EXCESS DREDGING: IMPLICATIONS FOR NEGOTIATING ENVIRONMENTAL DOCUMENTS

摘要

The USACE has long recognized in its development of technical guidance documents and regulations for channel design, dredging operations and contracting that there are inherent excavation accuracy limitations in the dredging process. As a result of dredging equipment capabilities and limitation, excess dredging will occur below the allowable overdepth within the context of the current standard of 1 to 2 foot allowable overdepth. The extent of excess dredging is influenced by the dredging equipment, as well as the physical characteristics of the material to be dredged (new work vs maintenance), the project physical conditions (tides, currents, waves, debris), channel design (water depth), and operator skill. Further the measurement precision of bathymetric surveys complicates defining the extent of any dredging in excess of the environmental documents and permits.The primary purpose of this paper is to provide the dredging project manager seeking a dredging permit technical information and possible language to assist in negotiating a permit that is within dredging equipment capabilities. The use of the contractual definition of allowable overdepth as the permitted dredging limit often results in a permit requirement that is impossible for standard dredging equipment to meet. It can also impose an additional financial burden on the project that is not justified based on the related environmental impacts.The suggested remedy to avoid problems of permit compliance, and excessive overdredgmg is to accept the fact of dredging depth accuracy (or inaccuracy) in both the permit and the dredging contract. The permit language can then be crafted to limit excess dredging to isolated, small areas. There is the need to develop permit language that addresses the regulatory concern(s), yet allows areas of excess dredging that will occur from a combination of equipment characteristics, operator skill and project physical conditions. To meet these goals, the allowable overdepth for permit compliance (as reflected in the final project survey) could be measured in one or a combination of the following ways (excluding side slopes):1. Limiting excess dredging based on volume, either as a percentage of the total project or as a percentage of the allowable overdepth not dredged.2. Limiting excess dredging based on area, as a percentage of the total project area, excluding slopes.3. Limiting excess dredging based on average depth, weighted by area.