Tracer studies of a gravel bed wetland

• Published in: Water Science & Technology Vol. 34; no. 3-4; pp. 421 - 425
• Main Authors: Shilton, Andy N., Prasad, Julius N.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: London Elsevier Ltd 1996; IWA Publishing
• Subjects: Design; Gravel; Hydraulic retention time; Hydraulics; Influents; Inlets (waterways); Intake manifolds; Longitudinal dispersion; Plug flow; Plug flow chemical reactors; Retention; Retention time; Storm seepage; tracer; Tracers; Wetland; Wetlands; hydraulic retention time; Wetland; tracer
• ISBN: 9780080430867; 0080430864
• ISSN: 0273-1223; 1996-9732
• DOI: 10.1016/0273-1223(96)00607-5

Current rational design methods for subsurface flow wetlands idealise these systems as plug flow reactors. This assumption ignores the existence of longitudinal dispersion, short-circuiting, stagnant zones and so on. This paper reports on a series of three tracer experiments performed on a gravel bed wetland with a design hydraulic retention time of four days in order to study its hydraulic characteristics. The results present the hydraulic retention time distributions. The first tracer run using a single point inlet source had a mean time of 2.71 days. The second and third had the influent distributed across their width using an inlet manifold and yielded mean retention times of 3.47 and 3.41 days respectively. Further interpretation of these results indicates that the current plug flow assumption used in design can result in over estimation of treatment efficiency.