Special cases Lock (water navigation)

1 special cases

1.1 lock flights
1.2 staircase locks
1.3 doubled, paired or twinned locks
1.4 stop locks
1.5 round locks
1.6 drop locks
1.7 flood locks
1.8 flood gates
1.9 bi-directional gates , locks
1.10 tidal locks
1.11 inlet locks
1.12 large locks

1.12.1 hiram m. chittenden locks

special cases
lock flights

the flight of 16 locks @ caen hill on kennet , avon canal

loosely, flight of locks series of locks in close-enough proximity identified single group. many reasons, flight of locks preferable same number of locks spread more widely: crews put ashore , picked once, rather multiple times; transition involves concentrated burst of effort, rather continually interrupted journey; lock keeper may stationed crews through flight quickly; , water in short supply, single pump can recycle water top of whole flight. need flight may determined purely lie of land, possible group locks purposely flights using cuttings or embankments postpone height change. examples: caen hill locks, devizes.

flight not synonymous staircase (see below). set of locks staircase if successive lock chambers share gate (i.e. not have separate top , bottom gates pound between them). flights not staircases, because each chamber separate lock (with own upper , lower gates), there navigable pound (however short) between each pair of locks, , locks operated in conventional way.

however, flights include (or consist entirely of) staircases. on grand union (leicester) canal, watford flight consists of four-chamber staircase , 3 separate locks; , foxton flight consists entirely of 2 adjacent 5-chamber staircases.

staircase locks

staircase of 5 locks, dating 1774, @ bingley, england

where steep gradient has climbed, lock staircase used. there 2 types of staircase, real , apparent .

a real staircase can thought of compressed flight, intermediate pounds have disappeared, , upper gate of 1 lock lower gate of 1 above it. however, incorrect use terms staircase , flight interchangeably: because of absence of intermediate pounds, operating staircase different operating flight. can more useful think of staircase single lock intermediate levels (the top gate normal top gate, , intermediate gates tall bottom gate). there no intermediate pound, chamber can filled emptying 1 above, or emptied filling 1 below: whole staircase has full of water (except bottom chamber) before boat starts ascend, or empty (except top chamber) before boat starts descend. building pair of such lock sets (one used climb , other descend) these difficulties avoided, enabling greater traffic volume , reduced wait times.

in apparent staircase chambers still have common gates, water not pass directly 1 chamber next, going instead via side ponds. means not necessary ensure flight full or empty before starting.

examples of famous real staircases in england bingley , grindley brook. two-rise staircases more common: snakeholme lock , struncheon hill lock on driffield navigation converted staircase locks after low water levels hindered navigation on bottom cill @ higher tides – new bottom chamber rises far enough boat on original lock cill. in china, completed 3 gorges dam includes double five-step staircase large ships, , ship lift vessels of less 3000 metric tons. examples of apparent staircases foxton locks , watford locks on leicester branch of grand union.

instructions descent of treble staircase, chesterfield canal

operation of staircase more involved flight. inexperienced boaters may find operating staircase locks difficult. key worries (apart being paralysed indecision) either sending down more water lower chambers can cope (flooding towpath, or sending wave along canal) or emptying intermediate chamber (although shows staircase lock can used emergency dry dock). avoid these mishaps, usual have whole staircase empty before starting descend, or full before starting ascend, apart initial chamber.

one striking difference in using staircase of either type (compared single lock, or flight) best sequence letting boats through. in single lock (or flight room boats pass) boats should ideally alternate in direction. in staircase, however, quicker boat follow previous 1 going in same direction. partly reason staircase locks such grindley brook, foxton, watford , bratch supervised lockkeepers, @ least during main cruising season, try alternate many boats up, followed down there chambers in flight.

as flight, possible on broad canal more 1 boat in staircase @ same time, managing without waste of water requires expertise. on english canals, staircase of more 2 chambers staffed: lockkeepers @ bingley (looking after both 5-rise , 3-rise ) ensure there no untoward events , boats moved through speedily , efficiently possible. such expertise permits miracles of boat balletics: boats travelling in opposite directions can pass each other halfway staircase moving sideways around each other; or @ peak times, 1 can have chambers full simultaneously boats travelling in same direction.

