Field Observations and One-Dimensional Flow Modeling of Summit Creek in Mack Park, Smithfield, Utah

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1 Sediment Transport Workshop, Utah State University, 1 August 2017 Field Observations and One-Dimensional Flow Modeling of Summit Creek in Mack Park, Smithfield, Utah I. Goals for learning and discussion: A. Learn to use HEC-RAS, by building a working steady state model B. Learn the relation among model inputs, model-derived outputs, and actual field conditions C. After this session, students will be able to construct a basic HEC model and will be ready to learn how to tackle more complicated modeling scenarios. II. Activity: After eating lunch, we will walk along the channel and identify the locations of channel crosssections and bed material counts. Your observations will be useful when you return to the class room and build the model. Background: Summit Creek is a small tributary of the Bear River that drains part of the Bear River Range. Mack Park is a 13-ac tract that was deeded to Smithfield city in Originally, the area was referred to as the Grove because of the trees, willows, and shrubbery (Smithfield Historical Society, 2001). The map of the park from 1934 depicted a heavily wooded area around the stream. The stream was shown approximately at the same location as it is today. The present landscape of the park was created in the late 1970s following numerous complaints about rowdy parties and misuse. Diseased and dead trees were removed. Unsightly underbrush and willows were cleared away from the creek banks. The city crews graded some of the areas and riprapped the banks of the creek. New trees and grass were planted where needed. The completed project cost about $10,000 (Smithfield Historical Society, 2001). Comparison of the location of today s channel with that of 1934 indicates that some degree of realignment occurred during these construction activities. Stream flow The USGS operated gaging station between 1961 and 1979 approximately 4 mi upstream from the park (Fig. 1) where the drainage basin area is 11.6 mi 2. The mean annual flow for this period was 19.8 ft 3 /s and varied over a three-fold range between 8.1 and 29.1 ft 3 /s (Fig. 2). The largest flood of the gaging period was 302 ft 3 /s and occurred May 23, This flood was approximately 15 times larger than the mean annual flow. The 2-yr recurrence flood is approximately 145 ft 3 /s, which is approximately 7 times larger than the mean annual flow. Flood frequency analysis indicates that the 1.5-yr recurrence flood at the gage is approximately 76 ft 3 /s and that the 2-yr recurrence flood is 149 ft 3 /s (Fig. 3).

2 Stream flow through the park has two origins: natural flood flows generated from the watershed and base flows derived from irrigation return flows from canals. There are three diversions of stream flow between the USGS gage and Mack Park (Photo 1), and most base flows are diverted from the stream. The base flows that you observe are primarily derived from water that is not diverted and flow that enters the stream from the Logan, Hyde Park, and Smithfield Canal originally diverted from the Logan River. In contrast, flood flows are typically derived from the Summit Creek watershed, because they occur at a time when diversions are minimal. There is no regular measurement of stream flow in the park. We have developed a stage-discharge rating relation. Over a stage range of approximately 1.8 ft, discharge varies between approximately 0 and 129 ft 3 /s (Fig. 4). Geomorphology The water surface slope through the park is between and , depending on the stage at which measurements are made (Fig. 5). The reach within 30 m upstream from the lower concrete bridge is the steepest part of the profile. The bed material of the channel is highly variable, because many blocks or rip rap have now fallen into the channel and contribute to hydraulic roughness. Thus, we completed two bed material counts (Fig. 6) that were isolated to specific bars in the park, located in Figure 7. In addition, we completed one surface material count that averaged bed material of the entire channel between cross-sections 8 and 18, one surface material count from Canyon Road to Middle Bridge (Fig.7), one surface material count that averaged the reach between the middle and downstream bridges, and one count that characterized the average bed material size upstream from Canyon Road. We also completed one subsurface bed material count at gravel bar 2 in the park. Since bed material size, bed material organization, bank material, and plan form all contribute to hydraulic roughness, you should observe channel conditions as you walk around. Examine the example cross-sections shown in Figure 8 and note the edges of the active bed, bank material, and the sloping grassy surfaces of the park. You will need to identify the edges of the bank when building your HEC-RAS model and so your field notes will be useful later today. HEC-RAS modeling exercise When you return to the classroom, you are to build a HEC-RAS model of Summit Creek between cross-sections 1 and 18. The cross-section data, including the distance between cross-sections, are included in an Excel file.

3 Summit Creek, Smithfield, Utah Photo 1. Diversion on Summit Creek, about 0.7miles upstream from Mack Park. July 8, 2008 (~ 2.62 ft 3 /s) June 8, 2009 (~ 130 ft 3 /s) August 4, 2009 Photo 2. Stream character upstream from Mack Park

4 Summit Creek, Smithfield, Utah June 8, 2009 (~ 130 ft 3 /s) August 4, 2009 July 8, 2008 (~ 2.62 ft 3 /s) Photo 3. Stream character in Mack Park. July 8, 2008 (~ 2.62 ft 3 /s) August 4, 2009 Photo 4. Change of river bed in Mack Park.

