The Kanawha Canal on the James River in Virginia
By Ben R. Londeree
The Kanawha Canal idea was conceived by George Washington and he presented it to the Virginia legislature in 1784 as a way to connect Virginia’s western counties with the Atlantic seaboard by connecting the James River in eastern Virginia to the Kanawha River in western Virginia. The former drains east to the Atlantic Ocean and the latter drains west to the Ohio River, then into the Mississippi River, and finally into the Gulf of Mexico. The western counties were comprised of what now are Ohio, West Virginia, and Kentucky. Several writers (including Dunaway, Gibson, and Hobbs) have claimed that the Kanawha Canal was the biggest public works project in Virginia ever.
Since water seeks the lowest level, canals must be flat and changes in elevation are made with locks. Canals with locks were required to bypass rapids and falls on the James River and to change elevation on the Kanawha Canal. The project would have to cross the Blue Ridge and the Allegheny Mountains. The initial plan was to use rivers where practical and use canals for the unnavigable sections. The rivers would need to be cleared of debris and rocks to open up navigable channels. The terrain ranged from near swamps, through granite cliffs, unstable soils, and hills.
The number one obstacle was finances throughout the period from 1785 to 1880. A lot of money was needed to pay for surveying, design work, land, materials used in construction, labor, and maintenance. The legislature authorized the formation of the James River and Kanawha Canal Company and for it to sell stock to raise money. The costs were woefully underestimated most of the time. Subscription for stock could be made with a small down payment with promises to pay the balance in future installments. The legislature subscribed to a substantial portion of the stock. All of the stock sold quickly. However the economy recessed, so many of those whom had subscribed to stock including the legislature were unable to make their payments. Others probably decided to default to cut their losses. The legislature authorized the selling of more stock in 1790, but the second time around it was a hard sell. Again in 1832 with the formation of the James River and Kanawha Company, it required three years before all of the stock was sold and work could commence. (Gibson, p. 45)
A second and continuing problem throughout the period of 1785-1880 was political fighting among various factions and individuals. There were supporters and opponents of the canal. There were railroad supporters. There were regional factions. There were people with very strong personalities who were very determined to get there way.
The first attempt to build the canal system was in the Richmond area. Those in charge had little or no experience with canal and lock building. The work was to start in the lowlands which were swampy. Free men refused to work in those conditions. Slaves were rented from plantations in the area and bought in the open market. Then there was the added cost of housing and feeding them. Whites refused to work with blacks. So what resulted were black work gangs with white overseers. Much of the work was very low skill dominated by brawn, shovels, wheelbarrows, and carts pulled by mules, oxen, or horses. The building of locks, culverts, aqueducts, and walls; mining and creating well-shaped blocks of rocks; and the use of TNT to break up granite cliffs required skilled artisans who generally were white but had black helpers. Gibson (p. 41) stated that in this first round the workforce included about 10 whites and 100 slaves.
The initial project actually was two canals: an upper short canal and a lower long flat canal with a three mile stretch of the James River in between for a total distance of seven miles. These distances probably weren’t correct because the canal built in 1840 stated that Westham was 5.5 miles from Richmond. (James River) The upper canal was 200 yards long and included two granite locks with a total lift of 12-14 feet, (Gibson, p. 42) although (Dunaway, p. 33) cited Gallatin’s report which stated that there were 3 locks and a total lift of 34 feet. Gibson opined that Gallatin probably didn’t physically visit the locks. The upper canal was supplied water from a pool created by a dam above the falls near then Westham, Va. It probably was on the same line of a canal built by the previous landowner. (Gibson, pp. 29-30) The lower canal was 3.5 miles long and extended to Shockoe Hill in Richmond. (Dunaway, p. 33) The lower canal was supplied water via a sluice off of the James River. Since the canal was level and the river sloped downward, the canal had to be built up more and more on its route to Richmond. The selection of the origin of the lower canal probably was upstream at an elevation higher than the Great (turning) Basin to provide the basin with a steady source of water. The elevated canal provided room for culverts and aqueducts so that creeks could flow unimpeded into the James River. (Gibson, pp. 29-30) The lower canal ended at the Great Basin where boats could unload, reload, and turn around for the return trip upstream. (The basin was located between the current 8th, 11th, Cary, and Canal Streets.) The basin became surrounded by warehouses. (James Center History)
Although everything was not complete, the canals were usable starting in 1789. (Hobbs, p. 3) These canals were the first to use locks in the United States. (Hobbs, p. 3) Partial tolls were collected starting in 1794. (Gibson, p. 45) The Great Basin was completed in 1800. (Gibson, p. 45; Hobbs p. 3) Navigation channels were opened up in the James River to Crow’s Ferry (220 miles upriver from Richmond (Gibson, p. 45)), the North River to Lexington, and the Rivanna River to Charlottesville. (Hobbs, p. 3) The channels were created by removing debris and rocks and by building underwater weirs that directed flow into the channels. These navigation channels in the rivers allowed long flat-bottomed boats (batteaux) to travel these streams. However, the journeys remained dangerous. And finally a wagon trail was developed through the Blue Ridge and Allegheny Mountains.
