FMA Challenge 1 (1D-2D linked)

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Introduction

If you haven't already completed the tutorial models, please see this tutorial model page. This page is for TUFLOW users of intermediate to advanced caliber.

In this challenge, a fully two-dimensional model with a nested one dimensional model will be developed to explore an Urban Riverine conditions with an urbanized over-bank floodplain. The model includes several hydraulic structures/bridges within the main stream system which will impact flood elevations. Flooding within the urbanized over-bank floodplain is expected.


From this challenge, it is expected the user will develop their skills in:

  • Nested 1D/2D models;
  • Understanding Urban Riverine conditions and over-bank floodplains,
  • Understanding of the influence of hydraulic structures;
  • Using scenarios and variables to determine a suitable cell size, timestep and log output scenarios; and
  • Using bc layers with HX, XP, CD and CN types altogether.

Data for this model is provided via ZIP compressed file posted on the internet/FTP for download.


Data Notes

The original data for this analysis has been modified from its original datum and original elevations have been altered and corrupted such that the data would not be usable for real world modeling, analysis and mapping. Datum data has been stripped from the files provided. A combination of statute (ft) and metric (m) data is provided in the challenge data. Analysis may be performed in metric or Statute units, however all returned data shall be delivered to FMA in Statute (ft) units. Additionally, some of the provided data indicates vertical Datums 29 and 88. We have verified all data provided is in the same vertical datum and for this model challenge assume that is the vertical datum “FMA 12”.


Information to Modelers

Assignment of all parameters for this analysis are at the discretion of the modeler. A high resolution aerial image is provided so that land cover details can be inspected. The following information is provided for guidance:

  • Several stream photographs and structure photographs are available in the data. Several data sets are also provided to assist the modeler in determining model parameters.
  • A starting set of overland N-Values is provided in the land use data set, however, the modeler can modify these as needed.
  • Terrain data is provided in elevation contours. Depending on the system the modeler will use to create terrain data for their model, the modelers may need to add supplemental break line data to these contours to obtain a more accurate model in the over-bank floodplain, which demonstrates valid flow and storage paths/volumes.
  • The modeler is to assume that the terrain data provided represents the ground conditions at the time the runoff event occurs, and that the ground conditions will not change during the event. Terrain data is provided in DEM data file formats.
  • The Inflow Hydrograph for the main stream and tributary are provided in the EXCEL spreadsheet contained in the INFLOWS directory. The inflows are referenced to CHAINAGE locations along the creek (matching survey cross section CHAINAGE).
  • Previous studies indicate that backwater conditions at the mouth of the discharge of this stream into the larger downstream river do not extend more than a couple hundred feet into this stream. For the purposes of this model, assume the stream freely discharges into the downstream river.
  • There are no accredited levees within the model domain.
  • In the case that standards and specifications need to be referenced, please refer to FEMA guidelines, assuming the event described in this challenge represents the 100-year event. (Except, you are not limited by FEMA’s approved software list, and may use any software you have available for the numerical analysis of this Challenge)
  • Depth grids should be developed based on the provided Appendix N - Flood Risk Data Development and Analysis (Public Review).pdf guidelines. The modeler will need to determine an appropriate grid size.

The model can be constructed as follows;


GIS Inputs

We have provided the location of the proposed study in the FMA data under FMA_Data\FMA_01\. Two GIS layers have been provided, Fill_Area and Cut_Area. For this impact assessment the fill area is to be removed from the floodplain for the 100 year Average Recurrence Interval (ARI) event being modelled. The cut area will have 1 m removed from the existing ground surface to increase the conveyance in the area. To make the GIS changes, please select your GIS package from the list below:


Control File

To refresh the user's mind, there are two methods for running multiple scenarios in TUFLOW:

  • Create separate control files for each simulation; or
  • Run multiple simulations from the same control file (.tcf) using simple logic statements.

It is up to the user to decide on which method to use.

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