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12 Figure 8 Example cross-sections, Summit Creek at Mack Park 99 Summit Creek XS-1 Elevation, in meters, above an arbitrary datum Distance from left endpoint, in meters, from an arbitrary datum a) 99 Summit Creek XS-2 Elevation, in meters, above an arbitrary datum Distance from left endpoint, in meters, from an arbitrary datum b)

13 100 Summit Creek XS-11 Elevation, in meters, above an arbitrary datum Distance from left endpoint, in meters, from an arbitrary datum c) 100 Summit Creek XS-12 Elevation, in meters, above an arbitrary datum Distance from left endpoint, in meters, from an arbitrary datum d)

14 101 Summit Creek XS-17 Elevation, in meters, above an arbitrary datum Distance from left endpoint, in meters, from an arbitrary datum e) 101 Summit Creek XS-18 Elevation, in meters, above an arbitrary datum Distance from left endpoint, in meters, from an arbitrary datum f)

15 Day 2 RAS Exercise - Summit Creek The goal of this exercise is to construct and calibrate a working RAS model of the Mack Park section of Summit Creek. Then you will use it to estimate water surface elevations for a wide range of discharges. These instructions assume a basic knowledge of HEC- RAS. Step 1 CREATE A NEW PROJECT - Create a new project by clicking <File> <New Project> - Choose an existing folder or create a new one by clicking the <Create Folder> button - Enter a Title and a File Name and hit <OK> The program will create the new project in English units. - Click <options> <unit system> and select SI units for our metric data. Step 2 ENTER AND EDIT GEOMETRIC DATA - Begin entering geometry data by clicking <Edit> <Geometric Data> - Then, in the new window, click <File> <New Geometry Data> - Enter a Title and click <OK> - In the empty geometry data window, click the River Reach tool and draw in a simple channel, ending with a double click: a straight line will do. When you double click, a box will appear. Enter a River name and a Reach name. Choose something creative like Summit Creek for the river name and Mack Park for the reach name, then click OK. - Next, click the Cross Section tool and choose <Options> <Add a new Cross Section> - In the box that appears, enter the river station for the section that will be entered. Remember that HEC requires that the lowest river station number be at the downstream end and that station numbers increase in the upstream direction. The input data for your cross sections are contained in the posted Excel spreadsheet. Data includes; station and elevation points (cross section data from left to right when looking downstream), bank stations (left and right), and downstream reach lengths for the left overbank (LOB), channel, and right overbank (ROB). You will also need to guess at a Manning s n for your channel and overbank areas. You will adjust the n value later in the exercise, when you calibrate the model. Contraction and expansion coefficients can be set to 0.1 and 0.3 respectively. After entering your cross section data, click <apply data>, and the plot of your data will be updated with your changes. When you are satisfied with your cross section, begin entering data for the next section by clicking <options> <Add new Cross Section>, and repeat the procedure outlined above. When all section data has been entered, close the cross section editor. You should see that the sections have been added to the schematic plot of the river. Save the geometry data by clicking <File> <Save Geometry Data> and giving it a name. Close the geometric data window

16 Step 3 ENTER AND EDIT STEADY FLOW DATA - Begin entering steady flow data by clicking <edit> <Steady Flow Data>. - Enter the number of profiles (discharges in cfs) that are to be entered. To begin with, choose 3 profiles. - Enter the 3 calibration discharges of cms ( cfs), cms (38.5 cfs), and cms (2.62 cfs), into the table by the station number. - Enter the profile names by clicking <options> <edit profile names> and entering a descriptive name for each profile, then click OK. - Now click the Reach Boundary Conditions button. We will use a known water surface boundary condition, so click that button and enter the known water surfaces for the downstream section into the box for each of our 3 calibration discharges, and click OK. Click OK to close the boundary condition editor. - Next, we will enter the surveyed water surface elevations from the Excel spreadsheet. While still working in the steady flow data editor, click <Options> <Observed WS>. A new box will open that allows water surface elevations to be entered for each river station. Enter the data into the proper row and click OK. Save the steady flow data by clicking <File> <Save Flow Data>, entering a name for the steady flow data, and clicking OK. Close the steady flow data editor. Your HEC model is now ready to run. Step 4 RUN THE MODEL To run the model, click <Run> <Steady Flow Analysis>. In the steady flow analysis window, make sure the subcritical radio button is selected, and then click the large COMPUTE button. If everything works, you should see a quick-moving blue computation bar and then the program will show you a short message about the model run. Click the Close button. The model run is now complete. You can examine your results in many ways. Begin by clicking on the tool buttons for View cross sections and View profiles. In these windows, click <options> <variables>, and turn on the observed water surface elevations by clicking the appropriate box. Take a look at the long profile and several cross sections and compare your water surface elevations to the surveyed elevations. How well do your computed water surface elevations match the surveys?? Do you need to calibrate? Step 5 CALIBRATE YOUR MODEL For each of the flows of 2.62 ft 3 /s, 38.5 ft 3 /s, and 129 ft 3 /s, compare your predicted water surface slope with the actual water surface measured in the field. To calibrate your model, you can vary n values to obtain better agreement between the computed and the surveyed WSEL. Increasing n values will raise the computed water surface: decreasing n will lower it. Try to adjust the n values to get your modeled values to match the surveys. You can do this one section at a time, using different values for n at each section, or you can use the same value for all sections. We will discuss the relative merits of each method in class. When you are satisfied with your model, make sure your geometry file is saved. You can add additional discharges to the model by adding more profiles to the steady flow editor and specifying a discharge. We will also show you another roughness method. At this point, we will get the group together and discuss your results.

17 HOMEWORK (I) Determine the capacity of the channel before flows inundate areas used by the public. Using the flood frequency plot, determine the frequency of this inundation. (II) With your calibrated RAS model, extract an output table that includes shear stress in the channel (Shear Chan). RAS will report values for each section for each of the three flows. You also have grain size information in Figure 6. The critical Shields Number * c c ( s 1) gd can be used to estimate the onset of sediment motion. If one uses the median size of the gravel portion of the surface grain size for each bar, a reasonable value of critical Shields Number is * c 0.03 You have all the pieces. Estimate the discharge at which sediment begins moving on the two bars. (s = ρ s /ρ = 2.65; ρ = 1,000 kg/m 3, and g = 9.81 m/s 2 ). Make sure you have RAS report shear in N/m 2 ). We will discuss the results in the morning. [Spoiler alert: you are unlikely to find a definitive answer to this problem!]