CEG 795 – Water Resources Modeling and GIS

Spring 2006

Exercise #7 (Additional Material)

Due: Monday, April 3rd

Utilize your base model from Exercise 6 to perform the following modifications.

Part I: Changing Manning’s n

  1. Use the base model from Exercise 6 and modify the model such that the channel is lined with an n=0.015 and the overbanks are graded earth (n=0.025).
  2. Import this new model into HEC-RAS and run for a scenario where the flowrate is 5000 cfs.
  3. Export the RAS model back to HEC Geo-RAS for floodplain/flood depth mapping.
  4. Prepare figures that compare the floodplain for the base scenario (Exercise 6) and the new scenario with different n values.
  5. Provide a brief discussion on how modifying the n values changed the model output.

Part II: Ineffective Flow Areas

  1. Use the base model from Exercise 6 and draw in a hypothetical roadway that crosses the river. Upstream and downstream of the roadway, define ineffective flow areas due to channel contraction and expansion.
  2. Import this new model into HEC-RAS and run for a scenario where the flowrate is 5000 cfs.
  3. Export the RAS model back to HEC Geo-RAS for floodplain/flood depth mapping.
  4. Prepare figures that compare the floodplain for the base scenario (Exercise 6) and the new scenario with ineffective flow area.
  5. Provide a brief discussion on how the identification of ineffective flow areas changed the model output.

Part III: Levees

  1. Use the base model from Exercise 6 and create levees on both side of the river that are at least 1000 feet long. The levees should be approximately 5 feet above the existing ground.
  2. Import this new model into HEC-RAS and run for a scenario where the flowrate is 5000 cfs.
  3. In HEC-RAS, determine if any of the levees were overtopped, if NOT, then increase the flowrate until some of the levees are overtopped.
  4. Once this new flowrate is determined, run HEC-RAS for two profiles (5000 cfs and ???? cfs depending on your situation).
  5. Export the RAS model back to HEC Geo-RAS for floodplain/flood depth mapping.
  6. Prepare figures and tables that compare the floodplain for the base scenario (Exercise 6) with that of the case with levees and the two flow rates.
  7. Determine how much (area) of the floodplain was reduced for the 5000 cfs case due to the levees.
  8. Provide a brief discussion impact of levees and how the overtopping was modeled.

Part IV: Blocked Obstruction

  1. Use the base model from Exercise 6 and create a scenario where a land development is going to occur adjacent to the river. The development should have at least 500 feet bordering the river.
  2. Based on your earlier analysis, determine how high the development should be for the Q = 5000 cfs case. Use a slightly higher elevation as your preliminary elevation for the development.
  3. Represent the development in HEC Geo-RAS as a blocked obstruction.
  4. Import this new model into HEC-RAS and run for a scenario where the flowrate is 5000 cfs.
  5. Evaluate whether your development is high enough from the new water surface. If needed, increase the height of your development and rerun.
  6. Export the RAS model back to HEC Geo-RAS for floodplain/flood depth mapping.
  7. Determine how much of the flood depths changed from the base case of no development. Provide a map and a table for this comparison.
  8. Provide a brief discussion impact of the development.

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