Optimal scheduling of maintenance dredging in a maritime transportation system

A maritime transportation system is a network of ports and commercial terminals connected by navigation channels and navigable inland rivers that enables international trade and the global supply chain. The channels and rivers are subject to recurring sedimentation, which reduces available depths, sailing drafts, and volumes of cargo that vessels can transport between ports. To maintain this network at sufficient depths and enable cost-effective maritime transportation, a specialized fleet of dredging vessels, or dredges, periodically remove accumulated sediment and restore capacity. Scheduling dredges to perform work requires simultaneous consideration of factors specific to the location, dredge, and underlying maritime network and, in practice, often results in significant inefficiencies and delays. Previous models proposed in the literature to optimize dredge scheduling are either intractable or consider only limited aspects of the problem. This paper defines the problem of tactical dredging portfolio scheduling, introduces the General Dredge Scheduling Model (GDSM) as a constraint programming model to solve this problem, and applies GDSM to a realistic problem composed of a portfolio of dredging jobs, fleet of dredges, and sets of seasonal and environmental restrictions.