspx

GEOL 121: Spring Creek Field Trip Figure 9.5: Flooding on Spring Creek near College Ave. Note the high water line indicated by the green arrows. Source: City of Fort Collins Figure 9.6: Flooding on Spring Creek near College Ave. Note the high-water line indicated by the green arrow. Source: City of Fort Collins .

GEOL 121: Spring Creek Field Trip 7) (1 pts.) Look at the pictures on the preceeding pages of Spring Creek during the 1997 flood, and try to match current features that you see with those in the photos. Also note that certain features that are visible in the pictures are no longer present. Select two of the photos and write a short paragraph describing what they show about the Spring Creek flood. The second photo we can see destruction piled up from branches, trash, cars, etc and in the background we can see a recognizable building which in today’s age is Chase bank. It seems as the structure of the building kept it up though I’m not so sure what the entrance of the building was like, most likely flooded with water.The third photo is dairy queen, it seems as the building has always been there just the parking lot is covered in soggy mud spread all around the lot. 8) (2 pts.) Why was the flood so damaging in the area of Spring Creek at College Avenue? Come up with at least three reasons. a. Poor landscaping b. Lack of technology c. Unpreparedness

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GEOL 121: Spring Creek Field Trip 9) (1 pt.) What changes do you see in the area that indicate the City of Fort Collins is trying to remedy flood hazards along Spring Creek? Changes that I saw in the area were higher fractured landscaping placed along the stream of the water followed by a better water flow system starting from the root going west towards horsetooth resovoir. You will now reconstruct flow conditions at this site during the Spring Creek flood. Use the inclinometer on the Brunton compass or the level and tape to help calculate the depth of water in this area. 10) (2 pt.) What was the maximum depth of water in this area, in meters? Include a diagram showing your method of calculating depth of water.

GEOL 121: Spring Creek Field Trip

GEOL 121: Spring Creek Field Trip The estimated discharge ( Q ) at this site during the 1997 flood was approximately 140 m 3 /s (5000 ft 3/ s), or about twice as large as the 500-year flood! Based on the photos of this site, we can infer that flow velocity ( v ) was low here during the flood, because of water backing up behind the College Avenue bridge. 11) (2 pt.) Assuming that flow velocity was approximately 0.5 m/s, use the equation Q=w*d*v to esti- mate the flow width during the flood. This will be a rough estimate, but should give you some idea of how far away from the channel the flood extended (remember that CSU was flooded). Show all your work. Flow width during flood (meters) (or width of ponding at the park): 35 3.43 to pole 1.50 to ground 0.80 cm 0.7 tangent degrees 2.38 4.68 (1 pt.) Discuss two possible sources of error in your width estimate. Two possible sources of error could potentially be our distance from the pole if not another theory of error would be an error of telling the compass.

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