Concrete block weir and orifice discharge characteristics for stormwater detention outlet control

A series of twelve (12) full-scale laboratory tests was conducted to evaluate the performance and hydraulic characteristics of various orifice and weir configurations commonly used In single- and multiple-stage stormwater detention outlet control structures constructed of concrete block. The use of such concrete block structures In conjunction with detention storage appears to be growing because of apparent practical, economic, and esthetic advantages over other types of structures. However, lack of published orifice and weir discharge coefficient data for openings formed from concrete blocks leaves the hydraulic engineer with little choice but to design the detention storage and outlet control opening(s) using "guesstimate" coefficients. Inaccurate coefficients could result In either expensive over-designed or Ineffective under-designed ponds. Several combinations of weir and orifice opening geometries were tested and evaluated to account for pond bottom effect, "stacked-weir" arrangement, multiple orifices, and combined weir and orifice configurations. This thesis presents the results of a series of twelve (12) tests, which relate discharge coefficient to orifice and weir configurations and heads. It also demonstrates that required (design) detention storage will vary significantly within a relatively small range of assumed outlet weir and orifice discharge coefficients. The sensitivity analysis between required detention storage and assumed weir/orifice discharge coefficients was performed using common HEC-1 and TR-55 routing procedures. Recommendations are presented for hydraulic design, construction, and maintenance of concrete block stormwater control structures.