Operation Profiles of Hydraulic Closures

C H A P T E R

2 Operation Profiles of Hydraulic Closures 2.1 GENERAL REQUIREMENTS Hydraulic gates are utilized in different kinds of facilities that serve different purposes. For example, a navigation lock is a site that—as the name says—facilitates navigation, while the main purpose of a flood barrier is to facilitate land defense against inundation. Yet, they both utilize movable hydraulic closures, or for short hydraulic gates. The very fact that they do this does not imply, however, that they do it in the same way. The gates in a navigation lock are usually operated a few dozen times a day, while those in a flood barrier may be operated once a year for testing and once in 5–10 years for the actual flood defense. This generates a number of other differences in gate operation. We will, therefore distinguish a number of different application groups for hydraulic gates—and call these groups “operation profiles.” The following sections introduce such profiles, describing the general operation purposes, main features, and the resulting specific requirements for hydraulic gates. However, while discussing the differences one should also not lose sight of the similarities. Therefore, it is good to approach this discussion in a systematic manner, as used in the so-called Systems Engineering (SE) method [1,2]. In line with the SE method, there are two principal functions that all hydraulic gates must perform; no matter what their operation profile is. These functions are: 1 opening and closing and 2 carrying hydraulic load. The manners in which these functions are performed can vary depending on the gate operation profile. This has generally been presented in Table 2.1. The miter gate shown in the headline of this table is an example; the introduced approach applies to all types of hydraulic gates. Table 2.1 does not specify all possible aspects of gate performance, or all optional requirements concerning those aspects. Its main purpose is to emphasize the relation between the two principal functions of hydraulic gates and the prospective project specifications. This relation can also be shown in a matrix for all particular application fields of hydraulic gates. Note that such a matrix (Table 2.2) defines in fact the gate operation profiles. Obviously, the performance levels indicated in Table 2.2 do not necessarily apply to all possible sites and projects within the listed application fields. Local conditions can always justify other choices. There also exist other application fields of hydraulic gates, like sewage processing plants, cooling systems of nuclear reactors, closures in ship lifts, submerged sites of various kinds, liquid processing industrial plants, water recreation and sport facilities, etc. These fields are not discussed in this book due to their relatively narrow character or few new features. Having distinguished the application profiles of hydraulic gates, it is good to point out that systematic approaches of this kind, including the method of SE, are not uncontroversial. They help systemizing a field of technology, but they also tend to draw attention away from specific issues in favor of issues that are common or distinguishing in such a way that it suits the systemizing. This promotes ignorance and blindness for essential issues if they do not suit the applied classification. As a result, projects are specified, contracted and controlled on a very global, so-called “functional level” (which managers understand) at the cost of keeping up with technology (which they do not). Technological expertise becomes irrelevant and undesired. Diverse experiences, for example in the Netherlands, reflect prejudicial consequences of this policy. What makes this risk still higher is that the described approach seemingly allows for running projects with less and less qualified personnel. This makes it irresistible for executive officers and mid-level managers who are under

Lock Gates and Other Closures in Hydraulic Projects https://doi.org/10.1016/B978-0-12-809264-4.00002-1

11

© 2019 Elsevier Inc. All rights reserved.

12

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

TABLE 2.1

Two Main Functions of Hydraulic Gates and the Aspects of Their Performances

1. Opening and closing

2. Carrying hydraulic loads

z y

Ry Rx

y

x

qy

G

Ry Rx

z x

P

qx

Rz

How far?

• Partly (flow control gates) • Entirely (locks, barriers, docks)

How high?

• High (locks, weirs, barriers) • Low (irrigation, flow control)

How often?

• Frequently (locks, tide barriers) • Infrequently (weirs, docks) • Seldom (barriers, bulkheads)

How often?

• Permanent (weirs, hydropower) • Frequent (locks, tide gates) • Seldom (barriers, emergencies)

What manner?

• Automatic (some irrigation, tide and floodgates) • Man-controlled (other gates)

What kind?

• Quasi-static (locks, barriers) • Dynamic (gates in flow, waves) • Both (sea locks, irrigation gates)

How fast?

• ½–6 min (locks, culverts) • 6–60 min (weirs, docks) • 60–180 min (flood barriers)

How long?

• 1–5 years (temporary gates) • 5–50 years (permanent gates) • 50–100 years (special projects)

How tight?

• No leakage (locks, docks) • Leakage (weirs, barriers)

How stable?

• Nearly constant (weirs, docks) • Variable (locks, barriers)

Under flow?

• Flow (weirs, culverts) • No flow (locks, docks) • No water (some flood barriers)

Which side?

• Upstream (weirs, docks, flood barriers, hydropower plants) • Changing (some locks, culverts)

pressure of politicians (public sector) or high-ranking executives (private sector) to cut their personnel costs. After all, complying with this pressure benefits their careers. This issue, important as it is, falls beyond the scope of this book. Therefore, the intention is now only to roughly sketch it. This has been done in Fig. 2.1. The readers are encouraged to consider it in the context of their own practice, if applicable. For the reasons as sketched above, the discussion in the following sections does not strictly follow the terminology of SE. It also does not follow the terminology of any other method that aims at classifying technological expertise rather than understanding it. Such methods are considered to be of secondary importance and will be quoted where useful and ignored where not useful.

2.2 GATES IN NAVIGATION LOCKS Navigation locks together with river weirs and irrigation systems are the fields where hydraulic gates are most widely utilized in the world. Although there are countries that do not have navigable rivers, or where such rivers are not canalized, a majority of the world’s large rivers have successfully been adapted to navigation purposes and play an important role in the transport infrastructure of their regions. While doing so, they regularly cross borders between countries, which enforce international cooperation and helps developing friendship. Good examples of the latter are the large European rivers, particularly the Danube, the Rhine and the Meuse. As indicated in Table 2.2, the gate operation profile in a navigation lock can usually be characterized by the following features: • Regarding opening and closing: entirely, frequently, usually in a mechanized manner, fast (½–6 min), watertight closing, motion normally without flow. • Regarding carrying hydraulic load: highly and frequently loaded, usually quasi-static, about 50 years of service, load in intervals nearly constant and normally on one (upstream) side. Most of these features are self-evident. Below are a number of explanatory comments:

Flow conditions

How tight?

How fast?

What manner?

How often?

How far?

1. Opening and closing

Aspects for gate specifications in their 2 functions





●

Manual ½–6 min

●

No flow No water




Under flow

Leakage allowed

●

●

●

●




●







●

●

●

●




●




●







●

●




Tide control gates










60–180 min No leakage

●




●

●

●

Flood barriers

●

●




●




●

Weir and dam gates

6–60 min

●

●

●

●

●

●




Filling and emptying devices

●

Navigation lock gates

Mechanized

Automatic

Seldom

Infrequently

Frequently

Entirely

Partly

Common levels of performance

TABLE 2.2 Global Operation Profiles of Hydraulic Gates

●

●

●




●

●




●

Shipyard dock gates

●

●







●




●

●




●

Hydropower plant gates

●

●

●







●

●

●

Irrigation gates




●




●

●




●




●

●

Continued

Emergency and service closures

2.2 GATES IN NAVIGATION LOCKS

13


●

●


●


One (upstream) Both (alternating)

Both




Variable

●

●

●

Nearly constant

●










●

●

●

Weir and dam gates

50–100 years

●

●




●

●




Filling and emptying devices

●




●

●

●

Navigation lock gates

5–50 years

1–5 years

Both

Dynamic

Quasi-static

Seldom

Frequently

Permanently

Low

High

Common levels of performance

Herein: ●: usual performance levels;
: optional performance levels.

At which side?

How stable?

How long?

What kind of?

How often?

How high?

2. Carrying hydraulic load

Aspects for gate specifications in their 2 functions

TABLE 2.2 Global Operation Profiles of Hydraulic Gates—cont’d




●

●

●







●

●

●

Flood barriers

●







●




●




●

●

●

Tide control gates

●




●

●




●

●

●

Shipyard dock gates

●

●




●




●

●

●

Hydropower plant gates

●




●

●

●




●





●




●

●

●

Emergency and service closures




●

●




●

Irrigation gates

14 2. OPERATION PROFILES OF HYDRAULIC CLOSURES

2.2 GATES IN NAVIGATION LOCKS

(a)

(c) FIG. 2.1

15

(b)

(d) Expertise and Systems Engineering—chances and risks, schematic.

