Evaluating Precipitation Options in HEC-HMS

Dr. Nelson


At this stage you have learned the basic modeling techniques in HMS. Now we will be dealing with the individual component of the modeling in greater detail. We will begin with the precipitation and we will analyze how different spatial and temporal precipitation models can be used, and the way HMS responds to all of them.

Our sensitivity studies will center around the Judy's Branch Watershed and you can use the same data as you did previously. We will use different precipitation methods as input and see how the output varies. You will perform the similar analysis with GSSHA (in the next assignment) and at the end you will compare the response of both HMS and GSSHA to different precipitation methods.

There are four rain gauge stations close to Judy's Branch Watershed namely Belleville Siu Research, Carlinville 2, Carlyle Reservoir and St Louis Airport. the first three stations are in Illinois and last one is in Missouri.


Belleville Siu Research

Carlinville 2

Carlyle Reservoir

St Louis Airport
















Observing Site

Belleville Siu Research, IL

Carlinville 2, IL

Carlyle Reservoir, IL

StL, Mo

To get the frequency storm data, you need to go to NOAA Atlas 14 website. Then, select the state by clicking on the map. You can then choose the station name (Observing Site, see table above) by selecting from the drop down box. See the following Figure:

To get Daily and Hourly data, you can go to this NOAA page and download the data as *.pdf files. For this assignment we have compiled data from some "interesting" storms and prepared a spreadsheet with the data. 


Go through following outlines of the assignment and try to understand the big picture of what you are going to do. Then go on to complete the Assignment

1. Basic Model set up:

2. Precipitation Set up:

Here we will use various rainfall types (we are not going to analyze the snowmelt processes, so the term precipitation here will represent only the rainfall). We will be using the following rainfall methods.

To Examine Spatial Variation:

In order to use the Thiessen Polygon method in WMS:


Examining Temporal Variations:

The temporal variation shows how the storm intensity changes over time, and the duration of the storm. For example if we know that a rainfall depth of 5 inches occurred in Belleville station between 5:00 AM and 7:00 AM, then the temporal distribution shows how the rainfall of 5 inches is distributed over the storm duration of 2 hours (5 am to 7am). This is an example of a 120 minute duration storm. On the other hand, the standard temporal distributions like Type I or II etc, distribute the rainfall over a period of 24 hours at an interval of 6 minutes.

The following temporal distributions will be analyzed:


Perform a single basin HMS analysis using following combinations of precipitation methods.

To turn in Now:

To turn in with the Precipitation Review Assignment (but be thinking about it now):