ENGINEERING

HYDROLOGY
CE-332
LECTURE 1-a
REFERENCE BOOKS

 Awan N. M, Surface Water Hydrology (Vol-1), National Book Foundation,

Islamabad Pakistan.
 Chow Ven Te, David R. Maidment, Larry W. Mays, Applied Hydrology, McGraw
Hill Book International Edition.
 Linsley Ray K, Kohler Max A, Joseph L.H Paulhus, Hydrology for Engineering
(3rd Edition).
 Maidment David R, Hand Book of Hydrology.
 Wilson E.M. Engineering Hydrology.
CONTENTS

 Introduction to Hydrology
 Hydrological Cycle
 Engineering Hydrology and its Domain
 Scope and Significance
 Hydrologic Equation and its Applications
INTRODUCTION TO HYDROLOGY

 Hydrology is the earth science. It encompasses the occurrence, distribution,

movement and properties of the waters of the earth and their environmental
relations. (Warren Weissman)

 Subject matter can be defined in two broad phases

 Hydrologic Data Collection
 Analysis and interpretation
HYDROLOGICAL CYCLE

 A continuous Process by which water is transported from the oceans to the

atmosphere to the land and back to the sea
 The driving force for the global water transport system is provided by sun
 Water quality also changes during the cycle

Precipitation
under proper
Evaporation conditions

Transport Distribution of
through air rain water in
masses several ways
HYDROLOGICAL CYCLE
ENGINEERING HYDROLOGY & ITS DOMAIN

 It includes those segments of the fields which are pertinent to planning,

design and operation of engineering projects for the control and use of water
 What flood flows can be expected over a spillway or highway culvert or in urban
storm drainage system ?
 What reservoir capacity is required for irrigation or municipal water supply during
droughts ?
 What effects will reservoirs, levees and other control works exert on flood flow in
stream ?
 What are reasonable boundaries for the floodplain ?
SCOPE & SIGNIFICANCE

 Water is the basic need for human life

 To cope with extreme hydrological conditions Floods and droughts
 Food habits of areas are governed by the hydrologic conditions
 Water resource management (Water available and water demand)
 Input data required for design of hydraulic structures
HYDROLOGICAL PROCESSES

 Precipitation
 Canopy interception
 Evaporation
 Transpiration
 Infiltration
 Depression storage
 Surface runoff
 Ground water flow
 Subsurface water flow
 River flow
HYDROLOGICAL PROCESSES

 Precipitation: A process in which the moisture reaches the surface of earth

from atmosphere. It is basic hydrological input. There are many forms of
precipitation e.g., rainfall, snow and many others to be discussed in coming
lectures
 Canopy interception: is the rainfall that is intercepted by the canopy of a
tree and successively evaporates from the leaves.
 Evaporation: transformation of water from the surface of earth to the
atmosphere. It is the reverse process of precipitation.
 Transpiration: Evaporation through plants. The water which is transpired is
below the surface of earth. Through roots, trunks, branches and leaves, the
soil water is Transpired to atmosphere.
 61% water of precipitation on land is RETURNED BACK into atmosphere by
evapo-transpiration
HYDROLOGICAL PROCESSES
 Infiltration: fraction of rain water penetrates into the ground is called
infiltrate and process is known as infiltration. Infiltration occurs from Land
cover which is permeable.
 Depression Storage: water filled in depression is called depression storage.
It depends on unevenness of the surface.
 Surface runoff: Rest of water that moves on the ground surface is called
surface runoff. This depends on slope and amount of precipitation.
 Sub-surface Flow: Infiltrated water that moves in the unsaturated zone of
the soil is sub-surface flow. Also called as interflow. It moves towards the
rivers. It depends on the soil type and its stratification in the area.
 Ground water Flow: Flow of water in the saturated zone of soil, below
ground water table. Darcy’s equation is applicable.
 River Flow: Flow of water in the rivers
 About 71 percent of the Earth's
HYDROLOGIC BUDGET surface is water-covered, and
the oceans hold about 96.5
percent of all Earth's water
 It is a balance between inflows, outflows and change in storage in a given
time Total water:1,386,000,000(km3)
Fresh Water:10,633,450 km3
 A water budget reflects the relationship between input and output Rivers & Lakes: 93,113 km3
of water through a region Atmospheric water:12,900 km3
 Total quantity of water available to earth is finite and indestructible Source: USGS Website
 Global hydrologic system may be considered as closed
 Open hydrologic sub-systems are abundant. For example, Rivers are dynamic,
open systems. They take water from the global hydrological cycle, use it in
their own local hydrological cycle and then return the water to the global
cycle.
 For any system water budget can be established
HYDROLOGIC BUDGET ELEMENTS for
WETLAND
HYDROLOGIC BUDGET ELEMENTS FOR A
REGION:

