Model study of an outlet control structure used in wetland management

Abstract

Ducks Unlimited Canada uses o u t l e t c o n t r o l s t r u c t u r e s to create and manage waterfowl habitat i n New Brunswick. An o u t l e t control structure i s a hybrid hydraulic s t r u c t u re c o n s i s t i n g of four adjustable weirs mated to a corrugated metal culvert w i t h a p r e f a b r i c a t e d r e i n f o r c e d concrete box. The hydraulic operating c h a r a c t e r i s t i c s of these o u t l et c o n t r o l structures were studied through three approaches. F i e l d v i s i t s were made to three prototype structures and measurements of operational parameters were made. A one-sixth scale physical model of the f o u r - f o o t culvert diameter s t r u c t u r e was constructed and t e s t e d . A numerical model using e x i s t i n g weir and c u l v e r t theory was devised and r u n . The above three methods y i e l d e d three sets of r a t i n g curves ( r e s e r v o i r elevation versus discharge through the h y b r id s t r u c t u r e ) . These r a t i n g curves were compared t o each other and to the Ducks Unlimited design curve. The prototype observations, physical model, and numerical model r e s u l t s agreed very w e l l . These three also coincided w i t h the Ducks Unlimited design curve at low discharge rates, but the p h y s i c a l and numerical models both p r e d i c t higher discharges for a given head than the design curve at high discharge rates. E f f o r t s were made to i n v e s t i g a t e methods to f u r t h er increase the discharge through the s t r u c t u r e f o r a given head on the weirs, but more experimentation i s recommended.