Navigation lock gates always open entirely to let ships in or out; and close entirely to prevent leakage that would otherwise jeopardize the locking procedure. This does not mean that partial openings never take place, let alone that they do not need to be considered in gate design. Some types of gates, like the rotary segment gate (see Section 3.8) or vertically hinged sector gate (see Section 3.9), are also utilized to fill and empty the chamber. This proceeds by partial opening of the gate. The gates that normally do not allow this, like miter gates (see Section 3.3), can also incidentally be blocked during motion before reaching the end position. Such situations are usually seen as emergency or maintenance cases. Navigation lock gates are probably the most frequently operated hydraulic closures. The frequency of their opening and closing varies from a few to 50 and more times a day. Considering that every single closing is followed by a nearly full design load (certainly on canalized rivers), fatigue is an important issue in lock gate design. This issue is discussed in Chapter 6. High frequency of opening and closing is also one of the reasons why lock gates are normally driven by mechanical drive systems. Manual drives, regularly used in the past, are exceptional today and can only be seen on small locks for pleasure boating. Moreover, more and more mechanical drive systems are remotely controlled today. Fast opening and closing is in the first place desired by professional navigation. Although gate motion contributes less to the total locking cycle than other procedures like sailing in, mooring or filling and emptying of the chamber, it still represents a constant extension of the waiting time for ships. A glance at the photo in Fig. 2.2 leaves no doubt that

FIG. 2.2 Cargo vessels in navigation locks: (a) push tow leaving Lock 15 on the Mississippi River; and (b) ships in Terneuzen Lock, Part a: Photo USACE. Part b: Photo Beeldbank Rijkswaterstaat, Netherlands.

16

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

FIG. 2.3 Pleasure boats in navigation locks: (a) Orange Locks in Amsterdam on sunny weekends, Netherlands; and (b) boats leaving Carillon Lock on the St Anne de Bellevue Canal, Canada.

waiting is not what the captains of cargo vessels like. Both the vessels and their cargo cost a lot and every minute that those vessels do not move is a loss. Fig. 2.2 also shows the main difference in characters between the commercial shipping in America and Europe. While in America large push tow units dominate the inland navigation market, most vessels on the European waterways are separate, self-propelled barges. This substantially affects the operation conditions of locks on both continents, including the conditions of gate operation. One of the differences is that maneuvering a tow is more complex and bears potentially more risk of collision with the gate than maneuvering a single barge. On the other hand, a tow unit as pictured in photo (a) fills nearly the entire lock chamber. This means that the whole attention of both the tow crew and lock personnel can be focused on a safe passage of one particular unit, while in Europe that attention must be split, covering the behavior of many vessels at the same time. While the demand for fast lock operation comes mainly from commercial shipping, it would be wrong to say that the persons on board of pleasure boats do not mind waiting. Pleasure boating (for which in Europe “pleasure sailing” should be a better term (see Fig. 2.3) is a fast growing recreation activity in many countries of all continents. It is also a growing market of predominantly wealthy, well-organized individuals, their associations and networks. Time has its price too on that market; the idea that boaters have plenty of time is outdated. What makes things difficult to plan for is also that water recreation has its peaks and valleys, very much depending on the season and weather. In sunny summer weekends, like in photo (a), it may even be difficult to orderly handle the locking, while on other occasions the lock chambers may be nearly empty. In the first case, it is important to keep calm and follow safety rules. But it is also important that lock planners (including the gate designers) take account of such extreme conditions and make them manageable. Like in the case of commercial shipping, there is also a remarkable difference between typical recreational vessels in the European and American locks. Note that most vessels in the Amsterdam Orange Locks in photo (a) are sailing boats, while the vessels leaving the Canadian Carillon lock near Montreal are motor boats. In practice, there is a mix of both on the recreational waterways of Europe and America, but the dominating boat types are as shown on the photos in Fig. 2.3. Another feature of navigation lock gates that makes part of their operation profile is watertightness. This feature may require explanation, because it costs money to make gates watertight and a small leakage does not need to delay the locking. Such an argument against the watertightness of lock gates may sound logical but it is, in fact, misleading. Lock gates commonly need to be watertight for more reasons than only the risk of longer filling and emptying times. Here is a shortlist of such reasons: • Large leakage on one gate can prevent bringing water on both sides of the other gate to the same level. This disturbs the gate opening and exposes the locked ships to sudden flows. • Flows through narrow gaps are known to induce vibrations. Gate vibrations can hurt people, damage the machinery, upset the control system, and cause fatigue damage to the gate. • Lock gate contact surfaces (sill and quoins) can be subject to erosion due to strong leakage flows. Once started, the erosion continues decreasing the condition of the gate. • In locks between salt and fresh water basins, leakage can increase the salinity of fresh water, which brings damage to the environment, fresh water resources, and agriculture.

2.2 GATES IN NAVIGATION LOCKS

17

• Leaking flows suck debris that collects in and near the leakage gaps. This debris can damage the seals, gate contact surfaces; and disturb the opening of the gate. • Heavy leakage may cause flows in the lock chamber. These flows disturb the filling and emptying procedures and in consequence delay the locking. They can also cause unsafe situations. In gates of other operation profiles, some of these reasons may be less important. Sucking the debris is, for example, less of a problem in weir gates and no problem at all in floodgates due to their low opening and closing frequency. But it can seriously disturb the operation and bring damage to the lock gates. There is, therefore, all reason not to allow leakage on these gates. The feature that lock gates open and close without flow requires no discussion. A lock gate normally opens or closes only when the gate in the other crown of that lock is closed. There can be exceptions from this rule, for example, under flood conditions or to flush the chamber, but then the gates do not operate as lock gates any more. If there is desire for such exceptional operation, it should clearly be stated in the project specifications. Also the feature that the loads of lock gates are high and frequent seems self-evident. Yet, there is a difference between the loads on lock gates on canalized rivers and those on gates of sea locks, locks at the entrances of large lakes (like the Great Lakes in North America) or the so-called barrier locks that only operate under flood (in some cases also drought) conditions. While the gates of the canalized river locks carry more or less constant water heads by every closure, the gates of the other mentioned locks carry variable water heads. The term quasi-static describes hydraulic loads of lock gates, meaning that: • these loads are predominately static in physical sense; and • their small dynamic components can be approximated as static. The first meaning is the case with respect to differential water head which is a hydrostatic load, and hence static. The second meaning applies to wave and current loads that are physically dynamic but usually small enough and sufficiently determined to be approximated by static loads in the structural analysis of a gate. A simple model of the design loads for a lock gate can then look like the one presented in Fig. 2.4. The load model in Fig. 2.4 originates from a lock gate design for a canal with entirely regulated water levels. Therefore, the differences between the three loading cases on this figure are not large. These differences can be bigger in the locks with pool levels entirely or partly determined by natural forces. Also the two main components of hydraulic load that are shown in Fig. 2.4, differential water head and wind-induced waves, are not always the only ones to be considered. Waves, for example, can also be induced by other forces than wind. A detailed discussion on such issues is presented in Chapter 5. For the current discussion it is important to see that hydraulic loads of navigation lock gates are quasi-static. Exceptions are fatigue loads, which indeed form an important issue in the analysis of lock gates. However, the very base of this analysis, which is a single load cycle, is also modeled as quasi-static. This approach suits lock gate design very well because the gate hydraulic loads are in intervals relatively constant. More discussion on fatigue and other loads is presented in Chapter 6. The lock gate service life of 50 years is an indication only. In practice, design service lives between 25 and 75 years are common for gate structures. The required service life should commonly be defined as a period that gives the lowest total of construction costs and capitalized maintenance costs. Note that the gate service life begins on its successful

FIG. 2.4

Simple hydraulic load cases for a lock gate.

18

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

commissioning and ends on its definite scrapping, which is something else than the period of the gate uninterrupted service. More discussion on these issues is presented in Chapter 15. The features of lock gates operation profile that have been discussed until now refer directly to the two main functions of hydraulic gates. In addition, there are a number of other features that refer to what in the SE is called “aspects” of gate operation. Similar terminology and similar aspects are distinguished within the so-called RAMS methodology [3]. In the case of navigation lock gates, the aspects that ought to be considered are: • • • • • •

reliability and availability; safety; managing and maintenance; esthetics and environment; manufacturing and installation; and service life and demolition.