 A region is selected and budget is developed for that region. These regions
may be
 Topographically defined (e.g, watersheds and river basins)
 Politically specified (e.g., country or city limits)
 Or chosen on some other grounds

 Water Shed : an area of land bounded by ridges that contributes its water to
some drain, river, lake, or seas is called Watershed or Catchment Area.
 Watershed Boundary: line or boundary that separates the water flowing to
different rivers, basins or seas
WATERSHED AREA and WATERSHED BOUNDARY for
an OUTLET

OUT
LET
HYDROLOGIC BUDGET

Interception ET ET

Depression Channel
Interflow
storage Input

Aquifer Channel
Precipitation
Recharge Input
Infiltration
Deep
groundwater

Overland Channel
Flow Input
HYDROLOGIC BUDGET
(Inflows)

 Precipitation (P)
 Infiltration (I)
 From a water channel entering in
the area (R1)
 Ground water flowing into the
area from adjoining areas (G1)
 Ground water effluent to a
surface stream (Rg)
HYDROLOGIC BUDGET
(Outflows)

 Surface Runoff
 Export through water channel (R2)
 Evaporation
 From ground (Eg)
 From Surface(Es)
 Transpiration
 From ground (Tg)
 From Surface(Ts)
 Infiltration (I)
 Groundwater flowing out of the region (G2)
HYDROLOGICAL BUDGET
(Change in storage)

 Ground water
 Soil Moisture
 Surface reservoir water and depression
 Detention storage
HYDROLOGIC EQUATION
 Hydrologic budget Above The GROUND Surface
P+R1-R2+Rg-Es-Ts-I=∆Ss
 Hydrologic budget Below GROUND Surface
I+G1-G2-Rg-Eg-Tg= ∆Sg
 Total Hydrologic budget for the AREA (Above and below combined)
P-(R2-R1)-(G2-G1)-(ES+Eg)-(Ts+Tg) = ∆(Sg+ Ss)
 If the subscripts are dropped, and equation letters refer to total precipitation and
net values of: Surface flow, Underground flow, Evaporation, Transpiration and
Storage, then above equation is written as:
P-R-G-E-T=∆S
And in some simple cases, where terms G, E and T do not apply (or are insignificant) then
the budget equation reduces to:
P-R= ∆S any example??
APPLICATIONS OF THE HYDROLOGIC
EQUATION: Few Considerations
 Difficulty in solving practical problems lies mainly in the inability to measure or
estimate properly the various hydrologic equation terms.
 For local studies reliable estimates are often made but on global scale
quantification is crude.

 Precipitation is measured by rain gauges or snow gauges throughout area

 Surface flows can be measured using various devices such as weirs, flumes,
velocity meters and depth gauges
 Under good conditions these measurements are frequently 95% or more accurate
 Soil moisture can also be measured using neutron probes and gravimetric
methods (oven drying and weighing) infiltration can be determined infiltrometers
but the estimates are crude
APPLICATIONS OF THE HYDROLOGIC
EQUATION
HOWEVER:
 The extent and rate of movement of ground water is exceedingly difficult to
determine.
 Determination of quantities of evaporation and transpiration is also extremely
difficult.
 For the large drainage basins rate of evaporation, transpiration and
groundwater movement are often highly heterogeneous.
 In such cases hydrologic equation is a useful tool and can be employed in
various ways. For example it can be applied to estimate one unknown if rest
of component of budget equation are known
NUMERICAL PROBLEM

