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WWRC 84-09
Design and Installation of a Weighing Lysimeter

Objectives

The purpose of this research was to develop and install an undisturbed weighing lysimeter in the Laramie River Basin. This location will facilitate providing the necessary management to insure continuous and reliable operation.

The lysimeter contains an undisturbed soil profile with accompanying vegetation. To the best knowledge of the authors, the lysimeter is the first system of its type installed anywhere, particularly at high elevations.

Once operational, the lysimeter will be used to:

  1. Provide the best direct estimate of water use by meadows in the Laramie area.
  2. Evaluate the role of rainfall in meeting plant water requirements.
  3. Provide comparative data to evaluate the accuracy of non-weighing lysimeters. Results will be used to correct errors or bias introduced into vegetative water use models through data obtained from non-weighing lysimeters.
The key to a successful weighing lysimeter is to design a system capable of detecting a change in weight equal to a millimeter of water when the lysimeter itself weighs several kilonewtons. For example, a precipitation event on the surface of a lysimeter equivalent to 1 mm of water may weigh approximately 10 Newtons. To detect a change in weight equivalent to 1 mm of water, the weighing system would have to be sensitive to approximately the O.1% level. In actual practice, the lysimeter weighing system should be sensitive to approximately 0.03%. This can be accomplished by making the top area of the lysimeter large relative to its depth, by maintaining the water table depth precisely and by using modern high technology sensors on the weighing system and a computer controlled data acquisition system.

84-09 Table of Contents
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