Hopper Overflow Management Tool
Type:
Presented during:
WODCON XXII - Enhance the Harmony between Dredging and Ecology
Authors:
S. Saremi and J.H. Jensen
Abstract
"The release of excess seawater in hoppers take place through the overflow arrangement. The overflow contains fine sediment, the amount of which depends on the type of sediment being dredged, the concentration of the dredged mixture being pumped into the hopper, dredging rate and the hopper configuration (planar area, and hopper shape). Depending on the type of dredging works and the environmental settings, the overflow will be managed against a set of targets on sediment spillage. Often, targets will be to minimize overflow spill to meet given environmental objectives as set out in approval conditions. In other cases, however, the target can be to harvest the courser fractions of the dredged material i.e. to wash out the fines; the objective being to retain high concentrations of the finer fractions in the overflow. In either case, managing the overflow remains a crucial element of an optimal loading operation and predictability of the overflow is key. The hopper sedimentation and overflow model developed by Jensen and Saremi (2014) calculates the hopper loading rate, bed level rise and the overflow losses with good degree of precision. The model is deterministic and based on a two-layer approach and provides valuable information regarding the time variations in bed level and overflow concentrations. In Jensen and Saremi (2014), the hopper shape was assumed to be rectangular. In the following, this shortcoming is revisited and the set of equations governing the two-layer system is generalized to take the hopper shape and therefore its impact on loading rates and overflow losses into account. Moreover, the model is now generalized to represent the constant tonnage system (CTS) rather than the constant volume system (CVS). With these extensions, the applicability of the model is broadened allowing it to serve as an overflow management tool in both planning and operational modes. Due to the computational swiftness of the model, predictions of the rate of bed level rise and the overflow losses can be derived on-the-fly. The swift computations can be used to support the management of the loading operations by adjusting dredge rates, overflow shaft elevation and inflow concentrations settings that ensure optimized loading rates and overflow targets are meet. "
Keywords: Dredging, Hopper shape, Overflow, Spill, Optimization, Spill management.