Investigating the Effects of Hydrographic Survey Uncertainty on Dredge Quantity Estimation

Abstract

Quantity estimation is a critical issue in dredging projects since it has a direct impact on the project process and cost. Hydrographic surveying is the main tool for measuring the horizontal coordinates and elevation of the sea bed and subsequently quantity estimation. In the present work, data from different dredging projects in Egypt have been utilized with Monte Carlo simulation to investigate the effects of the hydrographic survey uncertainty on the estimated dredge quantities. Results showed that the horizontal position uncertainty significantly affects the estimated dredged volume uncertainty especially in irregular bed's areas. Consequently, the conventional low-cost, low accuracy positioning devices (e.g., DGPS) may increase the cost of dredging. Therefore, more accurate high-cost devices (e.g., RTK GPS) could be recommended to reduce the costs of the dredging projects. The results showed also that uncertainty of measured bed levels have a direct impact on the estimated volume. Hence, the effect of tide correction techniques is studied and an alternative approach for dredged volume estimation is proposed to avoid the uncertainty in measuring the tide. In this approach, the measured depths are referenced to the ellipsoidal geodetic datum rather than the chart datum.