doubled, paired or twinned locks

doubled locks. left lock has boat in it, right lock (center of drawing) empty. on erie canal @ lockport

locks can built side side on same waterway. variously called doubling, pairing, or twinning. panama canal has 3 sets of double locks. doubling gives advantages in speed, avoiding hold-ups @ busy times , increasing chance of boat finding lock set in favour. there can water savings: locks may of different sizes, small boat not need empty large lock; or each lock may able act side pond (water-saving basin) other. in latter case, word used twinned : here indicating possibility of saving water synchronising operation of chambers water emptying chamber helps fill other. facility has long been withdrawn on english canals, although disused paddle gear can seen, @ hillmorton on oxford canal. elsewhere still in use; pair of twinned locks has been opened in 2014 on dortmund-ems canal near münster, germany.

the once-famous staircase @ lockport, new york doubled set of locks. 5 twinned locks allowed east- , west-bound boats climb or descend 60 feet (18 m) niagara escarpment, considerable engineering feat in nineteenth century. while lockport today has 2 large steel locks, half of old twin stair acts spillway , can still seen (without lock gates).

these terms can (in different places or different people) mean either two-chamber staircase (e.g. turner wood double locks on chesterfield canal: same canal has three-rise staircase called thorpe low treble locks), or flight of 2 locks (as @ thornhill double locks on calder , hebble navigation). also, double lock (less often, twin lock ) used novices on english canals mean wide (14 ft) lock, presumably because double width of narrow lock, , allows 2 narrow boats going in same direction double . these known broad locks.

stop locks

lifford lane guillotine lock, kings norton, birmingham between stratford-upon-avon canal , worcester , birmingham canal

a stop lock (very) low-rise lock built @ junction of 2 (rival) canals prevent water passing between them.

during competitive years of english waterways system, established canal company refuse allow connection newer, adjacent one. situation created worcester bar in birmingham, goods had transshipped between boats on rival canals feet apart.

where junction built, either because older canal company saw advantage in connection, or new company managed insert mandatory connection act of parliament, old company seek protect (and enhance) water supply. normally, specify that, @ junction, newer canal must @ higher level existing canal. though drop newer older canal might few inches, difference in levels still required lock – called stop lock, because stop water flowing continuously between newer canal , older, lower one. lock under control of new company, , gates would, of course, point uphill - towards newer canal. protect water supply of newer canal, nevertheless donate lockful of water older company every time boat went through. in times of excess water, of course, lock bywash continuously supply water lower canal.

when variable conditions meant higher water level in new canal not guaranteed, older company build stop lock (under own control, gates pointing towards own canal) closed when new canal low. resulted in sequential pair of locks, gates pointing in opposite directions: 1 example @ hall green near kidsgrove, southern terminus of macclesfield canal joined hall green branch of earlier trent , mersey canal. 4 gate stop lock near kings norton junction, between stratford-upon-avon canal , worcester , birmingham canal replaced in 1914 pair of guillotine lock gates stopped water flow regardless of canal higher. these gates have been permanently open since nationalisation.

many stop locks removed or converted single gate after nationalisation in 1948. hall green stop lock remains, single lock: lock removed because lowering of t&m s summit pound (to improve harecastle tunnel s air draught – free height above water level) meant t&m lower macclesfield. hall green branch considered extension of macclesfield canal, meets t&m @ hardings wood junction (just short of harecastle tunnel north portal).

it should noted newer canal not @ higher level 1 joined. instance, there shallow lock @ autherley junction, 1835 birmingham , liverpool canal (now part of shropshire union canal) met older staffordshire , worcestershire canal, build in 1772. nicholson guide shows boater travelling south along newer canal locks before turning north or south onto older staffordshire , worcestershire canal – shropshire union canal gains small lockful of water each time boat passes. however, gain tiny since level difference small possible open both gates @ once.

