Scaling the solute transport characteristics of a surcharged manhole

Abstract

Guymer et al. (2005) presented the results of experimental work that explored the effects of diameter and surcharge on the solute transport processes occurring in surcharged manholes. A threshold surcharge level was identified, with two contrasting hydraulic regimes being observed at surcharge depths above and below the threshold value. In this study, a 1:3.67 physical scale model of an 800 mm diameter manhole has been built to investigate the effects of scale on hydraulic and solute transport characteristics. Dye tracing experiments and energy loss measurements have been made in the physical scale model. The results suggest that geometric scaling laws may be used to characterise the flow regime, and to identify the threshold surcharge depth. Solute transport characteristics are presented in the form of a cumulative residence time distribution (CRTD), in which the x-axis (time dimension) is normalised by the nominal residence time (volume/discharge). The CRTDs reveal the effect of hydraulic regime on solute transport processes, with two distinct characteristic curve shapes corresponding to the two contrasting hydraulic regimes. A preliminary comparison of the normalised CRTD curves for the model and prototype systems suggests that the scale-independent solute transport characteristics of the structure may be characterised by just two dimensionless CRTDs; one for pre-threshold and the second for post-threshold hydraulic conditions.

Keywords:

• dispersion
• energy loss
• hydraulic regime
• manhole
• cumulative residence time distribution (CRTD)
• sewer, solute transport
• surcharge