By 1800 the canal and Great Basin were completed and opened from Richmond to Westham. Starting in 1796, full tolls were charged. (Gibson, p. 45) The income for the most part was not invested in maintaining or extending the canal. Instead of reinvesting profits, dividends were distributed to investors, including the legislature.
The upriver shippers still complained that the James River and side streams were hardly navigable and were very dangerous for cargo and life. Likewise there were many complaints about the poor quality and maintenance of the canal, sluices, locks, and the dam.
The shippers also complained about the lack of locks to the Richmond Dock located in the tidewaters. Without the locks, freight had to be transferred from boats to wagons at the Great Basin. Then the freight was stored temporarily in warehouses near to the basin or the wagons were pulled by horses or mules down to the Richmond Dock where the wagons were unloaded and the freight was stored in warehouses at the dock. This sequence of events increased the cost of shipping. Finally after years of complaining and orders from the legislature, a canal and 13 locks were built down to the tidewater in about 1816.
Between 1816 and 1819, the Richmond Dock Company extended Chapel Island southeast to the “north” shore of the James River. (The River coursed southeast at this location.) A big ship lock was built which served as a dam to create an elevated stable pond next to the docks. The big ship lock also served as a way to raise ocean going ships up to the pond. (Port of Virginia website) In 1841, the James River and Kanawha Company bought the Richmond Dock Company. (Gibson, p. 223) We will return to this topic later.
With the backdrop of so many complaints, the Commonwealth of Virginia bought the charter from the James River and Kanawha Canal Company in 1820. It agreed to pay the investors rather generous returns for many years in the future. Little was done at first. Starting in 1823, financing was provided by the legislature and major repairs, rebuilds, and improvements were made on the canal and river beds. The canal was extended 30 miles upstream to Maiden’s Adventure Dam by 1826. (Gibson, p. 89) This section included 10 lift locks, 5 guard locks, 5 aqueducts, 9 culverts, 4 dams, and 38 bridges over the canal. (Gibson, p.89) A seven mile section of canal was built through the Blue Ridge Gorge parallel to the wagon trail. (Gibson, p. 89) However, there were problems with the quality of all of this work. And then, financial limitations stopped everything again.
In 1832, the Virginia Legislature approved a charter for a new James River and Kanawha Company with the requirement that $5,000,000 would need to be raised before receiving final approval. Of the total, $4,000,000 had to be raised in subscriptions to company stock and a $1,000,000 loan was authorized. (Gibson, p. 114) Joseph Carrington Cabell (a legislator) was one of the leading forces up to this time and especially in moving forward. He spent three years fundraising, “arm-twisting”, pleading, and overpromising about the outcome. The legislature did increase their subscription. Finally in 1835, the conditions were met and the legislature gave the okay to commence. (Gibson, p. 131)
Cabell became the president of the James River and Kanawha Company. The company was contracted to construct canals and/or railroads from the tidewater of the James River to the navigable waters of the Ohio River. He was given considerable latitude in deciding on the transportation infrastructure and how it would be done. Most of the previous canal work was of little use and work had to start almost from scratch. First he decided to build a canal from Richmond to Lynchburg. He hired a reputable engineer, Benjamin Wright from New York, who had successful experience in canal building. Wright hired three assistant engineers with canal building experience. Each assistant oversaw one of three segments of the canal: 1) Maiden’s Adventure Dam to Scottsville, 2) Scottsville to Tye River, and 3) Tye River to Lynchburg. Each assistant subdivided the canal segments into sub-segments and hired engineers to oversee them. (Gibson, pp. 135-6; Hobbs, p. 11) Surveying commenced from Richmond to Lynchburg. Needed land was purchased or condemned. Design work was completed. Contracts were awarded for 201 sub-segments. However, many contractors abandoned their contracts for various reasons so new contractors had to be found. (Gibson, p. 154) The region downstream from Maiden’s Adventure Dam was started in 1837 after the three upstream segments were underway. (Hobbs, p. 18)
As with earlier canal work, hiring laborers was difficult. Rented and bought slaves did most of the unskilled work. Irish immigrants also were hired. There was a shortage of artisans due to the work on northern canals so some had to be recruited from Europe. (Hobbs, p. 27) Dunaway (p. 130) stated that 3,300 people were employed for this project as of 1837.
