physical design and planning of barrage .

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Physical Design and Planning Of Barrage
Introduction
A barrage is a structure constructed across a river and includes diversion structures that lead to raising the level of water in a river and control of its flow. For the efficient functionality of a barrier (Albinson 13), it has to have components such as;
Canal head regulator that assists in the regulation of inflow of water into the canal
Devices that enable for sediment exclusion that helps in sediment removal that is in suspension from river water. Likewise, these devices also support in the inhibition of entry of sediments in the canal
Stoplogs and Gates in flow management that takes place in the major structure for diversion and the head regulator. Normally, stop logs are used in emergency situations that involve the closure of the inflow taking place in barrage’s bay or the head regulator
Training operations that occur on rivers and essential in guiding of water towards the barrage
Facilities for fish passage and navigation that ensure there is no obstruction on the river brought by the barrage construction so that ships, boats, and fish may move freely in the river.
Regarding the above components, the chief part in the design of a barrage is the design of head regulator. However, the paper will also evaluate on the devices that facilitate the removal of sediments that ever lie in suspension.
Design
As already mentioned earlier, regulator present in the canal’s of head taking and also exist within the barrages backward is the canal head regulator.

The structure assists in the regulation of water supply into the canal for purposes such as irrigation, HEP production, domestic or industrial water supply and many others (Albinson 25). Also, this component assists in the regulation of silt entering into the canal. For this reason, the design of this structure must take into consideration of the hydraulic and structural performances.
Layout plan and location
Canal head regulator’s position has linkages with work diversion’s position. Due to this reason, it is essential to have the position of the head (Albinson 36) regulator close to the diversion structure as much as possible especially next to the end of the outer curve.

Figure 1: The position of a canal head regulator on a barrage
Despite the head regulators take place near the abutment of structure for diversion being appropriate, to some extent, it is not possible to it at the same position due effects of topography brought by hills and much more. In such situations, the situation of the head regulator may be at the upstream close to the periphery of the pond while not at the very distance from the prime structure (Albinson 45). Where there are small requirements of discharge, there may be the need to provide head regulators based on opening situated at the abutment’s wing. In this case, there is a need to properly align the head regulator about the axis of the barrage with the aim of ensuring a reduction in the silt quantities finding their way into the canal plus also for the purpose of avoiding backflow as well as the formation of stagnant zones within the pocket. To realize this, the regulator’s axis needs to be kept at an angle that varies from 900 to 1100 as depicted in the below figure 2

Figure 2: The inclination of a regulator and the axes of a barrage
Though this angle is almost recommendable, some checks are still necessary on the final layout on that particular model used in the assessment several combinations of the under slice gates and the gates of the canal regulators (Albinson 59). A layout of a typical canal regulator is as shown in the below figure 3. Meanwhile, the longitudinal section within a structure is as presented in figure 4and another one off taking through sideways a sediment excluder, is also as shown in figure 5.

Figure 3: A canal head regulator typical layout

Figure 4: Canal head regulator’s sectional view

Figure 5: Canal head regulator, section with the inclusion of excluder
A head regulator’s construction may occur on an independent basis from the abutment that is free from it by making use of the desired joints and seals. On the same note, its construction may involve the use of monolithic that is associated with it (Burt and Andrew 47). The abutment of the regulator may be the set fee from the floor that belongs to it by following the longitudinal joints and seals. On the same note, their constructions may also be monolithic through the application of raft floor within the head regulator. At last, the whole structure’s design may finally be in the shape of trough as shown in the below figure 6

Figure 6: Monolithic Trough section of a head regulator
Water regulation within the head regulator is facilitated by the vertical lift gates. However, presently, the radial gates are emerging to be common as much as their preferences are in headworks that have relatively big variations in the elevation of the levels of pond and supply level of the canal that would not allow for submergence of the trunnion pin of the radial gate (Burt and Andrew 54). Often, a road bridge is factored across the head regulator in cases of vehicular traffics or instances of inspection. In such situations, it would be possible to have the connection of them with road and bridge about the major barrage structure. Due to this reason, the gate operations need to have a working platform within the regulator’s head.
Hydraulic design
The design components of a hydraulic design of a canal head regulator are as stated below;
Fixing of the level of pond of the pool that is at the backward of the barrage
Fixing of the level of crest and sill’s shape and width
Fixing of waterway, quantity and width spans and gate opening heights, breast wall requirements and much more
Approaches to shape and components
The structure’s safety due to sub-surface conditions of flow
Arrangements for dissipation of energy
Pond level
The level of pond in the under sluice pocket upstream of the canal head regulator may be got through the addition of the working head that penetrates through the canal design‘s discharge via the regulator and the level of water in the canal at full levels of supply as well as the head losses that take place in the regulator. In some situations, there may be restrictions on the level of a pond and this case the complete supply level needs fixation through subtraction from the working head of the level of the pond.
Crest level, width, and shape of sill
Often, there is an interrelation between the sill crest level and waterway. The level of sill needs to be fixed through subtraction from the level of the pond and the sill’s head that is required for passage of complete supply discharge in the canal at an identified pond level. To establish the control on sill’s entry into the canal, it is appropriate that sill available at the regulator’s head be maintained at higher when compared to the sill available below the sluices (Burt and Andrew 67). The difference, in this case, may be between 1.2 to 1.5 meters. Where there is the provision of silt excluders, then the level of crest needs to be kept close to 0.5 meters higher when compared the surface top of the silt excluders. The over sill required, H essential for the passage of discharge Q through an active waterway L may be established from the below (Burt and Andrew 78) relationship;
Q = Cd LeHe3/2 (1)
Where Q represents discharge that occurs in m3/s
Cd is the co coefficient of discharge
Le defines the efficient waterway
He is equivalent to head over crest that passes discharge Q, in meters
The discharge coefficient Cd always is not constant due to factors such as;
Sill’s overhead
Width and shape of the sill, W
Upstream slope, Zu
Downstream slope, Zp
Sill’s height above the floor’s upstream, P
Surface roughness

