Drainage Design Exercise. Computer-based Subsurface Design

Transcription

1 Drainage Design Exercise Computer-based Subsurface Design OBJECTIVES Introduction of the LANDRAIN software: a program for subsurface drainage design. During last year's cropping season, a farmer, Mr. Igro Mograin, experienced crop production loss due to waterlogging. You have been provided with a contour map of his field (Figure 1) and are required to provide an efficient subsurface drainage system. PROCEDURE Copying files to your working directory Copy the Landrain directory to your flash drive or to the T drive. Do not attempt to work from the network drive. Find and double click the Landrain.exe icon. The main menu of LANDRAIN will be displayed. Setting the working directory Select Setup Option from the main menu to define the data directory. Set the data directory as t:\landrain\workshop. Without defining the data directory the program will be unable to load the data file.

2 Data Transfer When you select this command, you will be asked to specify input and output file names. The output filed will be saved in LANDRAIN format with the file extension,.mdl. The input file should have one of the following 4 formats: 1. Point Number, X-distance, Y-distance, Elevation (#,x,y,z) 2. Point number, Northing, Easting, Elevation (#,y,x,z) 3. X-distance, Y-distance, Elevation (x,y,z) 4. Northing, Easting, Elevation (y,x,z) The sample input file (design.dat) has the third format. Edit Data This option allows you to edit, create and examine the input data file. Before editing this file, display the map to locate the areas requiring editing. Loading the data file Once you have specified the input file, you can view a contour map of the data. If there are errors in the input file, an error message will be displayed. Errors can be corrected by returning to the edit menu. You can reload the data file by entering the file name All the existing files on a disk drive can be displayed by entering *.* in place of the file name file name. Loading the boundary file Select the option for loading a boundary file. The boundary file for this exercise is design.bdr Specify the format of the boundary file, in this case; B. Triangulation After loading the file, triangulation must be performed. Without triangulation, no further processing of the data file is possible. Changing pipe size Before, designing the layout of subsurface drainage system, it is necessary to check the pipe sizes available from local

3 suppliers. In this instance assume that you can get any pipe size required. Select the set options from the main menu and then select I. There are 11 different default sizes. You can add or delete the pipe sizes that you need to use for laterals or mains. Some contractors in Illinois use 3-inch pipe. Pipe Size Installed Cost* (in) ($/ft) * Feel free to use costs from your friendly neighborhood contractor Designing Subsurface Drainage Select the drainage editor from the main menu. The contour map will be displayed. Beside the contour map, a sub-menu will be displayed. Select the A option to add a new node. You can specify the inflow and pipe type (lateral or main). You can always use the Edit option to switch between pipe types. In LANDRAIN, mains a non-perforated and will have no flow unless laterals are connected to them.

4 Install a main that runs along the right edge of the field from (995, 5) to (995, 945). Press ESC to get back to the main drain layout screen. You can add a lateral to the main by inserting a node at a suitable location and adding an end node at the other end of the lateral. Always press ESC to get back to the main drain layout screen to add a new lateral. Equally spaced laterals can be installed by using the Begin Automatic Laterals option from the Add submenu. Continue laying out the drainage system. Be careful in selecting the parameters for design and location of tile lines (lateral, main) and the outlet. After completing the layout, use the Intersect option to incorporate the topography into the drainage layout, and the Bury option to bury the tile lines. The system should be buried between 3.5 ft. and 4 ft deep. Lateral sections that are outside of the specified buried depth range as colored red or purple. Carry out an on-screen analysis to rectify any error encountered during the burying process of program. If any problems are encountered during the burying process, they can be rectified using the Profile command. This option will allow you to move any tile line that is laying above on the surface or that is not within defined minimum and maximum burial depth. To execute the profile command, move the cross bar to the beginning of the tile line in question, select the Profile command, and then move the cross bar to the end of the tile line. Press E and wait. After a while the complete profile of the selected tile line will be displayed. Now you can make changes to the tile line layout. Note: After each modification to the drainage network, save it!! Flow Calculation Bring the cursor at the outlet and invoke the FLOW command, the flow will be calculate using the Manning equation and based upon different pipe sizes. If you have changed the pipe size, make sure that you also change the roughness coefficient for that particular pipe size. Output Printout Select the printer option from the set option menu. You will learn about the various options during the exercise. Assignment In a report, provide Mr. Mograin with information that he can use to make decisions about the suitability of a drainage system. This report should include, inter alia, A contour map of the field, and a table with the area (acres and percent) between successive 1 ft contours. For drain spacing ranging from 40 to 120 ft, the per acre cost of installing the drainage system, and the break-even income based on a system life of 50 years and suitable interest and marginal tax rates. Maps of the system layouts for 100 and 50 ft drain spacing. The layout, cost, and break-even income for an 80-ft spaced system with two control zones, one at the outlet (995,5) and the other near the north east corner of the farmstead (200,240). Control structure costs can be found at the Web site shown below. This does not constitute an endorsement for the product. You may choose to use structures from any manufacturer as long as you include the source of the price quote. Other information that you deem necessary. You are the engineer. Express yourself!

5 Figure 1. Elevation map of plot to be drained