Laboratory evaluations and field results are presented for a slotted weir used to measure discharge from subsurface drains. The head–discharge curve for the vertical slot is a simple power function with an exponent of 1.5. There was excellent agreement (r2 > 0.99 and 1:1 slope) between predicted and observed discharge in laboratory testing of 12 test weirs representing five slot widths. The primary advantages of the vertical slot weir are its simplicity, ease of maintenance, and ability to measure small flow rates. Disadvantages include a tendency for the slot to close a small amount over time as a result of creep when using a PVC pipe and the possibility for material to become clogged in the slot. The use of a spacer in the slot eliminated the tendency for the slot to close.

Document Type


Publication Date


Notes/Citation Information

Published in Applied Engineering in Agriculture, v. 17, issue 6, p. 783-786.

© 2001 American Society of Agricultural Engineers

The copyright holder has granted the permission for posting the article here.

Digital Object Identifier (DOI)


Related Content

The information reported in this article (No. 01–05–38) is part of a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director.