E X A M P L E 8
Looped Network
Purpo
This example was performed to demonstrate the analysis of a river reach that
contains a loop. The loop is caud by a split in the main channel that forms
two streams which join back together.
广州美甲培训学校The focus of this example is on the development of the looped network and
the balancing of the flows through each branch of the loop. The stream
junctions will be discusd briefly; however, a more detailed discussion of
stream junctions can be found in example 10.
To review the data files for this example, from the main program window免费英语翻译软件
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lect File and then Open Project. Select the project labeled “Looped
Network - Example 8.” This will open the project and activate the following
files:
Plan :“Looped Plan”
排列顺序Geometry :“Looped Geometry”
英语职称考试报名Flow :“10, 50, and 100 year flow events”Geometric Data
The geometric data for this example consists of the river system schematic,
the cross ction data, and the stream junction data. Each of the
czechcomponents are discusd below.
River System Schematic
To view the river system schematic, from the main program window lect
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Edit and then Geometric Data. This will activate the Geometric Data
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Editor and display the river system schematic as shown in Figure 8.1. The
schematic shows the layout of the two rivers. Spruce Creek is broken into
three river reaches: Upper Spruce Creek, Middle Spruce Creek, Lower
Spruce Creek. Bear Run is left as a single river reach. The flow in Upper
Spruce Creek splits at Tusyville to form Bear Run and Middle Spruce
Creek. Bear Run is approximately 1500 feet in length and Middle Spruce
Creek is approximately 1000 feet long. The two streams then join atmillet
Coburn to form Lower Spruce Creek.
Figure 8.1 River System Schematic for Spruce Creek and Bear Run Cross Section Data
After the river reaches were sketched to form the river system schematic, the cross ction data were entered. The data were entered by lecting the Cross Section icon from the Geometric Data Editor. For each cross ction, the geometric data consisted of the : X-Y coordinates, downstream reach lengths, Manning’s n values, main channel bank stations, the contraction and expansion coefficients, and, if applicable, left or right levees.
After all of the geometric data were entered, File and then Save Geometry Data As were lected from the Geometric Data Editor. The title “Looped Geometry” was entered and the OK button lected. This was the only
geometry file for this example.
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Figure 8.2 Junction Data Editor for Tusyville Junction
Stream Junction Data
The final geometric component was the data for the stream junction. The data were entered by lecting the Junction icon on the Geometric Data Editor . This caud the Junction Data Editor to appear as shown in Figure
8.2. First, the data for the junction at Tusyville was entered by lecting the appropriate Junction Name at the top of the editor. Then a Description was entered as “Spruce Creek Split.”
The next piece of information required was the Length Across Junction . The are the distances from the downstream river station of Upper Spruce to the upstream river stations of Middle Spruce and Bear Run. In general, the cross ctions that bound a junction should be placed as clo to the junction as possible. This will allow for a more accurate calculation of the energy loss across the junction. The values were entered as 80 and 70 feet, for the distances to Middle Spruce and Bear Run, respectively.
The last item in the junction editor is the computation mode. Either the Energy or the Momentum m
ethod must be lected. The energy method (the default method) us a standard step procedure to determine the water surface across the junction. The momentum method takes into account the angle of the tributaries to evaluate the forces associated with the tributary flows. For this example, the flow velocities were low and the influence of the tributary angle was considered insignificant. Therefore, the energy method was lected for the analysis. For a further discussion on stream junctions, the ur is referred to example 10 and to chapter 4 of the Hydraulic Reference Manual .
After the data were entered for the Tusyville Junction, the Apply Data button was lected. The down arrow adjacent to the Junction Name was depresd to activate the cond junction at Coburn. At this junction, the
Figure 8.3 Steady Flow Data Editor - Looped Plan - 1st Flow
Distribution
description “Confluence of Bear Run and Middle Spruce” was entered. Next,a length of 70 feet was entered from Bear Run to Lower Spruce and 85 feet for the distance from Middle Spruce to Lower Spruce. Again, the energy method was lected and the Apply Data button was chon before closing the junction editor.
Steady Flow Data
The steady flow data were entered next. The data consisted of the profile data and the boundary conditions. Each of the items is discusd as follows.
Profile Data
To enter the steady flow data, the Steady Flow Data Editor was activated from the main program window by lecting Edit and then Steady Flow Data . This opened the editor as shown in Figure 8.3. On the first line of the editor, the number of profiles was chon to be 3. The profiles will reprent the 10, 50, and 100 - year flow events. When the number of profiles is entered, the table e
xpands to provide a column for each profile.
To enter the flow data, a flow value must be entered at the upstream end of each reach. The program will consider the flow rate to be constant throughout the reach unless a change in flow location is entered. For this example, the flow will be constant throughout each reach. The three profiles will be for flow values of 300, 800, and 1000 cfs. The values were entered as the flow rates for Upper Spruce and Lower Spruce.
For the flow rates through Middle Spruce and Bear Run, the ur must estimate the amount of flow for each reach. Then, after the analysis, the ur must compare the energy values at the upstream ends of Middle Spruce and Bear Run. If the energy values differ by a significant amount, then the flow rates through the two reaches must be redistributed and a cond analysis performed. This process will continue until the upstream energies are within a reasonable tolerance. This procedure implies that the upstream cross ctions of Middle Spruce and Bear Run are located clo to the junction. Therefore, the energy value at the two locations should be approximately equal.
For this first attempt at a flow distribution, the values of 170 and 130 cfs were entered for the first profile for Middle Spruce and Bear Run, respectively. Similarly, flow values of 450 and 350 were ente
red for the cond profile and 560 and 440 for the third profile. After the analysis, the upstream energies for each profile were compared to determine if the flow distribution was appropriate. This will be discusd in a subquent ction.
Boundary Conditions
After the flow data were entered, the boundary conditions were established. This was performed by lecting the Boundary Conditions icon from the top of the Steady Flow Data Editor. This resulted in the display as shown in Figure 8.4. As shown in Figure 8.4, the boundary conditions table will automatically contain any internal boundary conditions such as stream junctions. The ur is required to enter the external boundary conditions. For this example, a subcritical flow analysis was performed; therefore, the external boundary condition at the downstream end of Lower Spruce was specified. Normal Depth was chon with a slope of 0.0004 ft/ft. After the boundary condition was entered, the editor was clod and the flow data was saved as “10, 50, and 100 year flow events.”
