Transcript Example8

Example 8
Multiple Rain Gages and
Weighting in HEC-HMS
Purpose
• Illustrate the steps to use multiple rainfall
gages on a watershed.
– Multiple gage inputs to a sub-basin
– Input weighted by gage weights, in the
example determined by Theissen polygons.
Learning Objectives
• Reinforce use of HEC-HMS Graphical
User Interface.
– Reinforce the concepts of “Projects” as a
data-storage paradigm.
• Explore different meterological model
concepts:
– Initial loss and constant rate loss model
– SCS Unit Hydrograph transformation model
– User-specified hyetograph.
Problem Statement
• Simulate the response of the Ash Creek
watershed at Highland Road for a 5-year
for the May 1978 storm using the two
recording rain gages as the input.
– Treat the entire watershed as a single subbasin.
– Each gage contribution is proportional to their
Theissen weights (determined elsewhere)
Example 8 Multiple Rain Gages
• Ash Creek Example 3
– Import basin model
– Import meteorological model
– Import time series model
– Verify run, then save.
Example 8 Multiple Rain Gages
• Verify run, then save
Example 8 Multiple Rain Gages
• Examine the rainfall
source file
– Two gages
• 14-W
• 15-W
– Theissen weights are
unreported
• 14-W = 0.12
• 15-W = 0.88
should work for this
example
Example 8 Multiple Rain Gages
• Create two gages in
Time Series manager
– 14W
– 15W
Example 8 Multiple Rain Gages
• Copy the date from
the external file
(Excel) into the
respective gages.
• Pay attention to nonuniform time, use the
fill feature as needed
Use chart to look for gaps in input
Example 8 Multiple Rain Gages
• Once gage data is entered, save.
• Meteorological model is next, we need to change
the model to allow multiple gages.
Select “Gage Weights”
Example 8 Multiple Rain Gages
• Select which gages will be applied to Subbasin-1
Example 8 Multiple Rain Gages
• Select which gages will be applied to Subbasin-1
Example 8 Multiple Rain Gages
• Enter gage weights – in this case depth weights
– Time weights are set to 1.0
Example 8 Multiple Rain Gages
• Run the model and examine output
Example 8 Summary
• Illustrate how to use multiple gage data and
assign by weights each gages contribution to
rainfall on a sub-basin.
– Example can be extended to multiple sub-basins.
– Gages need not be physically present on the
watershed, but should be close by (same
hemisphere?)
• More exotic approaches are mentioned in
Chapter 11, HEC-HMS user manual.
– Weighting methods require external data preparation
and weight determination