A new pocket-sized drainage calculator available from the University of Minnesota (U of M) extension service puts agricultural drainage calculations in an easy-to-use format.

Gary Sands, engineer with the U of M extension service, developed the new calculator. It will be a handy tool for farmers, drainage contractors, engineers, public agencies, crop consultants, extension educators and water quality professionals across the Midwest region.

Drainage calculations and other information appear in a "slide chart" format. Calculations are made by sliding an inner sleeve to match points on the outer jacket. Instructions for use are included on the calculator.

Side one of the calculator allows users to compute the required pipe size for various pipe grades and drained acres. The reverse calculation, from pipe size/grade to drained acres, can also be performed.

The calculator can be used for both corrugated and smooth-interior pipe. Tables are also included on side one for selecting drainage coefficients and estimating drainage pipe coil lengths based on the number of wraps on a pipe spool.

Side two of the calculator lets users determine flow rate and check to make sure minimum recommended flow velocities can be achieved. Feet of fall (elevation change) can be determined based on percent grade and length of run.

Other tables on side two include estimates of pipe requirements based on drain spacing and minimum recommended grades for various drainage pipe sizes and materials.

The pocket slide chart was developed in partnership with Prinsco, Inc. It may be purchased from the extension service distribution center for a nominal fee. Call 612-624-4900 or 800-876-8636 and ask for item number 07688.