Pumps to Save Water at Navigation Locks
The practice of using navigation locks along inland waterways dates back to Ancient Egypt where seasonal navigation locks allowed vessels to sail between the Red Sea and the Nile River. Traditional navigation locks depended on a plentiful supply of water. At the present day, traditional navigation locks transit vessels between higher and lower elevations along the Mississippi River system and also the St Lawrence Seaway. The operators of the European Barge Canal system developed methods by which to reduce the volume of water required to transit pairs of ships sailing in opposite directions.
New Generation Hydraulics
The introduction of a side tank or side reservoir at each navigation lock has been proven to reduce water usage by 60 to 67 percent. When plans were initiated to enlarge the Panama Canal to transit much larger ships, designers included the European side tank system to reduce water consumption at navigation locks.
While saving water at navigation locks is a desirable objective, various constraints either prevent the installation of side tanks or the cost of installing side tanks becomes prohibitive. Recent advances in water turbine technology and water pump technology offer to reduce navigation lock water consumption.
The power generation industry historically preferred mega-scale hydraulic turbines, the result of economy of scale. While small and low-power turbines were popular toward the end of the 19th century, the technology practically became extinct until modern initiatives sought to develop small-scale hydroelectric power generation along small rivers and streams. The result has been the appearance of a new generation of small-scale turbines that operate at high efficiency, complimented by the development of small scale pumps that also operate at higher efficiency.
There may be scope to adapt new generation small-scale hydraulic technology to navigation locks.
Filling the Lock
When a vessel sails upstream, there is the need to fill the navigation lock with water from upstream. That water could flow from upstream and through small turbines and into the lock.
The turbines would drive pumps that could transfer up to on third water volume from downstream into the lock. There may be a need to use more than one design of turbine and more than one design of pump to maximize the volume of water being transferred from the downstream reservoir.
Emptying the Lock
When a vessel sails downstream, there is the need to empty the lock and flow the water downstream. That water could also flow through turbines that drive pumps that could transfer up to one thi3rd of the water from the lock to the upstream reservoir. Again, more than one design of turbine and more than one design of pump could maximize the volume of water being transferred from the lock to the upstream reservoir.
Some innovation in the piping system as well as in the installation of the turbine and pump assembly could allow a single set of turbines to perform double duty, that is, extract power from water flowing into the lock from upstream as well as from the lock to the downstream reservoir. Innovative design would need to allow turbines and pumps to move between a high elevation and a low elevation in relation to the navigation lock. A greater design challenge would seek to use minimal turbines and pumps to save water at a multi-level series of navigation locks.
Venturi Water Pump
Venturi water pumps are free from moving parts and use a fast flow of water to pump water from lower elevation. It may be possible to install venturi water pumps with multi-jet nozzles between an upstream reservoir and a lock, to pump 10 to 25 percent of water volume from downstream into the lock. Water from upstream would initially flow through a single jet, with other jets sequentially entering service as water level in the lock rises. A one-way flap or valve would prevent water running back downstream as water level inside the lock is being raised.
The first stage of pumping would involve venture pumps while the second stage of pumping would involve turbines and mechanical pumps.
Ram pumps are a proven technology that can be installed in a downward flowing stream to pump a small percentage of water to higher elevation, including as high as 25 times the change of height of the stream. When a lock is being emptied and water flows downstream to lower elevation, water may flow via ram pumps to pump 10 percent to perhaps as high as 20 percent of the water into the upstream reservoir. Further research into the performance of ram pumps could increase the percentage of water that could be pumped into the upstream reservoir.
Further research could determine as to whether ram pumps at navigation locks could achieve the performance levels of turbine/mechanical-pump combinations.
Drought and Waterways
America’s Mississippi Inland Waterway system has at times had to reduce barge traffic or even close to navigation as a result of drought conditions along certain sections of the waterway. There have been times when summer drought conditions resulted ships sailing along some sections of the St Lawrence Seaway at reduced payload due to a reduction in navigation depth. The Beauharnois navigation locks located to the southwest of Montreal as well as some other navigation locks has no provision for the installation of side tanks, leaving turbine-and-pump as a possible water saving option.
Pump-and-turbine water saving technology could be installed at navigation locks along recreational waterways. The volume of boat traffic may not otherwise warrant the cost of construction of side tanks along older canals. The comparatively small volumes of water involved in transit of vessels at navigation locks along recreational waterways could even warrant installation of electrically powered pumps to transfer water upstream during transit operations.
The idea of combining turbine-and-pump technology with side tanks at navigation locks is an area of possible future research. Assume that a downstream bound vessel enters a navigation lock with an adjacent empty side tank. During the descent, water would flow from the lock and through a turbine into the side tank while a pump transfers a portion of the water to the upper reservoir. At equilibrium, water level in both lock and side tank would be identical, except that the due to the volume of the vessel hull, the side tank would hold greater water volume.
Water would then flow downstream from navigation lock and through a turbine, with pump transferring some water into the side tank. During upstream operation, water would flow from side tank through turbine into navigation lock and pump some water from downstream into the lock. When equilibrium occurs between lock and side tank, water from upstream may flow through turbine into the lock and pump additional water from side tank into the lock. The combination of side tanks, turbines and pumps could reduce lock water usage by over 70 percent and be a future option for the Panama Canal.
Venturi Pumps and Side Tanks
The may be scope to combine venture pumps with side tanks at navigation locks for the purpose of reducing water usage to transit ships. During filling of the lock, water may flow from side tank through a venture pump to move some water from downstream via a one-way flap into the lock. At a later stage, water would flow from upstream through a venture pump to pull some additional water from the side tank via a one-way flap into the lock. The final stage of filling the lock would involve the use of turbines and mechanical pumps.
Ram Pumps and Side Tanks
When the lock is being emptied and water flowed downstream, ram pumps could pump a percentage of water to higher elevation into either the side tank or into the upstream reservoir. Further research would determine as to whether ram pumps could approach the performance levels of turbine/mechanical-pump combinations to assist in reducing water consumption at navigation locks.
The possible installation of turbines-and-pumps at navigation locks to reduce water usage during vessel transit operations as well as combining turbine-and-pump technology with side tanks warrants further evaluation. There is also the option of installing venture pumps at navigation locks, along with one-way valves to assist in reducing water usage to transit ships. Navigation locks along recreational waterways and inland waterways such as the Mississippi system and St Lawrence Seaway would be potential sites for either of both on venture pump technology and/or turbine-and- mechanical-pump technology.
Testing of the combination of either or both of venture pumps and/or turbine-and-mechanical-pumps with side tanks could be undertaken at locks along the European barge canal system. The test results and related research could be the basis for possible venture pump and/or turbine-and-mechanical-pump technology installation at locks/side-tanks along the Panama Canal.
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.