Figure 7: the desired values for coefficient of discharge for varying He, P and W
Determination of Quantity and Width of Spans and Waterways
It is essential to have in place a recommendable waterway that can allow for passage of discharge needed in the head regulator with any problems arising out of it (Burt and Andrew 83). Upon making decision on the effective way, the total energy that exists between the abutments plus also the inclusion of the piers need to established based on the below equation;
Lt = Le + 2(N Kp + Ka) He +W (3)
Where
Lt = total waterway
Le = an effective waterway
N = total piers
Kp = contraction coefficient of pier
Ka = t contraction coefficient of abutment
He = head over crest
W = piers’ total width

Figure 8: Values recommended for Ka and Kp
Shape and other components considerations or approaches
There is the need to provide the upstream inlet with circular, hyperbolic or elliptical transitions. In this case, the splay may be in the category of 1:1 or 3:1. On the other hand, at the downstream sections, a straight, hyperbolic or parabolic transitions (France 59) may also be factored in together with splays that have a range of values of 3:1 to 5:1 as shown in the below figure 9. Dimensions must put be to test for model studies so as to reach the final estimates. Likewise, the wing walls need to be kept vertically upwards till to the conclusion of the impervious floor above which they need flaring from the vertical and exact slope of the section of the canal.

Figure 9: Upstream inlet transitions
Arrangements for surface flow conditions for the structures and energy dissipation
For the cases of head regulators situated on the foundations that are noncohesive and erodible, the portion that is unlined on the floor must have protection against scour. However, for a scenario where the situation of a head regulator is on the nonerodible beds, the said precautions may not hold (France 68). On the other hand, for the situation of the upstream edge of the floor of a regulator, it calls for the cutoff or even the sheet pile to be present.

Figure 11: An upstream head of regulator’s flow sheet pile
Concerning the downstream of sill’s side, the head regulator must have efficient dissipation of energy plans that is often achieved through the formation of the hydraulic jump from various conditions of discharge. Likewise, for gate openings that have the pond level at the upstream, the discharge that takes place in the head regulator must be established. From the values obtained here, levels and lengths of cistern will be determined and the reigning values taken in consideration for the profile (Ndubisi 64). Devices that dissipate extra energy such as chute blocks, end sill, friction blocks may also factor in where applicable. In the case of head regulators that have small capacities of discharge, devices that dissipate extra energy except end sill may not be appropriate.
For thickness evaluation of the head regulator’s floor, the profiles of the hydraulic jump for various conditions of flow must be plotted. There is always a variation in the flow conditions for many discharges taking place in the canal about the gate opening the instance of the regulator (Ndubisi 72). In this regard, then, there is need to establish on the average jump trough’s height through the deduction of the jump profile levels from the associated line of hydraulic gradient. The line, in this case, will be the balanced head where the floor’s safety needs to be ensured.
Structure’s safety based on the condition of the surface flow
Like the main barrage’s design, the head of a regulator’s floor must be checked against cases of critical sub-surface flow conditions particularly when the head regulator is situated on a foundation that is permeable as shown in the below figure 11.

Figure 11: A head regulator’s critical surface floor that requires checking for canal gate closed based on condition.
A gradient of exit for the upward case of rising seepage flow at downstream of the solid apron must be established. On the same note, the exit gradient must be safe based on the kind of bed material. On the same note, there is the need to establish on the full length of the solid floor and the depth of the downstream cutoff about the conditions that get enumerated for subsurface flow destined for main barrage (France 76). Contrarily, there is the need to take into consideration that the floor’s total length may be decreased through the increment in the downstream cut off’s depth and vice-versa. A unique factor is that the increase in the cut-off down stream’s depth may lead to an increment in the uplift pressures’ concentrations especially the floor’s half downstream. For this reason, a balance between these two aspects needs to be reached for economization.
Conclusion
The aim of this paper was the explanation of how to design a barrage. On keen consideration of the concepts covered here, there is no reason why an individual should not end up with a successful barrage upon the implementation of the concepts explained. For those who hope to construct such kind of a structure, the concepts covered in this paper will indeed of great value to them.
Works Cited
Albinson, B. Fundamentals Of Smallholder Irrigation. 1st ed. Colombo, Sri Lanka: International Water Management Institute, 2002. Print.
Burt, Neville and Andrew Rees. Guidelines For The Assessment And Planning Of Estuarine Barrages. 1st ed. London: Thomas Telford, 2001. Print.
France, R. L. Handbook Of Water Sensitive Planning And Design. 1st ed. Boca Raton, Fla.: Lewis Publishers, 2002. Print.Ndubisi, Forster O. The Ecological Design And Planning Read. 1st ed. Washington, DC: Island Press/Center for Resource Economics, 2015. Print.