round locks

agde round lock

there several examples locks have been built round plan, more 2 exits lock chamber, each serving different water level. lock serves both way of changing levels , junction. circular plan of lock allows boats within rotate line appropriate exit gate.

the best known example of such round lock agde round lock on canal du midi in france. serves lock on main line of canal , allows access hérault river.

a second french round lock can found in form of the, disused, Écluse des lorraines, connecting canal latéral à la loire river allier.

drop locks

dalmuir drop lock

a drop lock allows short length of canal lowered temporarily while boat passes under obstruction such low bridge. during canal restoration, drop lock may used impractical or prohibitively expensive remove or raise structure built after canal closed (and re-routing canal not possible).

a drop lock can consist of 2 conventional lock chambers leading sump pound, or single long chamber incorporating sump - although term applies second case. pounds @ either end of structure @ same height, lock can emptied either allowing water run waste sump lower stream or drain, or (less wastefully) pumping water canal. particularly in two-chamber type, there need bypass culvert, allow water move along interrupted pound , supply locks further down canal. in case of single-chamber type, can achieved keeping lock full , leaving gates open while not in use.

while concept has been suggested in number of cases, example in world of drop lock has been constructed @ dalmuir on forth , clyde canal in scotland. lock, of single chamber type, incorporated during restoration of canal, allow replacement of swing bridge (on busy road) fixed bridge, , answer criticisms restoration of canal cause frequent interruptions of heavy road traffic. can emptied pumping – uses lot of electricity method used when water supplies adequate drain lock nearby burn. series of pictures showing operation of lock can seen here.

flood locks

a flood lock prevent river flooding connected waterway. typically installed canal leaves river. @ normal river levels, lock gates left open, , height of canal allowed rise , fall height of river.

however, if river floods beyond safe limit canal, gates closed (and lock created) until river drops again. since true lock possible boats leave canal flooded river despite difference in water levels (though not wise) or (more sensibly) allow boats caught out on flood gain refuge in canal.

note if canal navigation cut connecting 2 stretches of same river, flood lock @ upstream end of cut (the downstream end have conventional lock).

flood locks have been used flood gates (see below) incapable of reverting former purpose without refurbishment. is, outer gates ever closed (probably because waterway not true commercial one, , therefore there no financial imperative boat venture out onto flooded river) inner gates suffer lack of maintenance. example on calder , hebble navigation, structures referred in boating guides flood locks capable of being used flood-prevention, not penning boats or river in flood.

flood gates


bi-directional flood gates on canal schoten-dessel, belgium



flood gate or stop gate (american usage) on chesapeake , ohio canal. when flood threatened, boards put in lock divert waters canal potomac river. note winch house on top boards.

a flood gate or stop gate cheaper equivalent of flood lock. 1 set of gates exist, , when river higher canal, gates closed , navigation ceases. these quite common in french inland waterways system. flood gates may used sub-divide long canal pounds or protect, in case of bank collapse, surrounding area if lower water level of canal. commonly found @ ends of long embankments , @ aqueducts. these gates overlooked because lack balance beams , little higher normal canal level.

bi-directional gates , locks

bi-directional gates @ 1 chamber end of tidal lock (located in veurne on canal nieuwpoort - duinkerke)

where lock tidal (i.e. 1 side of lock has water level varies tide) or canal meets river level may vary, water on tidal or river side (the downstream side) may rise above water on normal upper side. upstream pointing doors fail job, , drift open. prevent water flowing wrong way through lock, there need @ least 1 set of gates pointing in wrong direction. if desirable boats can use lock in these circumstances, there needs full set of gates pointing towards tidal or river side. usual method have gates pointing in opposite directions @ both ends of chamber (alternatively, paired stop lock arrangement of 2 separate sequential locks pointing in opposite directions work here – require chamber). if navigation not required (or impossible) @ 1 extreme (e.g. allow navigation above mid-tide, prevent canal emptying @ low tide) necessary have 1 set of bi-directional gates.

