Wednesday, March 3, 2010

Drainage Areas

Tonight I was thinking of a way to increase productivity when creating drainage area maps. Drainage area maps are pretty simple to produce. The plan is basically contours, drainage areas, flow arrows and a drainage table. Using parcels can be a great way to create drainage areas.  So I decided to create a simple parcel style that would automatically display the drainage area ID,  acreage and runoff Q. This label style would save me time from creating small blocks or text to identify drainage areas.

The first step is to create two simple expressions under my Parcel/label styles/area. My first expression was for my pre-development areas (existing drainage area map). I used a runoff coefficient of 0.30 and the Town of Flowermound 100 year rainfall intensity of 8.82. Then  I created a post-development expression (proposed drainage areas) with a runoff coefficient of 0.90 and rainfall intensity of 8.82.

Next I created two new label style under Parcel Label Styles/Area Style called DA-PRE and DA-POST. In my new label styles I added the new expression that we just created into the proper label styles. Then I turned on the boundary option in the styles and used a circle. And that’s basically it. See my images below for examples. Hopefully this will give your more ideas with using expressions. Later



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  1. If you are looking at ways to increase productivity for drainage area analysis look into Map Topologies. There is some pretty amazing stuff you can so with Topologies and a slick Excel spreadsheet.

  2. Good post. I like to create User-Defined Property Classifications for parcels. This way, I can keep the label somewhat dynamic in the sense that I can modify the values through the Parcel Properties dialog box and have the label update accordingly. For instance, I can define properties like the CN and rainfall, etc., and just have one label that incorporates those variables. It saves me the little time it would take to revise the expression each time I needed to adjust a variable like the CN.

  3. thanks for the comments guys. I will have to try the topology and the user defined property classifications parcels

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