OLABISI ONABANJO UNIVERSITY

College Of Engineering and Environmental Engineering

Faculty of Engineering
Department of Civil Engineering 2023/2024 Rain Semester
Examination
Course Title: Water Resources Engineering
Course Code: CEG 502
Time Allowed: 2hrs Unit: 3
Units
Instruction: Answer questions 1 & 2 any other 2 questions

1. Determine the forces due to self-weight, water pressure and uplift pressure of the gravity dam
shown in Figure 1, considering the weight of the dam, water pressure, and uplift pressure.
Assume weight of concrete (Wc) =24KN/m3, Weight of water (Ww) = 9.81KN/m3. (20mks).

Figure 1

2. Perform the flood routing for a reach of river given x = 0.15 and k = 2.3 days. The inflow hydrograph
using t = 1 day is shown in the table below. Assume equal inflow and outflow rate on the 16th. From the
inflow hydrograph given, calculate the outflow rate on the 26th using Muskingum method.(20mks)
Date Inflow CoI2 C1I1 C2O1 Comp. outflow
16 4260 - - - 4260
17 7646 482 1466 2762 4710
18 11,167 705 2632 2792 6129
19 16,730
20 21590
21 20,950
22 26,570
23 46,000
24 59,960
25 57,740
 26 47,890
27 34,460
28 21,660

3(a). Write short notes on the three (3) types of water intakes. (6mks)
(b). List four (4) factors to be considered in water intake design. (4mks)
(c). Write short notes on the following terms as used in navigation: lock, chamber, gates, guide
walls, guard walls, transit time (5mks)

4(a). Enumerate six (6) factors to be considered in selecting the site for a dam. (6mks)
(b). List five (5) provisions used to secure the earth dam against failure (5mks)
(c). Explain four (4) classification of dams based on function performed (4mks)

5(a).What is a water intake and state its two functions. (3mks)

(b).Write short notes on navigation locks and channels (4mks)
(c). Description of the typical steps (4) involved in the operation of a navigation lock (8mks)

6(a). What are water control works (2mks)

(b). Write short notes on the following (i) levees and floodwalls (ii) weirs and barrages (iii)
aqueducts and canals (6mks)
(c). List 4 features of a spillway (4mks)
(d) State three functions of "gates, valves, and regulators" (3mks)
Q1
 Q2
Perform the flood routing for a reach of river given x = 0.15 and k = 2.3 days. The inflow
hydrograph using t = 1 day is shown in the table below. Assume equal inflow and outflow rate
on the 16th. From the inflow hydrograph given, calculate the outflow rate on the 26th.

O2 = C0I2 + C1I1 + C2O1

where:
C0 = (-k x +0.5t)/( k – k x + 0.5t) = 0.0631
C1 = (k x + 0.5t)/ (k – k x + 0.5t) = 0.3442
C2 =( k – k x – 0.5t)/ (k – k x + 0.5t) = 0.5927

Date Inflow CoI2 C1I1 C2O1 Comp.

outflow
16 4260 - - - 4260
17 7646 482 1466 2762 4710
18 11167 705 2632 2792 6129
19 16730 1056 3844 3633 8533
20 20950 1322 5758 5058 12138
21 26570 1677 7211 7194 16082
22 46000 2903 9145 9532 21580
23 59960 3783 15833 12790 32406
24 57740 3643 20638 19207 43488
25 34460 2174 19874 25775 47823
26 21660 1367 11861 28345 41573
27 34680 2188 7455 24640 34283
28 45180 2851 11937 20320 35105
 Q3.

Direct Intake: These are located waters, and cheaper than any other intake. Direct intake is
suitable when the source is deep such as rivers or lakes, and also when the embankment is
resistant to erosion and sedimentation (very stable)
Canal Intake: These are built and used to draw water from canals. A masonry chamber with an
opening is built partially in the canal bank. The opening is provided with a course screen. From
the chamber water is drawn by a pipe having a bell mouth covered with a perforated
hemispherical cover.
Reservoir Intake: The intake tower is either located at the spillway section or at the toe of an
earthen dam. The foundation of the tower is separated from that of the dam. It is constructed on
the upstream side. A number of inlets at various levels are provided by the tower to compensate
for water level fluctuations. When reservoirs are at such a level that water can flow by gravity to
the purification works, then an intake tower is not required.

