Design Detention Pond

Design Detention Pond is a powerful stormwater model program that helps engineers analyze and design simple and complex watershed. This program lets you:

Analyze pre- and post-developed watershed conditions and pond sizes;
Analyze one watershed condition and pond sizes;
Use any rainfall duration or distribution to compute hydrographs;
Compute hydrographs for multiple events;
Automate almost every aspect of drainage design computations;
Build customized reports;

When you first run the command, the Select Carlson Pond File dialog box opens. You can start a completely new pond project or open an existing pond project.

Select Carlson Pond File

Pond Design Settings

When you start a new pond project, the pond design settings dialog will open first to let you set up the project watershed information, rainfall data, calculation method and report format. The Import button allows you to import the project settings from an existing pond project. The pre- and postdevelopment watershed surface files and layers files are imported too.

The general tab allows selection of the runoff hydrograph method, and setup of the hydrograph time span. There are SCS TR-20 method and Rational method for producing a runoff hydrograph for a given subcatchment.

Pond Design Settings

Subcatchment:

Subcatchment tab allow you to set up the watershed conditions for existing and proposed conditions. Check Single Watershed Condition box when designing a pond to hold all the runoff from the watershed. The watershed layer file is defined in the program of Define Watershed Layers. The Edit button can lead you to the program to make any changes. Please refer the Define Watershed Layers documentation to set up the watershed layers. Select SCS Unit Hydrograph, supported options Delmarva, SCS Curvlinear, and SCS Triangular. If SCS Triangular is selected the Peak Attenuation Factor may be set.

Rainfall:

The rainfall tab defines rainfall data for the SCS and Rational runoff methods. The storm type determines what the rainfall distribution is selected. The rain library button allows you to choose a storm type from the available rainfall distributions, and you can also create new rainfall data.

The AMC (Acedent Moisture Condition)specifies the moisture level in the ground immediately prior to the storm. Use a value of 2 for normal conditions.

In the rainfall event spreadsheet, you can specify various storm events and their total precipitation.

Report:

In report tab, you can select the report type: Carlson report or formatted report. The formatted report is display the report in a .pdf file format. The report scenario list allows you to report watershed runoff and pond sizes for multiple events.

Display:

In display tab, you can set up the pond storage units and subcatchment area units.

Pond Design

The pond design dialog opens when you start an existing pond project, or finish setting up the project settings for a new pond project. This dialog allows you to enter subcatchment parameters, and analyze the watershed runoff and pond sizes.

Subcatchment:

Subcatchment tab is where you enter the subcatchment data. The Update Subcatchment button allow the program to pull out the information from the existing and proposed watershed surface files and watershed layers files and fill all the values automatically. You can also enter values manually. The Edit buttons next to all the fields allow you to run the Curve Number program and Time of Concentration program to calculate the CN and Tc values. Please refer to the user manual on Curve Number command, and the Time of Concentration commands, both SCS method and Rational method.

When there's only one watershed condition in design, the target peakflow for outflow condition should be specified for pond sizing.

Pond:

Pond tab is where you specify the pond parameter and outlets information. The Stage-Storage Edit button opens the Input-Edit Stage-Storage dialog to create and edit the pond data. The Stage-Discharge Edit button opens the Multiple Outlet Design dialog to create and edit the outlet data. There are two methods to estimate the pond size: TR-55 method and Linear Storage method. Please refer to the user manual on the topics of Input-Edit Stage-Storage, Multiple Outlet Design, Detention Pond Sizing - TR-55 method and Linear Storage method.

Hydrograph:

When click on the Compute button, the results of all the rainfall events are shown on the Hydrograph tab. The peak flow results are shown in the spreadsheet, and the hydrograph of highlighted rainfall event are displayed on the top. The Pond Inflow hydrograph is the runoff hydrograph of proposed watershed, Pond Outflow hydrograph is the routing hydrograph, and the Target Outflow hydrograph is the runoff hydrograph of the existing watershed. When the routing hydrograph is less than the target outflow hydrograph, the project result passes.

Report

The Report button generates report of the watershed information, pond size and outlet parameters in detail. You can setup report settings on the dialog of Pond Design Settings.

When select the option to Report Input Data In Detail on the Subcatchment Report Setup dialog, the area, ground cover, and runoff coefficient for every subarea will be listed in the report; otherwise only the weighted runoff coefficient and the total area will be shown.

The Pond Report Setup dialog has the options to report pond data and outlet data in detail, and the options to draw the stage-storage curves, the stage-area curves, and the stage-discharge curves.

The Hyrograph Report Setup dialog provides the options to report hydrograph data at every time interval; and the options to draw runoff hydrograph and routing hydrograph.

Libraries

There are four hydrology libraries used in the program: Rational Rainfall Library, SCS Rainfall Library, Curve Number (CN) Library, and Drainage Runoff (CF) Library. Please refer to the user manual on those topics.

Prompts

Design Detention Pond dialog: Fill in values.

Pulldown Menu Location: Structure > Design Detention Pond
Keyboard Command: pond_design
Prerequisite: a pond file (.pond)