Water Resources Engineering I

1. CVS 445: Water Resources Engineering I
Department of Civil & Structural Engineering
Moi University
Lawrence Omai
E-mail: lawrenceomai@gmail.com

2. Course Outline
1. Introduction to WRE
2. Integrated Water Resources Management and development
(IWRM/D)
Definition
Importance
Process of implementation
Water management (Dublin) principles
Water users
Implication of change
3. Water interaction and balance
4. Catchments based planning /management
5. Legal & institutional framework and international obligation for
IWRM
Kenya in focus, Water ACT 2002

3. Course Outline
• Fieldwork: study an integrated water resources project.
• Laboratory: assessment of the sodium adsorption ratio and
conductivity measurements.
Reference
1. Andrew A. Dzurik (2003, Ed.), Water Resources Planning , Rowwman
Publishers, UK.
2. Linsley, Ray K. eta-al, (1992, 4th Ed.), Water Resources Engineering,
McGraw-Hill.
3. Integrated Water Resources Management Plans Training manual and
Operational Guide March 2005

4. Water Resources Engineering involves/has roots in:
• Supply of water for human use
• Removing water when humans are finished using it.
• Developing methods of avoiding damage from excess water
(floods).
 Major work of WR-Eng. is Planning and mgt of constructed
facilities that address these tasks.
• The dvpt of water resources requires the conception, planning,
design, construction, and operation of facilities to control and
utilize water.
• It is basically a function of civil engineers
Introduction to WRE

5. Introduction to WRE cont’d…
 Water resource problems are also the concerns of
environmentalists, economists, political scientist, geologists,
electrical and mechanical engineers, chemists, biologists and
other specialists in the natural and social sciences.
 Career opportunities undergraduates & Graduates can be
found in consulting firms and in government entities charged
with supplying water or dealing with its hazards.

6. Fields of water Resources
• Control of Water: to avert property damage e.g. highway
culvert design, flood mitigation, sewerage, land drainage etc.
• Utilization of Water: beneficial use e.g. Water supply, irrigation,
hydro-electric power development, and navigation
improvement.
• Water Quality Management: Pollution threatens the utility of
water for municipal and irrigation.

7. • Little skill is required to design a structure for some purpose if
unlimited funds are available.
• The special ability of the engineer is reflected in the planning of
projects which serve their intended purpose at a cost
commensurate with the benefits.
• COST-Benefit Analysis necessary
• Should be demonstrated that Cp<<Bexp to warrant the required
investment.
• Engineers plan for the uncertain future without know how
whether the loads used to design structures cannot be
exceeded.
• Generous factors of safety are used to lower the probability of
failure which may increase the cost of the project.
• To have a compromise between safety and economy, the
Economics in water resources

8. For example, the occurrence of a flood with probability p in N years can be
estimated as follows:
1. If the probability of occurrence is, p,
2. Then probability of not occurring is = (1 – p)
3. Probability of not occurring in 2 years is = (1 – p) (1 – p) = (1 –
p) 2
4. Probability of not occurring in n years = (1 – p) n
For N = n;
5. Probability of occurring once in N years is = 1 - (1 – p) N
Economics in water resources cont’d….

9. • Two main sources of water:
 Surface Water
 Ground Water
• Their quantity and quality are influenced by geography, climate,
and human activities
• Ground water can normally be used with little or no treatment.
• Surface water, on the other hand, often needs extensive
treatment, particularly if it is polluted.
• Where there is lack of ground water or surface water may make
the desalination of seawater and reclamation of treated waste
water necessary. Though costly, but water of adequate quality for
Sources of water

10. Surface water
• Rivers and lakes are important sources of public water supplies
because of high withdrawal rates they can normally sustain.
• Surface waters are open to pollution of all kinds.
• Contaminants arise from industrial and municipal wastes, run
off from urban and agricultural areas, and soil erosion at river
catchments.
Storage of surface water
• A water supply, irrigation, or hydroelectric power project
drawing water directly from a stream may be unable to satisfy
the demands of its consumers during low flows.
• Hence necessity of dam construction

11. Surface water storage

12. Surface water storage cont’d…
1. The normal pool level: is the maximum elevation to which the
reservoir surface will rise during ordinary operating conditions.
• For most reservoirs normal pool is determined by the elevation of the spillwa
crest or the top of the spillway gates.
2. Minimum pool level: is the lowest elevation to which the pool is to
be drawn during normal operating conditions.
3. Useful storage: The storage volume between the minimum and
the normal pool levels.
4. Dead storage: The water below minimum pool level.
5. Surcharge storage: discharge over & above the spillway,
experienced during flooding.

13. Determining capacity of a reservoir
1. Formulae for volumes of solids: Can be used for reservoirs of
regular shape.
2. Capacities of reservoirs on natural sites must usually be
determined from topographic surveys.
 An area elevation curve is constructed by planimetering the
area enclosed within each contour within the reservoir site.
 The integral of area-elevation curve is the elevation storage,
or capacity curve for the reservoir.

14. Reservoir Sedimentation
• The storage volume of a reservoir is affected by
sedimentation.
• If the sediment inflow is large compared with the reservoir
capacity, the useful life of the reservoir may be very short.
• The useful life is terminated when the Q occupied by sediment
is sufficient to prevent the reservoir from serving its intended
purpose.
• Hence soil erosion control necessary at the watershed scale.
• Rate of erosion is the rate at which erosion occurs and
measures how much sediments are removed at a given time
• The ratio of sediment yield of a drainage basin to the total
amount of sediment moved by sheet erosion is the sediment
delivery ratio.
– It is the sediment measured at a specific point over a specific time in a
stream. It gives information on how a stream carries sediments from the

15. Reservoir Sedimentation cont’d…
Ways of Addressing Sedimentation Problem
1. Designating a portion of the reservoir capacity as sediment
storage.
• This is a negative approach as it only postpones the problem.
2. Selecting a point along the river where sediment inflow is very
low.
• Some basins are more prolific sources of sediment due to soil type,
land slopes, vegetation cover, land use and rainfall characteristics.
3. Soil conservation methods.
4. Provision of sluice gates; discharge of finer sediments.

16. Streamflow Measurement
• Necessary for water resource assessment studies and
hydrologic balance studies.
• 2 broad categories of stream measurement are:
– velocity area method and
– dilution gauging.
co = background concentration of the flow designated by q
C1 = known concentration of tracer added to the stream at the rate q1
C2 = sustained final concentrations of the mixed flow with the rate q+q1
Then
qco + q1c1 = (q + q1) c2, can be solved to yield
The above derivation is based on the premise that the concentration c2 has
stabilised in the stream flow.
1
2
2
1
q
c
c
c
c
q
o












17. Groundwater
• Unlike other resources of the earth GW can be replenished.
• Difficult to explore and harness because it is invisible.
• Not as susceptible to pollution as surface water, but once
polluted, its restoration, if even possible, is difficult and long
term.
• Most pathogenic organisms and many undesirable substances
are removed by filtering action of soil particles.
• The availability of GW from an aquifer at a place depends on
the rates of withdrawal and replenishment (recharge).

18. Assignment #01
Briefly discuss the role of a water resources
Engineer in the following sectors
• Water Supply and Sanitation
• Irrigation and Drainage
• Energy
• Environment