two types of bidirectional locks @ end of marne-rhine canal in independent port of strasbourg

a sea lock 1 connects canal or river directly estuary or ocean. sea locks tidal.

tidal locks

sea lock @ bude, cornwall

a tidal lock lock connects tidal non-tidal water. includes lock between tidal river , non-tidal reaches, or between tidal river , canal, or sea lock. however, term refers lock method of operation affected state of tide. examples:

a canal joining river levels lower canal. needed ordinary lock, gates pointing canal. lock used long tide high enough float boats through lower gates. if near low tide lock becomes unusable, gates can barred (and become reverse flood gate , holding water in canal). arrangement applies sea locks (e.g. bude canal).
a canal joining river below it, can rise above (at high tides, or after heavy rain). 1 pair of gates can made bidirectional, i.e. inward-pointing gates supplemented pair pointing out river. when river higher canal, normal gates drift open, additional pair of gates can closed protect canal, , prevent navigation river. in effect, have added flood gate.
as above, safe navigate when river higher canal. lock bidirectional (two pairs of oppositely pointing gates @ each end) allow boats pass @ normal river levels. @ extreme low or high tides unsuitable navigation, appropriate sets of gates barred prevent passage.

inlet locks

inlet lock (left) feeder canal, regulates water potomac river c&o canal. lift lock (right) allows boats continue canal in normal fashion.

an inlet lock regulate water feeder canal or river main canal. in cases, inlet lock may double lift lock allow boats river slackwater. note in example on right, feeder canal george washington s little falls skirting canal part of potomac company s canals, later re-purposed feeder canal chesapeake , ohio canal.

very large locks

berendrecht lock (right) , zandvliet lock (left), located @ entrance port of antwerp (top) scheldt (foreground)



barges @ lock on mississippi river

the world s largest lock was, until 2016, berendrecht lock, giving access port of antwerp in belgium. in 2016 kieldrechtsluis in same port became largest. lock 500 m (1,600 ft) long, , 68 m (223 ft) wide , drops 17.8 m (58 ft), , has 4 sliding lock gates. size of locks cannot compared without considering difference in water level designed operate under. example, bollène lock on river rhône has fall of @ least 23 m (75 ft), leerstetten, eckersmühlen , hilpoltstein locks on rhine–main–danube canal have fall of 24.67 m (80.9 ft), each , oskemen lock on irtysh river in kazakhstan has drop of 42 m (138 ft). total volume of water considered in lock equals product of length, breadth , difference in water levels. lock staircases used in attempt reduce total volume of water required in relation amount of useful work done. useful work done relates weight of vessel , height lifted. when vessel lowered consumption of potential energy of water consumed considered. alternative locks boat lift; facilities of type, e.g. anderton boat lift or strépy-thieu boat lift in belgium, not rely on consumption of water primary power source, powered motors , designed consume minimum amount of water.

the 29 locks on mississippi river typically 600 feet (180 m) long while tug , barge combinations as 1,200 feet (370 m) long consisting of many 15 barges , 1 tug. in these cases, of barges locked through, using partially opened lock valves create current pull un-powered barges out of lock tied wait rest of barges , tug pass through lock. can take as hour , half pass lock.

hiram m. chittenden locks

every november, large lock of hiram m. chittenden locks (better known locally ballard locks in reference seattle neighborhood located in) emptied maintenance, seen in november 2004 pictures below. provides opportunity visualize how lock works without water obscuring bottom of lock. reference, picture far left shows lock in operation, tug , barge (loaded sand , gravel) waiting gates open. in bottom left corner of picture may seen cut-out in side wall contains gate when open.

the lock has 3 pairs of gates, 1 pair @ each end , 1 pair in middle half length of lock can used when whole length not required, saving water. barely visible person walking along bottom of lock in second picture gives indication of vast size of lock. in both pictures of end gates, string of penstock openings visible along sides @ bottom. water entering , leaving lock flows gravity through these openings. requires around 15 minutes fill or empty lock.