FMA Challenge 3: Difference between revisions
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This demo comprises the third and final model of the FMA Challenge series and assumes that you're an intermediate to advanced TUFLOW user. <br>
This challenge investigates a typical non-urban stream from the California Central Valley. The stream originates near the Sierra Nevada Foothills and conveys runoff to the West into the Central Valley Flood Management System. The streams are natural, with large amounts of conveyance in their upper reaches. As the streams progress downstream, their conveyance capacity gradually reduces. At some point nearing the valley floor,
From this challenge, it is expected you will develop skills in:<br>
*Understanding of the influence of levees on flood behaviour;
*Understanding of the influence of channel roughness on flood behaviour;
*Understanding of the influence of infiltration on flood behaviour;
*Nested 1D/2D models; and
*Understanding the Green and Ampt infiltration method and USDR soil types.<br>
*[https://www.tuflow.com/Download/TUFLOW/Demo_Models/FMA_Challenge_Model_3_QGIS.zip QGIS Data Download]
*[https://www.tuflow.com/Download/TUFLOW/Demo_Models/FMA_Challenge_Model_3_Mapinfo.zip MapInfo Data Download]
*[https://www.tuflow.com/Download/TUFLOW/Demo_Models/FMA_Challenge_Model_3_ArcGIS.zip ArcGIS Data Download]
=Relevant Tutorials=
Other tutorials that are relevant to this challenge that may help refresh your memory are as follows:<br>
*1D-2D Linking - <u>[[
*
*Running Scenarios - <u>[[Tutorial_M08|Tutorial Module 8]]</u>
*Running Events - <u>[[Tutorial_M09|Tutorial Module 09]]</u>
<br>
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Cell size selection is managed through the use of variables.
Within the river bed, 1D sections spacing
{| align="center" class="wikitable" width="50%"
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! style="background-color:#005581; font-weight:bold; color:white;"| Active 2D Cells
|-
| 100ft || 338,
|-
| 200ft || 84,
|}
All outflow from the model was assumed to be only via the main creek (ie. there was no water level boundary applied to the 2D overbank domain).▼
==Topography and Bed Resistance==
The provided DEM via GMG format was too coarse for hydraulic modeling as key hydraulic features (such as levee crests) were not adequately represented. The first step was therefore to process the 20Gb of LiDAR data into a higher resolution DEM. A 10ft DEM was created, a small part of which is illustrated below.
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To check these Manning's 'n' assumptions, a sensitivity testing was completed on the in-bank roughness and is detailed further in the following sections.
==Boundary Conditions==
The 1d/2d linking was along the top of the levee. The elevations along these levees were extracted from the 10ft DEM, these and other significant features were included in the TUFLOW model as 3D GIS breakline layers, ensuring the hydraulic control is represented in the grid regardless of cell size.▼
===Open Boundaries===
The flood extent from the 100ft 2D grid model is shown below.▼
A single hydrograph, derived from a previous hydrologic analysis was applied as a QT boundary via a 1d_bc.
▲All outflow from the model was assumed to be only via the main
===1D/2D Linking===
▲The
=Results - No Infiltration=
▲The flood extent from the 100ft 2D grid model with no infiltration and Manning's 'n' within the channel of 0.2 is shown below.
[[File:FMA3_3.jpg|600px]]
==Levee Overtopping Assessment==
===Sensitivity Creek Manning's n Test (Scenario 100ft n0.1)▼
To assess the timing and location of where levee banks were overtopped, the TGC was setup with the evacuation route command:<br> <font color="blue"><tt>Read GIS Z Shape Route </tt></font> <font color="red"><tt>==</tt></font> shp\2d_zshr_T3_levees_001_L.shp | shp\2d_zsh_T3_levees_001_P.shp.<br>
As discussed in the Manning’s n table above, the main creek n value of 0.20 is considered very high, especially in the lower reaches of the study area. A sensitivity analysis was carried out by lowering all the Manning’s n values in the main channel (modeled as 1D cross-sections) to 0.10. ▼
Via review of the RC Map Output Data Type and the _RCP output point layer we can identify sections of the levee where a breach has occured (refer below).<br>
[[File:FMA3_6.jpg|600px]]▼
▲As discussed in the Manning’s n table above, the main creek n value of 0.20 is considered very high, especially in the lower reaches of the study area. A sensitivity analysis was carried out by lowering all the Manning’s n values in the main channel (
The image below shows the flood depths and extent
[[File:FMA3_3.jpg|600px]][[File:FMA3_4.jpg|600px]]<br>▼
The effect of channel roughness can also be seen in hydrograph outflows from the model downstream boundary (refer figure below).
▲[[File:FMA3_4.jpg|600px]]
Of particular interest is that reducing the n value to 0.1 has a significant effect on the arrival time of the flood waters at the model outlet (much earlier), and reduces the volume of water flowing onto the floodplain by around 20% due to the higher conveyance of the creek. Also of interest is that for the n=0.2 scenario, some overbank floodwaters return to the main creek near the model outlet causing a delayed second rise in the outlet flow hydrographs as illustrated in the chart further below. This effect does not occur for the n=0.1 scenario, with all overbank floodwaters remaining on the floodplain.<br>
Please note the scenarios provided in the legend below are as follows:<br>
*100ft = 100ft cell resolution, no infiltration and channel roughness of 'n' = 0.2<br>
*200ft = 200ft cell resolution, no infiltration and channel roughness of 'n' = 0.2<br>
*100ft (n0.1) = 100ft cell resolution, no infiltration and channel roughness of 'n' = 0.1<br>
*100ft GA = 100ft cell resolution, Green and Ampt infiltration with channel roughness of 'n' = 0.2<br>
*Inflow = Hydrograph input at northeastern QT boundary.<br>
[[File:FMA3_5.jpg|600px]]
=Green and Ampt Infiltration Setup=
▲[[File:FMA3_6.jpg|600px]]
▲The soils layers provided were roughly classified into two soil types for the purposes of demonstrating the Green-Ampt infiltration feature in TUFLOW. The soils are shown in the image below where:
<ol>
<li>Red indicates a Sandy Loam.
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[[File:FMA3_7.jpg|600px]]
The 100ft and 200ft simulations were re-run with
The mass balance reporting from TUFLOW indicates over half (58%) of the water infiltrates into the ground during the 171 hour simulation. For the flow out of the model see “100ft GA” in the chart of flow out of the model presented in Challenge 3.▼
▲The mass balance reporting from TUFLOW indicates over half (58%) of the water infiltrates into the ground during the 171 hour simulation.
[[File:FMA3_8.jpg|600px]]▼
▲[[File:FMA3_3.jpg|600px]][[File:FMA3_8.jpg|600px]]
=Conclusion=
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In this challenge, we explored typical non-urban stream of the California Central Valley, with scenarios of various infiltration and flood levees adopted. From this, we gained a better understanding of the influence of flood levees on surface water behaviour, understanding of the Green Ampt infiltration method and USDR soil types, and a better understanding of nested 1D/2D models.
Congratulations on finishing
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