The canal was to be at least 50 feet wide at water level and 30 feet wide at the bottom of the canal. Leading into Richmond the canal was wider and deeper to supply water for power. (Gibson, p. 167) The canal sides were to be at a 50% grade and extend two feet above the water. The water was to be five feet deep. The towpath was to be 12 feet wide and the berm on the opposite side was to be eight feet wide. Both towpath and berm were to slope slightly away from the canal. The canal was lined with a special type of clay to prevent water loss. Since poles would puncture the waterproof seal, they could not be used for propulsion; thus horses and mules were required for towing boats. The locks were to be 15 feet wide and 93 feet long. (More details about locks can be found at the end of this paper.) Details were specified for dams, weirs, culverts, aqueducts, and other infrastructure as well. The culverts and aqueducts were used to allow water from storm ditches, creeks, and rivers to flow easily under the canal into the James River. (Hobbs, p. 12) Rip-rap often was used to armor the river side of the walls. In some cases river walls were constructed. Never-the-less, numerous problems arose in the next five years including financial, condemnation proceedings, engineering problems, contractor problems, labor issues, weather issues, and floods. For example, some lock walls bowed in so that they were less than 15 feet apart; some had to be rebuilt. Often specs had to be modified for site specific issues.
In order to insure adequate water, the James River and Kanawha Company contracted with the Lynchburg waterworks to assume control of their dam. (Hobbs, p. 18) A major flood destroyed the dam in 1836. (Hobbs, p. 18) The dam had to be rebuilt and the new one was built with cut stone and included a segment dedicated to the canal and a segment for a fish ladder.
Even with these problems, Cabell’s driving force and the hiring of qualified and experienced engineers and contractors led to a surprisingly well-built canal from Richmond to Lynchburg by December 1840. (Hobbs, p. 30) It was nearly continuous and 146.5 miles long. (Hobbs, p. 30) Near Lynchburg there was a rope ferry crossing from the north to south side of the James River. (Hobbs, p. 30) The locks accommodated ships with 14.5 foot beams (width), up to 93 feet long, and up to 80 tons of weight when loaded.
Using T. Gibson Hobbs, Jr.’s maps (pp. 116-161) of the Kanawha Canal between Richmond and Lynchburg, the various canal components were identified and enumerated. There were 51 numbered locks, I unnumbered lock, 2 river locks (locks to the James River), 2 guard locks (let water into the canal), 8 dams, 2 sluice gates (let boats and/or water in), 12 aqueducts, 29 culverts, 2 bridges over the canal, 4 basins for turning and/or storage of water, numerous abutments, and several massive walls. Hobbs (p. 26) stated that in the Richmond to Lynchburg segment there were 191 culverts, 11 aqueducts, 133 farm bridges, locks, and gatekeeper houses. Dunaway (p. 146) stated that there were 58 locks, 11 aqueducts, 191 culverts, and 133 road and farm bridges. The 1840 toll tables listed 51 locks which were located from 0.1 mile to 5.3 miles apart for a total distance of 146.3 miles. The distances from Richmond were: Lock #1 3.3 miles, Westham 5.5 miles (Lock #3), Maiden’s adventure dam 27.9 miles, Cartersville Road 46.6 miles (Lock #12), Scottsville Basin 79.3 miles, Rockfish Aqueduct 90.6 miles (Lock #28), Hardwicksville 103.2 miles (Lock #32), Staples’ mills 130.4 miles, crossing of James River 136.1 miles, and Lynchburg Basin 146.3 miles. (James River) The change in elevation from Richmond to Lynchburg is approximately 475 feet divided by the number of lift locks (51) resulting in an average lift per lock of over 9 feet assuming that they all lifted going upstream. Actually there was one lock that lowered the boats near Lynchburg. From Hobbs’ pictures, the aqueducts appeared to be larger than the biggest culverts, but it was not always the case. I believe that Hobbs called it an aqueduct if there were vertical sections to the walls. Both styles had one or more stone arches. The various structures in the pictures were approaching 180 years old. Some of the aqueducts and culverts looked like they were still functional.
