1. Background and Scope

Irrigation system deterioration can exist for years before becoming apparent to frequent users. However, an observer viewing an installation for the first time or infrequently may spot the deterioration immediately. Thus, water users and providers are often surprised to find that their water measurements are unacceptable because their system and measuring devices have deteriorated. Regular and careful inspections with the specific intent of finding deterioration in early stages will help prevent this unpleasant surprise. These inspections will also help reveal changing delivery needs that require other types of measuring devices and disclose other possible errors of operation. Another problem is that operators do not always know or use proper techniques to obtain accurate measurements. The best way to handle this problem is to provide good training.

This chapter shows water users and providers what to consider and check during system inspections to help maintain accurate water deliveries. Users can protect water rights and prevent overcharging by understanding these same considerations.

The performance of weirs and flumes will be used to illustrate flow and accuracy principles because irrigation operators will likely be more familiar with their use. Also, many of the factors which adversely affect accuracy are visible on these devices but are hidden in closed­conduit devices. Many of the factors and principles established for weirs and flumes also apply to other water­ measuring devices. These principles are elaborated upon in forthcoming sections concerning specific devices.