The last aspect, service life, has already been distinguished as a feature of the second main function: carrying hydraulic load. In effect, the service life aspect is doubled. The reason for this doubling is that the gate service life can also be determined by other factors than the loading. Such factors are, for example: corrosion and material aging, deliberate or enforced lack of maintenance, temporary character of the lock or its gates, technological aging, historical value of the site, war damage and other disasters. These factors are too diverse and too complex for a comprehensive presentation, but their selected issues will be discussed in appropriate chapters. Reliability is defined as the probability that something, in this case a lock gate, will perform the desired function under given conditions and in a given period of time. Availability is defined as the capability of something, in this case a lock gate, to be ready for performing the desired function under given conditions and in a given period of time. Leaving the exact distinction between these terms to academics, we can summarize it by saying that a reliable gate is the one that does not fail; and an available gate is the one that is there when it is needed. It should be beyond doubt that lock gates must have both of these features. Also the safety of hydraulic gate operation is a feature of utmost importance. In the RAMS considerations, safety is defined as being free from excessive risks and causing no injuries. Yet, it is good to realize, that various participants and stakeholders in a navigation lock project usually have different priorities regarding safety. An example is the issue of ship collision that can be solved by providing the gate with an energy dissipation device or by aiming for energy dissipation in the ship itself. In the first case, the gated closure suffers the damage; in the latter case—the ship. Nevertheless, a glance at photo (a) in Fig. 2.3 leaves no doubt that safety is a requirement of significant importance in navigation lock gates. Such gates must also be manageable and as easy to maintain as possible. By manageable, we mean controllable by simple, standard procedures and handlings. An example of a poorly manageable gate is the buoyant concrete gate of the GIWW closure in the New Orleans’ Inner Harbor Navigation Canal. It requires many personnel, additional equipment, part of it stand-by, and a long time to close it correctly, which is discussed in more detail further. This situation is acceptable only because it concerns a flood barrier gate of a low opening and closing frequency. Similar solutions are quite unacceptable in navigation locks. Maintainability is a feature that can be seen as a separate aspect but can also be considered as a necessary condition for other aspects, like reliability or availability. That gates need maintenance is self-evident. Lock gates require it more than the gates of most other application profiles. The reason for that is a more intensive operation with frequent and short openings and closings, leaving no time for malfunctioning, stagnations, multiple trials and the like. For the same reason the maintenance of lock gates should be performed in a systemized manner. The discussion on various maintenance systems and the related activities is presented in Chapter 15. Esthetics and environment are aspects that may not directly affect the gate operation, but they codetermine the quality of the surrounding. In the case of esthetics, that “surrounding” can be understood in a narrow sense, referring to the area that lies more or less within the observer’s horizon (disregarding image transmission possibilities). In the case of environment, the impact can be wider. Sometimes, like in regard to energy consumption or the use of unsustainable materials and technologies, that impact, although small, may even be global. See Chapter 12. Manufacturing and installation are aspects that primarily refer to the construction stage of a gate project. It is obvious that a correct design must take account of these aspects. The question that the designer should answer is not only whether the designed gate is capable of being manufactured, but also whether it can be manufactured efficiently, in high quality and in a healthy and well-controlled manner. The same applies to the transport and installation procedures. In the case of lock gates, their designers or manufacturers should also deliver detailed documents and guides enabling safe periodic removals of the gates, their maintenance and repair, transport and subsequent new installation. A navigation lock gate normally undergoes these procedures about 6–12 times in its service life.

2.3 FILLING AND EMPTYING DEVICES

19

2.3 FILLING AND EMPTYING DEVICES The main field of application for filling and emptying devices is navigation locks. Therefore, the operation profile of filling and emptying gates and valves is in this section focused on their operation in locks. It should, however, be noted that such devices also operate in some other kinds of hydraulic sites. Here is a list of the most common kinds of sites that utilize filling and emptying devices: • • • • • • •

navigation locks; dry docks in shipyards; pumped-storage power plants; floodwater storage basins; basins of constant water level for navigation purposes (e.g., Gatun Lake in Panama); sewage processing plants; and large cooling systems and liquid treatment basins (e.g., in Fukushima Power Plant, Japan).

As filling and emptying devices are primarily applied in navigation locks, it should not surprise that their operation profile shows similarities to that of the lock gates. Table 2.2 gives the following global operation profile for the gates and valves in filling and emptying systems: • Regarding opening and closing: entirely, frequently, usually in a mechanized manner, fast (½–6 min), watertight closing, motion often under flow. • Regarding carrying hydraulic load: low or moderate but frequently loaded, dynamic when under flow, 5–50 years of service, load predominately variable and normally on one (upstream) side. Most of these features are self-evident or have already been explained when discussing the operation features of lock gates (see preceding section). Below are a few additional comments: Entire closing is obvious, but entire opening is not always the case in filling and emptying devices. There can be situations when partial opening is favored, for example when slow flows in the chamber help locking special vessels or are desired for other reasons. The frequency of opening and closing is normally the same as for lock gates. This makes it necessary to consider fatigue loads in the design. An additional reason for this is the phenomenon of so-called “cavitation,” discussed further. It generates large and instable additional pressure differences on both sides of the gate or valve, which causes fatigue both directly and indirectly (by inducing vibrations). For the same reasons as in lock gates, filling and emptying devices are mostly mechanically driven, while a limited number of them, usually in small locks on pleasure boating routes, utilize manual drives. The opening and closing times are slightly shorter than those for lock gates, commonly ½–2 min, which results from shorter travel distance. This distance and the lower gate mass make the filling and emptying devices better suitable for hand operation, but once the lock gate movements are mechanized it is convenient to do the same with the filling and emptying valves. Filling and emptying of a lock chamber can be arranged in three ways: • Through lock gates: Gates of some types (like vertically hinged sector gates) can partially be opened to allow for water flow into or out of the chamber. • Through culverts: Culverts are closable conduits that enable filling and discharging the chamber while bypassing the actual lock crowns. • Through openings in gates (such as rolling gates or miter gates): Such openings must close to hold water in or outside the chamber—and open to allow for chamber filling or discharging. The first arrangement does not require separate filling and emptying devices; the second and the third arrangements do. Obviously, the boundary conditions for the design of such devices are not the same in culverts and openings in gates. Main differences and specific requirements are presented in Section 3.17 and Chapter 10. Culverts are usually preferred in large locks, because they give a better flow distribution, allowing for faster filling and emptying. Openings in gates cost less but they generally give more concentrated and stronger flows that require better mooring and more care by vessel crews. The filling and emptying process proceed slower for this reason. These preferences can be observed in Fig. 2.5 that shows examples of both arrangements. For a good comparison, both examples are from the same country and they both utilize vertical lift valves with rack and pinion drives as filling and emptying devices. The culvert valves in photo (a) operate in the Hansweert Lock, where they also make part of the salt and freshwater separation system. Chambers of this lock are 280 m long and 24 m wide. The gate valves in photo (b) operate in the new Juliana Lock in Gouda that has a 115 m long and 14 m wide chamber. Taking also the average

20

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

FIG. 2.5 Filling and emptying valves in culverts and lock gates: (a) Hansweert Lock and (b) Juliana Lock in Gouda; both in the Netherlands. Photos Rijkswaterstaat.