This time some of the profits were used for maintenance and upgrades. Railings were added to the aqueducts. Lamps were added at each of the locks. Other improvements included road bridges, foot bridges, outlet locks, head gates (to lower canal water level), feeders (to increase the canal water level), dams, and 47 lock houses. (Dunaway, p. 133) The canal was extended to Buchanan, VA in the Blue Ridge Mountains by 1851. (Hobbs, p. 39 and Dunaway, p. 157) The previous canal in this region had to be totally rebuilt. This new canal was a separate system from the Richmond to Lynchburg system. This canal was discontinuous and the river was used for 9 miles. (Dunaway, p. 157) The canal started on the south side of the James River above the Lynchburg Waterworks Dam and there was one ferry crossover to the north side. An analysis using Hobbs’ maps (pp. 102-116) showed that this section had 25 lift locks, 6 guard locks, 14 dams, 5 weirs, 2 aqueducts, 15 culverts, numerous abutments, and a number of river walls. Dunaway (p. 157) stated that there were 38 locks, 4 stone dams, 7 timber dams, 48 square drains, 17 tow path bridges, 8 culverts, 2 farm bridges, and 1 street bridge over the 50 miles for a total distance from Richmond to Buchanan of 196.5 miles. Work was started on the canal segment between Buchanan and Covington but was stopped in 1856 due the lack of money. (Hobbs, p. 44) Some of the locks, culverts, aqueducts, dams, and tow paths were finished. Some were not finished and some were not started. The 192 foot Mason tunnel was finished but the 1,900 foot Marshall Tunnel was started but not finished. (Hobbs, p. 44 and pp. 97-102) Roads (turnpikes) were improved and the Kanawha River navigation channels were improved into Kanawha County. (Dunaway, p. 148)
Cabell resigned in 1845 and was replaced by Walter Gwynn in 1846. (Hobbs, pp. 34-5 and Dunaway, p. 240) Cabell remained in the picture with various reports. In 1847 W. B. Chittenden was elected president. (Hobbs, p. 36 and Dunaway, p. 240) He died in 1849 and John Y. Mason served as president from 1849 to 1853. (Hobbs, p. 37 and Dunaway, p. 240) Subsequent presidents were Thomas H. Ellis, (Hobbs, p. 47 and Dunaway, p. 240) Edward Lorraine, (Hobbs, p. 47 and Dunaway, p. 240) Charles S. Carrington, (Gibson, p. 293 and Dunaway, p. 240) and John W. Johnston. (Gibson, p. 300 and Dunaway, p. 240)
In 1849 the Tidewater Connection from the Great Basin to the Richmond Dock was authorized by the legislature and finished in 1854. It was connected to the Great Basin via a canal and featured 5 granite locks (15 feet by 100 feet each) with a total drop of 69 feet in the span of 3.5 city blocks. (Tidewater) There were basins between locks #1 and #2 and locks #3 and #4. (Antebellum) (Remnants of locks #4 and #5 without gates still exist in a park between 12th and 13th streets and 195 expressway and Byrd Street. The park entrance is on 12th Street) There was a big ship lock/dam at the opposite end of the pond/canal. The granite dock area (upper dock plus lower dock) was nearly one mile long. The granite dock no longer exists; however, it was protected from the tidewater by the 100-200 feet wide and 11 – 15 feet deep pond/canal between the mainland and Chapel Island. (Dunaway, p. 164) A mill race (now called Haxall Canal) for water supply extended from the upper dock to the James River over 800 yards upstream between Brown Island and the mainland. (U. S. Coast Survey Office and Google Earth map) The mill race pre-existed the first tidewater locks to provide water to power nearby mills but was a ready source of water for the dock area. An 1858 map showed the mill race connected to the Tidewater Locks and upper dock and what appeared to be a second opening between the upper dock and the James River. (U. S. Coast Guard Survey Office) Now the connection between Haxall Canal and the Tidewater Connection is via a pipe at the lower end of lock #5. A short distance upstream of the big ship lock there was and still is a dam that lets out excessive water so as to maintain a constant water level in the dock area. The big ship lock allowed the big ships to rise up to 15.5 feet on the depth gauge from the tidewater to the dock area pond/canal where the water was calm. (Dunaway, p. 164) The actual lift depended on the tide water level which varied by 2 - 4+ feet each day. The big ship lock was made of granite with inside dimensions of 35 feet wide and 185 feet long (Dunaway, p. 164) or 30 feet by 180 feet. (Gibson, p. 257) The upper and lower gates each had 4 small lift gates (paddles) operated from above (a worm gear or a bevel gear system to convert from rotation of a vertical shaft to rotation of a horizontal shaft). The gates themselves were opened and closed manually with rack and pinion gearing operated from above on each side of the lock. All of these improvements replaced wooden locks and canals built in the mid to late 1810s that were too small and in bad shape.