 In a given year, a 10,000-mi2 watershed received 20 inches of

precipitation. The average rate of flow measured in the river draining the
area was found to be 700 cfs( cubic feet per second). Make a rough
estimate of the combined amounts of water evaporated and transpired
from the region during the year of record.
 Solution:
P-R-G-E-T= ∆S
ET=P-R-G-∆S
ET=?
Assumptions :
 Groundwater inflow & outflow can be considered zero, if over a year ground
water table is constant.
 No change in surface storage over a year can also be assumed
 Equation becomes ET=P-R
 R=700cfs
 R= 0.95in
 P=20in
 ET=20-0.95
 ET=19.05in/year
NUMERICAL PROBLEM

 A= 25900 km2
 P=510mm
 R=20 cumecs
 E+T=?
 E+T=485.6mm
Water resources and water demands of
Pakistan.
Water Resources in Pakistan: Post Tarbela means after1976
Average Annual Inflows to the Indus Basin
Source Kharif(MAF) Rabi(MAF) Annual(MAF)
Historic 76.65 13.59 90.24
Indus
Post Tarbela 75.13 15.22 90.35
Historic 17.69 4.42 22.11
Jehlum
Post Tarbela 18.06 5.07 23.13
Historic 20.59 3.89 24.48
Chenab
Post Tarbela 22.38 4.77 27.15

Eastern Rivers Historic 8.85 1.36 10.21

(Ravi & Satluj) Post Tarbela 6.41 1.76 8.17
Historic 123.78 23.26 147.04
Total Inflows 148.8
Post Tarbela
121.98 26.82 (145 avg. of
(avg. 1976-2000)
1976-2013)
SURFACE WATER
Annual average
inflow
145 MAF (180 BCM)

Diverted to Canals System Losses Evaporation

Percolation
101 - 103 MAF (130 BCM) 10 MAF (12 BCM) Conveyance

Conveyance losses
40 MAF (50 BCM)

Water available at
farm gate 4 MAF Evaporation
61 MAF (75 BCM) 36 MAF Percolation

Flowing 30 MAF to
1/3rd Plant (ET) sea
1/3rd Percolation (40 BCM) Average Percolation per year ≈ 60 MAF
1/3rd Evaporation
 Average Water in Indus Basin Pakistan
All values in BCM (Billion m3)

Note: 1 BCM = 0.81 MAF

Ref:
Young, William J., Arif Anwar, Tousif Bhatti, Edoardo Borgomeo, Stephen Davies,
William R. Garthwaite III, E. Michael Gilmont, Christina Leb, Lucy Lytton, Ian
Makin, and Basharat Saeed. 2019. “Pakistan: Getting More from
Water.” Water Security Diagnostic. World Bank, Washington, DC.

BCM MAF
170 137.7
125 101.3
80 64.8
68 55.1
62 50.2
41 33.2
32 25.9
30 24.3
27 21.9
22 17.8
13 10.5
11 8.9
6 4.9
4 3.2
3 2.4
WATER APPORTIONMENT ACCORD (1991)
Key features:
Province Kharif (MAF) Rabi (MAF) Total (MAF)

Punjab 37.07 18.87 55.94

Sindh * 33.94 14.82 48.76

NWFP (a) 3.48 2.3 5.78

(b) Civil Canals **

Balochistan 2.85 1.02 3.87

Total 77.34 37.01 114.35

** 1.8 1.2 3

* Including already sanctioned Urban and Industrial uses for Metropolitan Karachi.

** Ungauged Civil Canals above the rim stations

 WATER DEMANDS BY VARIOUS SECTORS:
World vs PAKISTAN

High-Income Global Low and Medium

Countries Income Countries
11% 8%
30% 8% 10%
23%

82%
69%
59%

Agricultural Use
Pakistan: Agri:Domestic:Industry= 94%, 5%, 1% Domestic Use
Industrial Use
Water Availability and Demands in
Pakistan

Pakistan: Agri:Domestic:Industry= 94%, 5%, 1%

Ref: The Vulnerability of Pakistan’s Water Sector to the
Impacts of Climate Change: Identification of gaps and