21.1 INTRODUCTION

Experienced water providers and users can use this chapter as a quick review of hydraulic principles related to water measurement and its relation to hydraulic design for environmental considerations.

The hydraulic design of flow measuring structures usually confronts the engineer with two opportunities. One is the design of measurement structures in a retrofit situation and the other is in original project design. The retrofit mode is usually difficult and requires much innovation just to obtain passable function within the space and sizing limitations and other constraints usually imposed. Because of the increasing emphasis on quantifying flow rates and volumes in most aspects of water resource planning and management, the retrofit applications currently dominate the design problems.

Most textbooks deal with recommending ideal installation situations and retrofit projects appear to be unable to comply without great economic impact. This too frequently can lead to arbitrary compromises that produce poor measurement performance. Even new installations may be limited by space requirements. This may force design decisions into the final construction that compromise accuracy. This chapter will strive to show the design concepts available, particularly those useful for designing both new and retrofit installations, and will point out measurement behaviors to be expected from various compromises. This chapter suggests those deviations that cause least impact and guides the designer to choices that may be hydraulically acceptable and still meet...