Two other projects were approved in 1849: a bridge to replace the ferry near Lynchburg and a lock and short canal for access to the Rivanna River from the Kanawha Canal. I could find no evidence about the existence of the bridge. The Rivanna Connection (lock and canal) was built in 1851 (Gibson, p. 254) and eventually connected to the Rivanna Canal.
During 1854-1855 bridges to the south side of the James River were completed at New Canton, Hardwicksville, and Bent Creek. Also, a dam, river lock, and lateral canal were built at Cartersville. (Dunaway, p. 161)
Two other canal companies formed for the north-side rivers: Rivanna Navigation Company and North River Navigation Company. The former must have been absorbed by the James River and Kanawha Company because it later was listed as such. The North River Navigation Company was purchased in 1858 by the James River and Kanawha Company. (Hobbs, p. 45 and Dunaway, p, 161-162)
Many new boats called packets were built that maximized capacities to move goods and people on the new canal. Typically the packets had a long cabin to accommodate freight or people. Different packets were designed for freight or people. Three companies were chartered to provide boats and services for freight and passengers. One of these companies; Boyd, Edmonds, and Davenport; ended up dominating packet travel. (Gibson, p. 205) There may have been some independent contractors using the canal as well. Each boat typically was pulled by two pairs of horses or mules. One pair pulled while the other pair rested on board the packet. A boy (hoggie) tended to the animals. A captain ran the packet and he had a small crew, typically two. On the larger packets food was served; a place for sleeping was provided; and bathroom facilities were provided. For a passenger boat the trip from Lynchburg to Richmond (downstream) took about 33 hours and the return trip took about 35 hours travelling day and night. (Gibson, p.199) Freight boats took 3.5 days upstream and 3 days downstream. (Dunaway, p. 170) Passing other packets required some cooperation to avoid getting the tow ropes tangled. One boat stopped to let its ropes sag so the other boat and animals could pass. Compared to other forms of shipping or traveling available at the time, the packets plying on the canal were much safer, smoother, and more efficient. Still, there were hardships including breakdowns, weather, and mosquitos. Smaller boats could use the locks but the high fees made it unlikely; they still could use the river channels.
The James River and Kanawha Company attempted to build a railroad from Buchanan to Clifton Forge to connect to the Covington and Ohio Railroad (C&O RR) in 1877. Convicts supplied much of the labor. (Dunaway, p. 230) Tunnels were dug through mountains to accommodate the railroad. However, a major flood destroyed much of their work in November of 1877. (Gibson, p. 301 and Dunaway, p. 230)
A side benefit of the canal was that there was enough water available to power machines in buildings near to the canal. Selling the water for this purpose was another source of revenue for the James River and Kanawha Company. This new power was a boon to Richmond. And in Lynchburg, the canal was widened in 1855 to accommodate increased need for water power. (Hobbs, p. 43)
Competition with the railroads made profits hard to come by and floods often damaged the infrastructure. So in 1880, the James River and Kanawha Company, on the edge of bankruptcy, was sold to the Richmond and Allegheny Railroad (formed in 1878 by approval of the legislature (Dunaway, p. 231). (Dunaway p. 239) The Richmond and Allegheny Railroad was required to maintain several parts of the canal for water power. (Dunaway, p. 238) Google aerial maps show that some parts of the canal still exist today. Much of the Kanawha towing path was converted to a railroad bed. After several mergers, the railroad continues to be used today by the CSX Transportation Railroad (CSX) to move coal from the mountains to the east coast of Virginia. (Gibson, p.304)
Antebellum Richmond, Virginia: Tidewater Connection (http://katlawren.blogspot.com/2014/04/tidewater-connection.html )
CSX Transportation System Map: https://www.csx.com/index.cfm/customers/maps/csx-system-map/
Dunaway, Wayland Fuller. History of the James River and Kanawha Company. New York: Wayland Fuller Dunaway, 1922 (https://archive.org/details/historyofjamesri00dunarich )
Gibson, Langhorne, Jr. Cabell’s Canal: The Story of the James River Kanawha. Richmond, Virginia: The Commodore Press, 2000.