differential water heads into account, the Juliana Lock chamber discharges per locking about 10% of the water volume that the Hansweert Lock chamber does. This range of difference is also visible in the sizes of filling and emptying devices in both locks in Fig. 2.5. In photo (a), the spare vertical lift valves are shown in the background; behind one of their operating drive units. In photo (b) the valves are shown at the bottom, in a dry chamber shortly after the gate installation. Nevertheless, the discussed relation between lock chamber sizes and preferred filling and emptying arrangement should only be seen as an indication. There can also be reasons for providing a small lock with culverts or a large lock with valves in the lock gates. An example of the latter is the 70-m wide new IJmuiden Sea Lock in the Netherlands that will be under construction when this book is published. It is going to be the widest navigation lock in the world. The reason for choosing for filling and emptying through the lock gates was in this case the shortage of space [4]. Watertight closing is normally required for filling and emptying devices for the same reasons as in the case of lock gates. What does differ from the lock gate operation profile is that filling and emptying devices must always be designed for operation under flow, while lock gates move usually (exceptions notwithstanding) only without flow. This generates a number of additional concerns and requirements regarding particularly the risks of vibrations, cavitation, so-called “hydraulic rollers,” sucked ice and debris, air drawn into culverts and the like. The designers of filling and emptying devices must pay attention to these issues. In this context, it is important that the designers and their customers clearly agree whether the filling and emptying devices are indeed only going to be used for filling and emptying. If so, than other use should definitely be ruled out. If not, that the conditions of the other use must be specified and secured by appropriate design measures. It unfortunately often happens that this issue is ignored: The lock owner begins to use his filling and emptying devices also for flushing the chamber or discharging excess water and then sees them vibrating. One should realize that the operation conditions are then different than on regular locking. The device closures operate in constant, long-lasting flow and are often only partially open. This is unfavorable in view of vibrations—not to mention other risks. The loads of filling and emptying gates and valves are usually low or moderate but relatively frequent. The term “low of moderate” is relative here and refers to total load, that is, not the load per surface area because that load is as high as on the lock gates or even slightly higher. The surfaces of filling and emptying devices that are exposed to hydraulic loads are relatively small. In contrast to lock gates that have been classified as quasi-statically loaded, the loads of filling and emptying devices should be seen as predominately dynamic. The reason for this is not that these loads cannot be modeled as quasi-static. They can, and it is sufficient for some considerations. The reason is that filling and emptying devices operate predominately under flow, which is a condition requiring dynamic approach. The details of this approach are presented in Chapter 10. The next feature of filling and emptying devices operation profile, their service life, has been set in the range of 5–50 years, which is lower than for lock gates. There are two reasons for that: • Relatively small size and by that an easy replacement of these devices. This counts less at the sites where size, ease of replacement and transport present a minor problem. • More exposure to fatigue due to dynamic operation conditions (flow). It may then be economical to construct lighter at the cost of earlier fatigue damage and shorter service life.

21

2.4 MOVABLE CLOSURES OF RIVER WEIRS AND DAMS

These considerations can, however, be different in a particular project. Choosing an equal service life for both lock gates and filling and emptying devices is not a mistake too. After all, there exist culvert valves, like those in the Chittenden Locks in Seattle, USA, that approach 100 years of service life.

2.4 MOVABLE CLOSURES OF RIVER WEIRS AND DAMS The group of movable closures on river weirs covers here gates in dams with high spillways and gates in weirs with relatively flat bottoms. In both cases, the purpose of gated openings is to control the flow and the upper pool level. The lower pool level is normally controlled by another dam or weir located at some distance downstream the river. As the tasks of gated openings are in both cases similar, so are also the structures of the gates. Fig. 2.6 shows the cross-sections of such gates in their vicinities on a dam spillway (a) and in a weir with a relatively flat bottom profile (b). The presented examples refer to operating sites in, respectively, the Columbia River in the USA and the Danube River in Austria. Similar as they are, the gate operation profiles are not quite identical in both cases. There can be some different preferences concerning the details and depending on the type of applied gate. For example, in radial gates, as pictured in Fig. 2.6, it is more common to let the flow take place under the bottom edge in spillway closures (a) and above the top edge in river weirs (b). This is, however, not a strict design rule; the opposite arrangements have successfully been practiced too. There also exist a few other minor differences between both cases from Fig. 2.6, including more frequent applications of top flaps in case (b). Such differences are discussed in appropriate other chapters of this book. The only major difference in gate operation profile between case (a) and (b) is that the entire reverse side of a spillway gate is usually “dry,” while that of a river weir gate remains partly submerged. This has substantial influence on the behavior of some gates, which is also discussed further. For the current discussion, however, it is relevant that to conclude that the similarities of both cases predominate and justify their classification into a common gate operation profile. As indicated in Table 2.2, the following features can usually characterize this operation profile: • Regarding opening and closing: partly, infrequently, in a mechanized or even automated manner, slow (1 h or longer is not exceptional), low watertightness, usually under flow. • Regarding carrying hydraulic load: highly and permanently loaded, usually quasi-static, service life 50 years or higher, load usually nearly constant and always on one (upstream) side. Most of these features are self-evident. Below are a few explanatory comments with respect to some of them. The term “weir gates” refers from now on for short not only to the closures of “classic” river weirs, but also to those of dam spillways. Since the purpose of weir gate operation is the control flow and upper pool level, its normal operation position can only be partly open. The entirely closed position is also practiced, but in that case the active control of flow and water

HWL +174.19

Gantry crane

+175.39 Columbia River

Danube River

Spillway pier

Service bridge

Radial gate Trunnion girder

Trunnion girder

Trunnion CL + 162.46 Max. TWL + 160.75

TWL +251.00

+252.50

Weir pier

Crest +153.92

+246.40 Bulkhead slot

Deflector

TWL +241.59 Damping basin

Normal TWL + 146.76

+232.00 Apron sill Base +137.16

(a)

Inspection tunnel

33.53 (monolith)

+138.99

21.03 (apron)

(b)

Radial gate with top flap

Inspection tunnel

TWL = Target water level

FIG. 2.6 Typical arrangements of gated openings in dam spillways and river weirs: (a) Columbia River Wanapum Dam, Washington State, USA, source: Grant County PUD; and (b) Danube Freudenau Weir in Vienna, Austria, source: Verbund Hydro Power GmbH.

22

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

FIG. 2.7 Double lift gates of the Belfeld Weir on the Meuse, the Netherlands, raised to pass flood. Photo Rijkswaterstaat.

level is performed on other gates in a weir. Entirely opening the gate is only practiced in case of flooding, other emergencies or maintenance on the site. The latter requires the closing of the opening by other means, like stoplogs or bulkheads. On some American waterways, in particular the Ohio River and Illinois Waterway, wicket gates are utilized. These gates allow run of the river even during flood conditions. They are only opened during drought periods to help maintain pool levels in the river. One unique feature of wicket gates, including the newly constructed gates in the Olmsted Dam, is that they are manually operated. For more details, see the discussion on wicket gates in the next chapter. The entire opening of weir gates by flooding is an extreme measure. In Europe, it is usually practiced in areas around deltas, confluences or other discharges of rivers, like in the Netherlands (Fig. 2.7). In the higher located upper river courses, like South Germany or France, such a measure is used less frequent as it abandons any form of floodwater control. In America, the entire opening of weir gates is under flood conditions also practiced in the mid courses of rivers. The feature that weir gates are moved infrequently results from the relative stability of river flows that do not vary much on daily basis. The mechanized and on a growing number of sites automated manner of gate movements does also not surprise considering their sizes and weights. Slow movements are the result of both relatively slow variations of river flows and the great predictability of those flows thanks to the modern hydrological models and measuring systems. In contrary to, for example, lock gates, there is not much need to make weir gates watertight. From the reasons that have been listed for lock gates (see Section 2.2), only two also apply to weir gates. These are the risk of vibrations and erosion of contact surfaces. The other risks, including local damage by sucked debris, are smaller due to the infrequent gate movements, short distances of these movements and the commonly high robustness of the gates, their drives and contact areas. Nevertheless, the issue of vibrations requires a very thorough consideration in weir gate design. One reason for this is the long periods of operation under nearly constant flows, which gives the structure a long time and a range of potential conditions that can induce vibrations. The probability that one of the structure natural frequencies is locked into the so-called vortex-shedding frequency of the flow is then high. The same applies to other flow-induced phenomena, like the pull-down forces, vacuum build-up under poorly aerated flow nappes and risk of their implosions and cavitation of contact areas. See Chapter 6 for more discussion on these matters. Yet, presuming that measures have been taken to prevent vibrations, hydraulic loads of weir gates can be characterized as quasi-static, high and nearly permanent. This is also how engineers commonly approach the analysis and design of such gates. After all, it is for many reasons better to have an economically constructed gate that is not supposed to vibrate, than to have a heavily constructed gate that may vibrate but is strong enough to sustain it. This strategy requires, however, a far-sighted vision that covers all possible conditions of gate operation. There have been, for example, weir gates that started to heavily vibrate after some years of satisfactory operation. One reason was an obstacle on the sill that made the closing incomplete leaving a gap for a turbulent flow [5]. Like in case of lock gates, the weir gate service life of 50 years and higher represents a common but not necessarily binding indication. Also for weir gates, the target service life should commonly be assumed as a period that gives the

2.5 FLOOD, TIDE, AND RETENTION GATES

23

lowest total of construction costs and capitalized maintenance costs. The weir gate service life begins, like for a lock gate, on the day of putting into service after successful commissioning, and ends on the day of the definite removal for scrapping. The project specifications should also define the minimum period of gate uninterrupted service under normal conditions. This period is a crucial parameter for determining the frequency of inspections and maintenance. The detailed discussion on these matters is presented in Chapter 15. In addition to the features derived from the two main functions of weir gates, there are a number of other features that such gates should have. As already discussed for lock gates (see Section 2.2), these features are classified into “aspects” in the Systems Engineering approach. Similar terminology and similar aspects are followed within the so-called RAMS methodology [3]. The list of these aspects and the discussion of operation features that should cover them are roughly the same as discussed for the lock gates and do not need to be repeated here.

