- Dredging -- Lower Columbia River Watershed (Or. and Wash.),
- City planning -- Oregon -- Portland,
- Traffic monitoring -- United States -- Oregon
About $15 billion of freight passes annually through the Lower Columbia River (LCR) navigation channel to reach Portland and Vancouver, where most of it connects with land transport. This commerce plays a vital role in sustaining the regional economy and connecting Oregon to the global economy. The timely connection of truck and rail transport with vessels is vital, especially for export traffic. This link is susceptible to disruption if water depths in the navigation channel are shallower than expected, leading to delays and/or draft limitations. Moreover, ship drafts have increased in recent decades, 25% of the vessels calling in the river sail with a draft close to the channel depth at low water, and these carry roughly 70% of the cargo. A large vessel may have as little as 0.6 m bed clearance when it passes through a low-tide point in the river, which each vessel in transit must do. Thus, prediction and real-time communication of water level to vessels is vital to safety as well as efficiency. This has been implemented through the LOADMAX system, consisting of telemetered water-level gauges and a forecast model. Moreover, the dilemma has been made more critical by changes in the river – low water levels in the river channel between Wauna and Vancouver have decreased 0.3-1.2 m since 1940. The rate of decrease depends on location and riverflow, but appears to have accelerated in the last decade. The reasons for this decrease are not understood. For perspective, an ongoing 0.9 m channel deepening will cost about $150 million when completed, so unintended decreases in water depths are expensive as well as potentially dangerous. Lower water levels in the river also increase carbon emissions, because smaller loads mean more land and vessel transport trips. Further, navigation and salmon habitat restoration are closely connected. Dredging is used to maintain the channel, and habitat restoration is an integral part of the channel deepening. New dredging strategies are needed to maintain the newly deepened channel, but dredging that removes material permanently from the river may, further lower water levels, limiting possibilities for habitat restoration and reducing bed clearance for large ships. These problems will be exacerbated by future decreases in summer river flows due to climate change.