Hobbs, T. Gibson, Jr. The Canal on the James: An Illustrated Guide to the James River and Kanawha Canal. Lynchburg, Virginia: Blackwell Press, 2009.
History of the James Center: http://thejamescenter.com/history.html
James River and Kanawha Company, The. Regulations for the James River and Kanawha Canal and Laws for Its Protection. Richmond: Shepard and Colin, 1840
Port of Virginia website http://www.virginiaplaces.org/transportation/shipportrichmond.html
Tidewater Connection Locks (http://www.hmdb.org/marker.asp?marker=23869 )
U. S. Coast Survey Office. Map of the City of Richmond, VA. U. S. Coast Survey Office, 1864 (http://www.civilwarrichmond.com/2-uncategorised/49-map-of-richmond-from-the-official-records-atlas-plate-lxxxix-2-prepared-in-1864-by-a-d-bache-for-the-u-s-coast-survey )
Essentials of locks in the 1800s
To raise or lower a boat to get past an obstacle, e.g. rapids, water fall, dam, or hill.
There is an upper pool of water created by a dam, weir, sluice, or canal.
There are curved walls that guide boats in to the lock. These walls are recessed to accommodate the open gates.
There is a somewhat water tight chamber (the lock) generally with an open top and large enough to accommodate the largest boats expected. (It may have a protective arch above the upper and lower gates.)
There is an upper gate for boat entry or exit that usually consists of two vertical doors on vertical hinges that when closed point upstream slightly and usually are operated manually from above using long timber levers with the hinge pin extended or a nearby post acting as a fulcrum.
A sill rises from the floor of the lock to just above the bottom of the upper gates to support and seal the gates. The height of the upper sill is equal to the lift plus the height of the lower sill and enough to create a good seal with the gates. When boats pass through the gates, there must be enough water so that the keel doesn’t hit the sill.
There is one or more small lift gates (paddles) to let water in to the lock from the upper pool without creating turbulence (baffled) and the lift mechanism (e. g. chain rolled up on a horizontal rod) usually is operated with an L-shaped windlass from above.
There is a lower gate for boat entry or exit that usually consists of two vertical doors on vertical hinges that when closed point upstream slightly and usually are operated manually from above using long timber levers with the hinge pin extended or a nearby post acting as a fulcrum.
A sill rises from the floor of the lock to just above the bottom of the lower gates to support and seal the gates. The height is enough to create a good seal with the gates. When the lock is ready for the boat to exit, there must be enough water so that keel doesn’t hit the sill.
There is one or more small lift gates (paddles) to let water out of the lock into the lower pool without creating turbulence (baffled) and the lift mechanism usually is operated with an L-shaped windlass from above.
Usually there are curved or angled walls leading into the upper and lower gates that guide boats in to the lock. The walls leading to the upper gate have a recessed area to accommodate the open gates. The recessed area for the lower gates is inside the lock.
Moor the boat and a crewman exits on each side of the boat with a windlass to operate the paddle gates.
With gates closed, use the windlasses to open the upper paddle gates gradually to fill the lock with water to the level of the upper pool.
Open the upper gates to let the boat in.
Close the upper gates and paddles.
Use the windlasses to open the lower paddle gates gradually to drain the lock to the level of the lower pool.
Open the lower gates to let the boat out and close the lower paddle gates.
The crewmen return to the boat with the windlasses.
Reverse the order of the above. By alternating between boats going upstream and downstream, a filling or emptying step can be skipped because the lock will be empty or filled from the previous process, e. g. when a boat exits going upstream the lock is ready for a downstream boat