2.5 FLOOD, TIDE, AND RETENTION GATES The operation profile of floodgates differs substantially from that of lock and weir gates. There are two main reasons for this difference: • Different objectives: The purpose of lock and weir gates is controlling the water levels on inland waterways. The purpose of floodgates is, as the name says, preventing the intrusion of flood or storm surge waters into the hinterland. • Different operation frequencies: While lock and weir gates are normally in permanent operation, floodgates are normally in stand-by condition. Their operational closing proceeds sporadically in the frequencies varying between a few times a year to once in a few years. For the sake of simplicity, we disregard here the structures that combine both functions. There exist lock and weir gates that also operate as floodgates when the need arises. In that case, the operation profile combines the features of both categories of gates. This should, obviously, proceed in a way that satisfies the requirements of these categories. As indicated in Table 2.2, the following features can usually characterize the gate operation profile in a flood barrier: • Regarding opening and closing: entirely, seldom, usually in a mechanized manner, slow (nearly 1 h or longer), no watertight closing, moved without or with little flow. • Regarding carrying hydraulic load: highly but seldom loaded, predominately quasi-static, 50–100 years of service, load highly variable and normally on one (upstream) side. An application field of floodgates that does not comply with all features of this operation profile is tide control. Yet, tide gates show many similarities with floodgates, they originate from the same idea—keeping water away, and they very often combine the functions of tide control and flood defense. This is also the reason why they are included in this section. Nevertheless, the operation profile of tide gates deserves a separate note. According to Table 2.1, it includes the following features: • Regarding opening and closing: entirely in most cases, frequently, in a mechanized or automated manner, mid-fast (10–30 min.), no watertight closing, moved often under flow. • Regarding carrying hydraulic load: highly and frequently loaded, predominately quasi-static, 25–50 years of service, load variable but in comparable cycles, normally on one (upstream) side. Finally, there is a category of closures that have a reverse task to that of flood and tide gates. These gates do not keep water away but they keep it in; such closures are called retention gates. Their main fields of application are in reservoirs for the storage of drinking water, artificial lakes for irrigation, environmental purposes, cooling, and firefighting, reservoirs in hydropower plants, process industry and sewage processing plants. They can also be used to help maintaining inland waterway levels in periods of droughts. In the latter case, their operation profile shows similarities to floodgates, although the resulting hydraulic loads are usually lower. In the other cases, the diversity of application requirements makes it impossible to speak of a common operation profile. Their inclusion in this section is, therefore, a rough approximation. The reader is advised to critically check the required operation features. Some of the features summed up for flood, tide and retention gates are self-evident. The comments below refer to the features that are not unquestionable or may need to be clarified. Entirely opening and closing is not questioned for floodgates, but it evokes discussion for tide gates. Tides, after all, operate in frequent and very regular water flows that form a natural environment for many spices of plants and animals. This applies to a much lesser degree to floods. Although floods too can be seen as an inherent component of

24

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

FIG. 2.8 Tide and floodgates without and with openings: (a) Cardiff Bay Barrage, United Kingdom and (b) Qinhuai Barrier in Nanjing, China.

natural environment, their impact is generally considered violent and disastrous, exceptions like the annual floods of the Nile notwithstanding. Therefore, floodgates will commonly be designed for entirely closing, while in tide gates this feature depends on the location. Tide gates that close harbor docks or help keeping urban areas dry are usually designed to close entirely. On the contrary, gates in the mouths of tidal rivers, particularly in the areas of rich habitat, are more and more often designed to close partly. The latter can also be realized by providing tide gates with closeable, often automatically regulated openings for fish passage and low flows to maintain the desired salinity of tidelands. If a gate also performs retention functions, such openings can help maintaining the desired upstream water level. Examples of gates without and with additional openings are presented in Fig. 2.8. In both examples, the gates operate as barriers and tide control closures. The Cardiff Bay sector gates, one of which is shown in photo (a), substantially stabilize the water level in the bay despite the high tidal range in the mouth of the Severn River. They are 16 m high and they operate in three parallel barrier locks, each 10.5 m wide. Note that the Cardiff Barrier (locally called “Cardiff Barrage”) also comprises a number of sluices. Moreover, the gates installed are vertically hinged sector gates, which can very well open and close under flow or even stay partly open under flow for some time. Therefore, there was no need to provide additional openings in these gates. The Cardiff Bay is also not a basin of particularly high environmental importance, nor does it facilitate extensive agriculture. Also this makes the issues like water level and salinity control less critical. These conditions are in many respects opposite for the Qinhuai Barrier in Nanjing, shown in photo (b). That barrier comprises two so-called visor gates (also called “arch gates” by some authors), which are horizontally hinged and perform not as well as the vertically hinged sector gates when partly opened. See discussion on such issues in the next chapter. Another difference is that the Nanjing Barrier is not equipped with separate sluices. Yet, the Qinhuai River discharges to the Yangtze River that still has tidal character at that location and the salinity of its water equals about 1% on average. In addition, the Qinhuai River is a feeder of the so-called “paddy-fields”—a popular form of growing rice. Paddy fields still cover most of the river basin area South of Nanjing, although the urbanization and industrialization of recent decades significantly disturbed their ecosystem [6]. The Qinhuai River plays also an important cultural, historical and economical role in the city of Nanjing with its over 8 million inhabitants (2015). There was, therefore, all reason to provide the barrier with adjustable openings. The designers have chosen to do it in the upper fields of the gates, as shown in the photo. This also allows for maintaining the desired water level of the Qinhuai River in periods of drought, in which case the tide gates operate as retention closures. The reason why operating frequencies of floodgates have been classified as low, and those of tide gates as frequent, is quite obvious: floods happen much more sporadically. In both cases, however, the prevailing operation manner is by an electrically powered mechanical device. Manual drives are, in general, not fit for this purpose considering the high drive forces required. Yet, the slow operation (mid-fast for tide gates) allows for high gear ratios and relatively low power drives, which is discussed in more detail further. It also needs no explanation that some leakage can normally be accepted on gates of flood and tide barriers. Another issue is, however, operation under flow. Modern forecasting methods, supported by satellite and other data make it