Factors to be considered in the location of an intake:

a) Intakes should be located where there is no fast current which may damage the intake causing
interruption in the water supply.
b) The ground near an intake should be stable. A straight section of the river is preferable as
erosion is minimal.
c) The approach to the intake should be free from obstacles.
d) The intake should be well below the water surface and well above the bottom of the water
body for preventing floating matter and suspended matter near the bottom respectively.
e) The intake should be located at some distance from the bunk to avoid contamination of bark.
f) The intake should be located on the upstream of the town.

Write short notes on the following terms as used in navigation and locks: lock chamber,
gates, guide walls, guard walls, transit time

a. Lock chamber. A lock chamber refers to the portion of the structure encompassed by the lock
walls and the gates at each end.
b. Gates. A movable barrier or barriers at each end of a lock chamber that can be opened or
closed to permit a vessel to enter or exit from a lock chamber. When the gates are closed, they
must be capable of withstanding the hydraulic pressure caused by the differences in water levels
upstream and downstream from the lock.
c. Guide walls. Guide walls are walls that extend outward from each end of the lock chamber
which serve as guide structures to aid vessels or tows in aligning for entry into the lock. For
barge locks in the United States, guide walls are usually a prolongation of one of the lock
chamber walls.
d. Guard walls. Guard walls are placed at each end of a lock opposite to the guide walls. The
guard walls are aligned to provide flared entrances to the lock and as the name implies provide a
barrier to guard a tow from unintentionally entering areas where hazardous currents exist.
e. Transit time. Transit time is the total time required for a tow to move into a lock from a
waiting point (arrival point), be raised or lowered, and then proceed out of the lock to a position
where it will cause no interference to any other tow that needs to transit the lock.
 Q4

Factors to be considered in site selection include (6mks)

Topography- a narrow gouge in the river reach that opens out to a large area upstream is
preferable.
Foundation- this should be us firm as possible
Suitable materials for construction should be available at or the site
The reservoir should be water high
The reservoir should be cup-shape preferably with a flat bottom but steep slopes.
The cost of diverting the stream,
Availability of labour, and
Traffic requirements on top of the dam.

List five (5) provisions used to secure the earth dam against failure (5mks)
Provide the rip rap to protect the upstream face against water wave, erosion, and during sudden
drawdowns
Turfing protects the downstream face against erosion by rain or winds.
Internal drain prevents seepage through the dam to the downstream face of the dam. This results
in piping through the dam or the foundation.
The toe drain prevents seepage that may also cause piping and erosion of downstream toe due to
tail water
The central core is impervious and controls seepage through the dam, the transition filter also
prevents seepage to an extent in that the particle sizes are still smaller than that of the upstream
shell but not as small as that of the core materials. In this way piping is also prevented.
The pervious upstream shell provides free drainage during sudden draw down thus providing
stability.
The pervious downstream shell provides a drain to control the phreatic lie. The phreatic line is
brought very how such that failure or piping does not occur.

Explain four (4) classification of dams based on function performed (4mks)

