CHOKING IN WATER-SUPPLY STRUCTURES AND NATURAL CHANNELS

Techniques are presented to predict the choking phenomenon which occur s in natural and man made waterways with constriction features. The te chniques use the energy equation, the momentum principle, and the cont inuity equation in one dimensional flow derivation; both the form and the friction losses are considered in the study. The different loss co efficients assumed and introduced in the governing equations are extra cted and grouped in functional relationships to predict the choking oc currences. Governing equations are transformed to relate a threshold v alue of Froude number, termed as the limiting Froude number, to the ge ometry of the constriction feature and to the discharge coefficient fo r different flow regimes including subcritical and supercritical appro ach flow conditions. Governing flow equations in constricted channels result in a Froude number termed as the working Froude number. By comp aring the limiting and the working Froude numbers, occurrences of chok ing phenomenon can be predicted. Theoretical derivations are used in c onjunction with laboratory data for horizontal board constrictions to develop a more general coefficient of discharge applicable to severe c ontractions and to estimate the subcritical upstream flow conditions.