2.6 GATES IN HYDROELECTRIC PLANTS

25

today possible to predict floods with great accuracy a number of days in advance. This, in turn, gives the public services or agencies in charge enough time to close the flood barriers at the most convenient moment, that is, without or with little flow. Therefore, floodgates do not commonly need to be designed for opening and closing under flow. Tide gates, however, can better be designed for closing and opening under flow. There are two main reasons for that: • The so-called “slack water,” that is, the time that the tide flow entirely ceases, is usually quite short and can to some extent be affected by weather conditions. This gives very narrow tolerances for closing and opening of the gates. • The frequency of operational closings and, as a result, their total numbers in the gate service life are for tide gates a magnitude higher than for floodgates. So is also the probability of failure. Another difference between flood and tide gates concerns the character of hydraulic loads. In both cases, these loads can be considered high, although extreme floods usually result in higher loads than tides. More substantial is the difference in the load occurrence frequencies: seldom (once in a few years) in floodgates and frequent (up to four times a day) in tide gates. This means that the drives of floodgates will very seldom be put to work and the only fatigue loads can be induced by waves. In tide gates, however, the drives will very regularly operate and the dominant fatigue load will likely comprise the entire differential water head. These are issues of crucial importance that lead to quite different designs and maintenance programs for gates of both operation profiles. Regardless of its frequency, the load can in intervals be considered as quasi-static in both cases. Such an approach is typically also the first step to the fatigue analysis that, as such, is a dynamic issue. The desired service lives, usually 50–100 years for floodgates and 25–50 years for tide gates, do not differ much. The reason why tide gates will often have a slightly shorter service life is their fatigue and the commonly smaller sizes, easier transport and installation, when compared to floodgates. The operation loads of floodgates, infrequent as they are, are highly variable. Those of tide gates are also variable but to a lesser extent, as there is normally more regularity in tides than in flood levels. The most feared in coastal areas are the combinations of so-called spring tides and heavy storm surges. It was such a combination that on February 1, 1953 caused a disastrous flooding of large parts of the Netherlands, England and Belgium costing about 2500 lives, most of them in the Dutch province of Zeeland. In order to prevent it from happening again, large flood barrier projects were carried out in these countries, like the Eastern Scheldt Storm Surge Barrier in the Netherlands and the Thames Barrier in London, UK. The gates of these barriers are discussed in more detail later. An illustrative example for the current discussion on flood gate loads is the design load specification for the Hartel Canal Storm Surge Barrier near Rotterdam, the exact location of which has been shown in Fig. 1.10. The most essential design cases of hydraulic loads are schematically drawn in Fig. 2.9 [7], along with a global three-dimensional sketch of the barrier. Observe that the Hartel Canal Barrier does not quite comply with the earlier discussed feature that floodgates are commonly designed for entire closing. Its closing is: • entire in the sense that the whole available skin plate is engaged in closing; and • partial in the sense that in does not close the entire cross-section of the flow—it allows for both overtopping flow and underflow. In this case, no environmental or agricultural reasons determined such a choice. The real reason is that the defended land can receive certain volumes of floodwater; and making use of this has a favorable, damping effect on the storm surges in harbors on the undefended side. Such an approach requires, however, a very thorough design of the gates in flow and an equally thorough control of the closing and opening procedures. The latter must, for example, take account of the reverse flows after the storm. The quasi-static load figures resulting from an extreme storm (once in 10,000 years), “normal” storm (once in 100 years) and the extreme reverse flow before opening are respectively presented in sketches (b)–(d) in Fig. 2.9. More discussion on hydraulic loads of floodgates, including the detailed determination of design loads for the Hartel Canal Barrier, is presented in Chapter 5 of this book.

2.6 GATES IN HYDROELECTRIC PLANTS Hydroelectric plants utilize hydraulic gates at different locations within a plant and for a number of different functions. One of such locations is in spillways of dams that maintain the desired water levels of upstream pools. The main

26

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

FIG. 2.9 Hydraulic design loads of the Hartel Canal Storm Surge Barrier [7], the Netherlands: (a) global 3D sketch of the barrier; (b) quasi-static hydraulic load from extreme 104 storm; (c) quasi-static hydraulic load from “normal” 102 storm; and (d) quasi-static hydraulic load from reverse flow before opening after the storm.

function of these gates is to discharge the excess flow that is not used to move the turbines. The gate operation profile is then identical to the profile of gates in dam spillways that do not necessarily facilitate electricity production. This case has already been discussed in Section 2.4. The other locations include so-called intakes, penstocks, high-line conduits and diversions. All these terms are explained in Section 3.17.3. Hydroelectric plants can be arranged in various ways. They can also employ various types of turbine-generator units bearing usually the names of their inventors, like Kaplan, Francis, Pelton, or Bulbo. Such units set different conditions for their driving flows; and can be situated vertically, horizontally, or in an inclined position. All these possibilities result in a wide range of operating conditions for the gates that control the flows in hydroelectric plants. An impression of the variety of water conduits in such plants gives the general layout drawing of the Hoover Dam Power Plant on the Colorado River in the USA (Fig. 2.10), probably the most famous hydroelectric plant in the world. The drawing shows the as-built situation of that plant shortly after construction in 1936 [8], including some revisions conducted in the 1940s and 1950s. Water conduits are inclined hatched. All these conduits are in one or the other way gated, sometimes at their inlets as well as the outlets. One type of these gates, the so-called Stoney gates of the dam diversion tunnels, will be presented in more detail in Section 3.17.3. The wide range of operating conditions in the gates of hydropower plant conduits makes it somewhat difficult to define a common operation profile for these gates. Therefore, the features specified in Table 2.2 for these gates should be seen as a rough indication. Below is the summary of these features: • Regarding opening and closing: partly, infrequently, in a mechanized and often automated manner, mid-fast, watertightness seldom required, gate movement nearly always under flow. • Regarding carrying hydraulic load: loads high, nearly permanent and predominately dynamic due to the flow, 25–50 years of service, load highly variable and always at one (upstream) side. The operation in partly opened position has the same reasons as for weir gates; it is inherent in flow regulation. The same applies to the mechanized, often automated character of gate movements. These movements are, however, slightly more frequent and their velocities are, normally higher than for weir gates, despite the nearly identical character of upstream flow. The main reason for that is the very presence of turbine-generator units, which require more flow control, flow redirection from one unit to another, for example for maintenance purposes, and a better fine tuning

2.6 GATES IN HYDROELECTRIC PLANTS

FIG. 2.10

27

Hoover Dam Power Plant, plan and section of the plant and its gated water conduits [8].

of that flow. In addition, the flow velocities through hydropower wicket gates (different than the wicket gates mentioned in Section 2.4, see also Fig. 3.255) are extremely high. Note that the Hoover Dam Power Plant from Fig. 2.10 has two main penstocks, each 9.14 m (300 ) in diameter, running from the intake towers at either side of the river. These main penstocks feed eight side penstocks, each 3.96 m (130 ) in diameter, which carry water to the turbines. This sets the total number of turbine-generator units at 17, as the last penstock on the Arizona side feeds two smaller units. Not all of them will simultaneously operate at full power, so the hydraulic closures in these and other conduits have indeed much work in distributing the flow. One might suppose that the reason for the latter is the size of this facility. The Hoover Dam Power Plant was the world’s largest at the time of its construction and it still belongs to the largest plants of this kind in America. The gate operation in small hydroelectric plants is, however, not much different, except for the scale. In Fig. 2.11, a row of turbine-generator units of the Hoover Dam Power Plant has been compared to a row of such units in a Lesna Power Plant in Poland, which is the oldest operating hydroelectric plant in that country and one of the oldest in Europe. Both

FIG. 2.11 Turbine-generator units (here of the Francis type) in a large and small power plant: (a) Hoover Dam Power Plant, USA and (b) Lesna Power Plant on the Kwisa River, Poland.

28

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

plants employ turbine units of the Francis type; the Hoover Dam Power Plant (a) in a vertical position (therefore only the generators are visible) and the Lesna Power Plant (b) in a horizontal position. The power difference of single units is enormous: about 133 MW in the Hoover Dam and a little more than 0.5 MW in the Lesna Plant. Yet, also the second plant comprises a number (here 5) of units, while it has technologically been possible, also at the time of its construction (1901–1906), to receive its total power in a single, larger turbine. The main reason for this is visible on the photo. Note that the generator of the turbine unit no. 3 has been removed for major maintenance. Yet, the remaining operational units still deliver the desired power. The last two features of gate movements in hydroelectric plants, operation (closing and opening) under flow and no need for watertight closing, are self-evident. The latter applies with the reservation that the flows of leaking water cannot induce vibrations. The discussion of this issue is for the gates in hydroelectric plants basically the same as for weir gates (see Section 2.4). The same applies to the features that describe the character of hydraulic loads on power plant gates. A significant difference with weir gates is only that the variety of gate locations and the resulting design loads is in hydroelectric plants slightly higher than in river weirs or dam spillways. This has already been pointed out at the beginning of this section. Not surprisingly, also the developments and lessons learned in both application fields are largely shared by specialists. An example is the construction of an auxiliary 6-gated spillway of the Folsom Dam in California, with radial gates located at the foot of the dam instead of at its crest. This decision, known as the so-called “low and slow” solution was taken in the aftermath of the 1995 gate failure atop the spillway of that dam. The details of this are presented in Section 3.6.3.4 and in Chapter 16. For the current discussion it is relevant, however, that the “low and slow” solution is not new. It is, in fact, a standard, well-proven arrangement in the diversion conduits of hydroelectric plants. Like in the case of weir gates, there are still a number of other features that the gates in hydroelectric plants should have which do not directly follow from the two main functions of these gates. These features are classified into “aspects” within the methodology of SE, RAMS [3] and the like. The list of these aspects and the discussion of features that should cover them are roughly the same as discussed for the lock gates (see Section 2.2), while the priorities may slightly vary due to the different tasks of gates in both application fields.