Storage dams for impounding water for developmental uses. They can be used to store water
during rainy season, when the river stage is high. The stored water is used during the dry periods
for irrigation, water supply and hydropower.
Diversion dams for diverting stream flow into canals or other conveyance system i.e. they are
constructed to divert river water to another location where it is needed.
Detention dams to hold the water temporary to retard flood flows i.e. they are used for flood
control. During the high floods, such dams detain the water upstream and release it down stream
in quantities that will not cause any damage.
Coffer dams - used in construction along waterways. They are constructed to keep water away
from the construction site so that construction can be done on the dry place. The dammed water
is diverted away from the site using a diversion tunnel.
 Q5
a.A water intake is a structure required to withdraw water from a river, lake or reservoir. The
primary functions of an intakes is to:
To supply highest quantity of water from the sources
To protect piping and pumps from damage or clogging as a result of floating and submerged
debris. (3mks)
b. Navigation Locks: A navigation lock is a structure that enables vessels to transit through
sections of a waterway with different water levels. It consists of a chamber enclosed by gates at
both ends, allowing water levels within the chamber to be raised or lowered to match the water
levels on either side of the lock. Locks help maintain a consistent water depth, overcome changes
in elevation, and provide a controlled passage for ships, boats, and barges.
Navigation channels are artificially created or modified waterways designed to provide a clear
and navigable path for vessels. They are usually dredged or excavated to remove obstacles, such
as sandbars, rocks, or shallow areas, ensuring sufficient water depth for safe passage. Navigation
channels may also include markers, buoys, and other aids to guide mariners along the desired
route. (4mks)
c. Description of the typical steps (4) involved in the operation of a navigation lock
i. Approach Channel: A ship enters the approach channel, which leads to the entrance of the
lock. The approach channel is often wider and deeper than the lock itself to accommodate the
vessel's maneuvering and provide ample space for other vessels waiting to enter or exit the
lock.
ii. Entrance Gates: At the entrance of the lock, there are gates that can be opened and closed to
control the flow of water and prevent water leakage. These gates are usually massive and
sturdy to withstand the pressure of the water.
iii. Lock Chamber: The lock chamber is a confined space where the vessel is placed. It is a
rectangular or cylindrical structure with sufficient length, width, and depth to accommodate
vessels of various sizes. The chamber is filled or emptied with water to match the water level
of the section of the waterway the vessel is entering or leaving.
iv. Control Mechanisms: Locks are equipped with control mechanisms, including valves, pumps,
and gates, to regulate the water flow in and out of the chamber. These mechanisms allow the
water level inside the chamber to be raised or lowered to match the desired level.
v. Exit Gates: Once the water level inside the lock chamber matches the desired level, the exit
gates are opened, allowing the vessel to exit the lock and continue its journey at the new water
level. (8mks)
 Q6

(a).What are water control works: Water control works are engineering structures and systems
designed to manage, control, and utilize water resources efficiently and sustainably. These
structures are critical for flood control, irrigation, water supply, and environmental conservation.
This lecture will cover the types, design principles, and applications of various water control
works (2mks)
(b). List 4 features of a spillway (4mks)
Have adequate discharge capacity
Must be hydraulically and structurally safe
Have an erosion-resistant surface
Have an energy-dissipating device with it
Have a discharge that does not exceed the safe discharge capacity of the downstream channel
Not have discharges that will cause damage to the toe of the dam or downstream.

(c).State three functions of "gates, valves, and regulators" (3mks)

A gate is a closure device in which a leaf or closure member moves across the water passage
from an external position to the water passage to control the water flow.
A valve is a closure device in which the closure member is fixed with respect to the water
passage and is either rotated or moved longitudinally to control the water flow.
Regulators are gates and valves that serve as regulating devices that operate under full pressure
and different flow conditions.

(d). Write short notes on the following (i) levees and floodwalls (ii) weirs and barrages (iii)
aqueducts and canals (6mks)
Levees and Floodwalls are used to protect land from flooding by containing or diverting
floodwaters. Levees are earthen embankments constructed along rivers while floodwalls are
concrete or masonry walls built to higher specifications than levees, often used in urban areas.
Weirs and Barrage: A weir is a raised concrete crest wall constructed across a river in a
diversion head works. A weir consists of most of the raised concrete wall and a small shutter at
the top. A barrage serves the function of a weir as well. However, it has a low concrete crest wall
with high shutter gates. Thus, it allows for better control of the river flow (as a result of the high
gate) as compared with a weir.
Aqueducts and Canals are used to transport water over long distances for irrigation, industrial,
and municipal use. Aqueducts are structures built on a canal where it crosses natural drainage
(e.g. rivers, streams). Aqueducts are concrete structures built to carry the discharge of the canal
They are placed at the section where the canal crosses a stream or river. Canals are used for
diversion works and these take water away from the storage created by a weir or barrage. Canals
could sometimes run across a drainages channel or road works. Though this should be avoided as
much as possible. It is sometimes inevitable. While the canals serve as concrete structures to
carry diverted water from diversion works, Where the canal passes over the stream or river
channel, it is simply referred to as an ordinary aqueduct. Where the canal passes below the
river/stream it is referred to as a syphon or a canal syphon.