2.7 GATES IN HARBOR AND SHIPYARD DOCKS Docks in harbors and shipyards are often constructed with gated accesses. This applies to nearly all docks (dry, wet, floating, etc.) in shipyards that must provide dry work conditions on those parts of vessel hulls that are normally under water. However, it also applies to many docks in harbors. The main reasons for that are tides and storms in sea harbors; and floods (sometimes droughts) in inland harbors. A common arrangement in gated docks of sea harbors is to maintain water at the high tide level, which ensures that the vessels will stay afloat at low tide as well. A common arrangement in the gated docks of inland harbors is to let water follow the inland waterway level; and to close the gates only in case of flood, drought, ice passage or other extraordinary conditions. Dry docks in shipyards only need to be filled to let the ship out; and in repair docks also to let her in. There are normally no intermediate filling and emptying procedures. The frequency of gate opening is, therefore, very low and there is time enough to do it at the most convenient moment, for example at high tide. These conditions can be different in harbor docks that need to be accessed and left by more vessels at different times and under various differential water heads. Therefore, a single gated access will usually be a satisfactory solution in a shipyard dock, while an access to a harbor dock or terminal will often be provided with a lock. There are, however, exceptions to this rule. As indicated in Table 2.2, the following features can usually characterize the gate operation profile in shipyard and harbor docks: • Regarding opening and closing: entirely, seldom, in a mechanized manner, very slow (about 1 h or longer), watertight closing, gates normally moved without flow. • Regarding carrying hydraulic load: high and nearly permanent load, predominately quasi-static, 25–50 years of service, load in intervals nearly constant and commonly on one side. Shipyard and harbor dock gates always open entirely to let the vessels out or in. Then they also close entirely to prevent the leakage that would otherwise disturb the work in the dock. The filling of the dock usually proceeds through gated culverts, in a way similar to navigation locks. The difference is that the dock filling may normally last longer. Like in locks, it is never possible to entirely equalize the water levels in and outside the dock by gravitational

2.8 IRRIGATION GATES

29

FIG. 2.12 Gate of St. Nazaire L. Joubert Dock, France: (a) attacked by HMS Campbeltown in 1942, source: www.libertyship.be and (b) with MS France under construction in 1960.

flow alone. The last decimeters of the differential water head can, if required, be removed by pumping, but most dock gates are designed to open under small (0.10–0.20 m) residual water head. The movements of dock gates are seldom (once in a few weeks to a few times a day) in harbor docks; and very seldom (range of once or twice a year) in shipyard docks. In the latter case these movements are determined by the construction or repair cycle of a ship, offshore rig or another vessel. That cycle can be long. For example the world’s largest cruise ship at the time of writing this book, MS Harmony of the Seas, was built by STX France in more than 2.5 years, the most of which time she occupied the Louis Joubert Dock in St. Nazaire. This is the famous “Normandy Dock,” also known from a brave action of British frigate HMS Campbeltown in World War II. Fig. 2.12 shows an artist’s impression of this action and the repaired gate during construction of the French liner MS France in 1960. The closing of dock gates should in both cases be watertight: for the shipyard docks to provide dry working conditions and for the harbor docks or terminals to maintain a stable inner water level. In the latter case, an additional reason is often to limit the salinity. There can still be more reasons for limiting the leakage (see the shortlist of such reasons in Section 2.2). Undesired as it is, some leakage will happen anyway. For this reason and in order to remove rainwater, shipyard docks normally have a drainage installation with one or more pump units that keep the dock floor dry. The combination of large sizes and seldom movements is the main reason why the gates of shipyard and harbor docks are opened and closed mechanically and relatively slowly. These gates can, like in the L. Joubert dock, have their own recesses and tracks or hinges at the dock entrance, in which case we will speak of fixed gates; or they can moor in the neighborhood to be floated into the dock entrance when desired, in which case we will speak of free gates. The discussion on various arrangements and structural systems of dock gates is provided in appropriate sections of the next chapter. Dock gates are normally opened and close without or with a negligible flow. The feature that the loads on dock gates are high and in intervals rather stable requires no comment. The frequency of these loads is, like the frequency of opening and closing, very low in shipyard docks and medium to low in harbor docks or terminals. The gates in harbor docks will also not necessarily carry their high design loads at every closing, while the probability that the gates in shipyard docks will do it is higher. This too is a direct consequence of different operation frequencies. In both cases, however, the hydraulic loads can largely be considered quasi-static and approximated by hydrostatic pressure figures in the way similar to that for lock gates (see example in Fig. 2.4). The design service life of usually 25–50 years is also comparable to that for lock gates. Other features of dock gate operation profile, like the ones that result from the RAMS aspects and SE criteria, are similar to what has already been discussed in the preceding sections of this chapter. The differences concern only some priorities and mainly result from the risks involved. It should be obvious, for example, that the RAMS aspects “Reliability” and “Safety” require especially much attention in shipyard docks, where many people are at work and the gates are normally within the reach of heavy cranes. However, also the situations in locks to large marinas (like in Fig. 2.3A) can occasionally evoke safety concerns.

2.8 IRRIGATION GATES Irrigation gates include gates in irrigation canals and at inlets and outlets of water basins that feed (occasionally also drain) these canals. These water basins can be natural, man-made or combining the features of both.

30

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

FIG. 2.13 Automated irrigation gates developed by the ITRC, CA, USA.

Irrigation basins, canals and their gates originate from agricultural demand for water. As such, their purpose was originally to supply or drain only fresh water; never salt or brackish water. This changed when men began to discover the benefits of irrigation for other than agriculture activities. Such activities included sewage discharge, supply of drinking water, mining, various industrial needs and even the defense against enemy intrusion. An activity that gains significance in the recent decades is preservation of natural habitats—and in a growing number of cases the restoration of those habitats. The canals and gates utilized for this purpose control flows not only in fresh water but also in salt and brackish water. Examples of this are given in Section 3.17.4. In some cases, the interests of agriculture and of the natural environment can be opposite. An example is the fish migration that may be hampered by irrigation gates. Also, this issue is addressed in appropriate chapters of this book. Nearly all types of hydraulic gates are also represented in the field of irrigation. Several of them have been shown and shortly discussed in Section 3.17.4. Fig. 2.13 presents an example with one manually operated and two automated gates developed at the Irrigation Training and Research Center (ITRC) of the California Polytechnic State University, USA. The fruit trees in the background of this photo make the purpose of the gates very clear. As indicated in Table 2.2, the following features usually characterize the operation of irrigation gates: • Regarding opening and closing: partly, relatively frequently, controlled automatically, remotely or manually, fast (a few minutes or shorter), no watertight closing, normally under flow. • Regarding carrying hydraulic load: loads usually low and frequent, analyzed as quasi-static, 20–30 years of service life, load nearly constant and usually (not always) from one side. Most of these features are self-evident. Below are a few additional comments. Partial opening and the relatively frequent operation are inherent to the basic purpose of these gates. Flow regulation can only be performed in a partially open position, while an effective response to the varying hydrological conditions results in relatively frequent height adjustments. Automatic or remote control is more and more a requirement due to scattered locations and high commuter and labor costs. Fast movements result from small sizes and relatively small position adjustments, rather than from the need of quick response to the hydrological conditions. No watertight closing and operation under flow require little comment. Note however that irrigation gates can be vulnerable to debris carried by the flow. Depending on local conditions, various types of nets and grids need, therefore, to be used to prevent the obstruction of the gate. This can vary from light nets in open areas, like in Fig. 2.13, to quite heavy grid structures in forests, like in Fig. 2.14, or other areas of much debris. The photo in Fig. 2.14 leaves no doubt that heavy debris grids are very much desired in such areas. The hydraulic loads of irrigation gates are low in the sense that the skin plates of the gates themselves have relatively small areas and low heights. The differential water heads carried by those plates are usually also small. Exceptions from this rule can be found in regions where paddy-field farming is practiced, or in coastal areas where irrigation gates also combine the function of tide flow control. The frequency of hydraulic load variations on irrigation gates depends very much on the local hydrological conditions and often also on the season. Like in the operation profiles of most other gates, the character of hydraulic loads is considered quasi-static in the design. Fatigue and other dynamic aspects are usually irrelevant due to both low loads and low numbers and ranges of load variations. The service life of 20–30 years is a rough indication that usually reflects the economic optimum for steel structures of this size. Depending on local conditions, it can also be chosen differently if desired.

2.9 TEMPORARY AND MAINTENANCE CLOSURES

FIG. 2.14

31

Debris grid on an irrigation gate in Auvergne, France.

A special consideration is that the flow regulating gates in irrigation and wastewater systems are often subjected to more corrosive environments. This results from the use of fertilizers in agriculture and from various chemical and biological processes utilized in wastewater treatment. An example is the high concentration of nitrogen in the irrigation systems of sugar cane fields in Cuba, Puerto Rico and some southern regions of the United States. This issue and the appropriate measures for corrosion protection are discussed in more detail in Chapter 13.

2.9 TEMPORARY AND MAINTENANCE CLOSURES The group of temporary and maintenance closures covers mainly the gates that have been classified in Table 2.2 as “Emergency and service closures.” The reason of other choice of words is to point out that the gates of this group can serve a large number of purposes that are difficult to sum up under one short title. The main common feature of these structures is that they are used irregularly and for short periods of time. Here is a shortlist of purposes and arrangements that generate such a use: • New construction in hydraulic projects: Such projects may utilize bulkheads for multiple draining and filling of an area where hydraulic structure or a part of it is being constructed. • Temporary dry docks for prefabrication of floatable subassemblies: These are large foundations, piers, box sections of bridges and the like. Typical example is the prefabrication of tunnel sections that can be closed at both ends and floated to the construction yard. • Major maintenance or repair of existing gated closures: This can comprise crest or sill repair, exchange of gate tracks and guides, adaptation for another type of gate and many other works. In navigation locks, temporary bulkheads, or other closures can be installed facilitating the entire dewatering of the lock structure. • Regular or emergency exchange of the gate: Gates need to be exchanged for major maintenance, at the end of their service life or for repair after ship collision or other accident. Preferable way is usually to do it in the dry, which requires the use of temporary closures. • Emergency closures to isolate accidental contamination: Risks of accidental contamination exist in chemical and other industrial plants that utilize hazardous liquids. This also includes nuclear power plants with water-cooled reactors. Emergency closures reduce such risks. • Temporary floodwall systems: Floodwalls can be permanent, like in photo (a) of Fig. 2.15 or temporary, like in photo (b) of the same figure. The latter are only installed for the passage of floodwater and can be classified as temporary hydraulic closures.

32

2. OPERATION PROFILES OF HYDRAULIC CLOSURES

FIG. 2.15 Permanent and temporary floodwalls: (a) permanent floodwalls in New Orleans, USA, Hurricane Gustav 2008; and (b) temporary floodwalls along the Danube, Austria, flood 2013 (a) Photo USACE New Orleans District; (b) Photo Robert Zinterhof.

FIG. 2.16 Gates in upstream crown of Lock 7 in the Welland Canal, Canada: (a) sector gate for collision protection and (b) miter gate for locking.

One can see that temporary and maintenance closures are utilized in a large number of applications of different character and different requirements. Despite this diversity, there are many common features that characterize the operation of such closures. These features have been indicated as follows in Table 2.2: • Regarding opening and closing: entirely, seldom, to erect and disassemble manually using hired equipment, very slow (1 h or longer), often watertight, no adjustments or motion under flow. • Regarding carrying hydraulic load: high but relatively seldom, predominately quasi-static, 5–30 years of service, load variable or constant depending on application, always at one side. Most of these features are self-evident. Below are a few additional comments: Once erected, the structures of this group are usually not moved or adjusted until there is no purpose for their further use and they can be disassembled. This and the seldom use justify the predominately manual installation and disassembly of these closures. The equipment used for these handlings can, obviously, include a mobile crane or other devices, but it is often hired for this purpose and makes no part of the site permanent hardware.

2.10 OTHER HYDRAULIC GATE APPLICATIONS

33

The watertight closing is desired for some applications, like bulkheads or maintenance closures, but not necessarily for the other, like some emergency closures or floodwalls. There is no common line regarding this feature. Hydraulic loads of temporary and maintenance closures are high and can have variable components, but the seldom use of these closures makes it usually unnecessary to consider dynamic risks like fatigue. A quasi-static load definition is normally sufficient. The design load model is then similar to the one presented as example for a lock gate in Fig. 2.4. The service life of 5–30 years represents a rough indication also for this group of gates. Like in the case of irrigation gates, it usually reflects the economic optimum for steel structures of similar sizes. The lower limit of 5 years may surprise but it is meant to cover the views that some closures of this group can be designed as disposable. This applies, for example, to emergency closures in process industry, nuclear power plants or the gates with a main task of dissipating the energy of ship collision. These structures will statistically operate much longer, because such emergencies happen very seldom, but they will be scrapped after their first operation. A special case of the latter is the vertically hinged sector gate that operates in the Welland Canal in Canada. That canal with its eight locks offers a navigation passage between Lake Erie and Lake Ontario, parallel to the Niagara River. The sector gate, shown in photo (a) of Fig. 2.16 is installed on the upstream side of Lock 7. The function of this gate is not to hold a differential water head. That task is performed by miter gates of Lock 7, Fig. 2.16b. However, as the distance to the upstream Lock 8 is large (about 25 km), there is a risk of a ship not limiting her speed in a timely manner and colliding with the miter gate of Lock 7. Closing the sector gate protects then the miter gate and enables the dissipation of collision energy. Considering the size of vessels passing the Welland Canal (see photo) and the large differential water head at Lock 7 (14.0 m), this precaution is not exaggerated.

2.10 OTHER HYDRAULIC GATE APPLICATIONS The eight operation profiles of hydraulic gates described do not exhaust all application possibilities of such gates. As mentioned in Section 2.1, other application fields include, for example, sewage processing plants, cooling systems of nuclear reactors, closures in ship lifts, submerged sites of various kinds, liquid processing industrial plants, water recreation and sport facilities etc. It is also not necessarily water that gates and valves are used to handle; an introduction to the mechanics of a wider range of fluids has in this view been given in Ref. [9]. These application fields are not discussed separately due to their relatively narrow size. The gates that operate in such fields will also receive less attention in the following chapters. The character of their operation may, however, resemble one or more application fields that have been discussed above. The reader is, therefore, encouraged to seek analogies and similarities in such cases; and to use the guidance that has been presented for the gates in other fields.

References [1] J.O. Grady, System Requirements Analysis, Elsevier Academic Press publications, Burlington (MA), 2010. [2] Rijkswaterstaat, ProRail, et al., Leidraad voor Systems Engineering binnen de GWW-sector, version 3, The Hague, https://www.leidraadse.nl/ assets/files/downloads/LeidraadSE/V3/Leidraad_V3_SE_web.pdf, 2013. [3] Rijkswaterstaat, Leidraad RAMS, Sturen op prestaties van systemen, The Hague, https://www.leidraadse.nl/assets/files/downloads/Publicaties/ leidraad_rams_sturen_op_prestaties_van_systemen.pdf, 2010. [4] R.A. Daniel, O rozbudowie zespołu portowego Amsterdam Seaports. Inzynieria Morska i Geotechnika, Gda nsk, 2012. No. 3/2012. [5] P.A. Kolkman, Development of vibration-free gate design, IAHR/IUTAM Karlsruhe Symposium “Practical Experiences With Flow-Induced Vibrations” 1979, Springer Verlag, Berlin, 1980. [6] L. Hao, et al., Urbanization dramatically altered the water balances of paddy field dominated basin in southern China, Hydrol. Earth Syst. Sci. 19 (7) (2015). http://www.hydrol-earth-syst-sci.net/19/3319/2015/hess-19-3319-2015.pdf. [7] R.A. Daniel, J.S. Leendertz, Geïntegreerd ontwerp van de hefschuiven Hartelkering, Civiele Techniek, Gorinchem, 1994. No. 4. [8] USBR: Hoover Dam Appurtenant Works, Drawing No. 45-D-3230, 1-25-36, Retraced 8-10-48, Rev. 6-1-56, US Bureau of Reclamation. [9] D. Pnueli, C. Gutfinger, Fluid Mechanics, Cambridge University Press, Cambridge (UK), 1992.