Dr. Mujahid Khan, UET Peshawar

Hydrology and Water Management

2

Course Outline

• Hydrologic Cycle and its Processes

• Water Balance Approach

• Estimation and Analysis of Precipitation Data

• Infiltration and Runoff Phenomena

• Application of TR55 model for Runoff Estimation

• Measurement of Stream Flow and Stage Discharge

Relationships

• Unit Hydrograph Theory and its Application

• Flood Flow Routing and its Application

• Frequency Analysis

• Application of HEC-HMS model

3

The study of water, including rain, snow and water on the earth’s surface, covering its properties, distribution, utilisation, etc.

(Chambers Science and Technology Dictionary)

The study of water in all its forms, and from its origins to all its destinations on the earth.

(Bras, 1990)

The science dealing with the waters of the earth, their occurrence, distribution and circulation, their chemical and physical properties, and their interaction with the environment.

(Ward & Robinson, 1999)

HYDROLOGY

4

Main Branches

HYDROLOGY

Ground Water

Hydrology

Surface Water

Hydrology

5

Water is one of the most valuable natural resources essential for human

and animal life, industry and agriculture.

The study of hydrology helps us to know

(i) The maximum probable flood that may occur at a given site and

its frequency; this is required for the safe design of drains and

culverts, dams and reservoirs, channels and other flood control

structures.

(ii) The water yield from a basin—its occurrence, quantity and

frequency, etc. this is necessary for the design of dams, municipal

water supply, water power, river navigation, etc.

(iii)The ground water development for which a knowledge of the

hydrogeology of the area, i.e., of the formation soil, recharge

facilities like streams and reservoirs, rainfall pattern, climate, cropping

pattern, etc. are required.

(iv)The maximum intensity of storm and its frequency for the design of

a drainage project in the area.

Scope of Hydrology

6

Engineering Hydrology

• It uses hydrologic principles in the solution of engineering

problems arising from human exploitation of water

resources of the earth.

• The engineering Hydrologist, or water resources engineer,

is involved in the planning, analysis, design, construction

and operation of projects for the control, utilization and

management of water resources.

• Hydrologic calculations are estimates because mostly the

empirical and approximate nature of methods are used to

describe various hydrological processes.

7

Quantity of water available from a catchment ?

Quality of water in a catchment eg. sediment & phosphate content ?

Problems Related to Hydrology

8

Peak discharge expected in a stream during a storm ?

9

The design of hydraulic structures eg. dams/ reservoirs, bridges

10

Damage caused by peak floods

11

Engineering Hydrology seeks to answer questions of the following types:

• What is the maximum probable flood at a proposed dam site?

• How does a catchment’s water yield vary from season to season and from year to

year?

• What is the relationship between a catchment’s surface water and groundwater

resources?

• What flood flows can be expected over a spillway, at a highway culvert, or in an

urban storm drainage system?

• What reservoir capacity is required to assure adequate water for irrigation or

municipal water supply in droughts condition?

• What hydrologic hardware (e.g. rain gauges, stream gauges etc) and software

(computer models) are needed for real-time flood forecasting?

Uses of Engineering Hydrology

12

• In seeking answers to these questions, Engineering

Hydrology uses various Measurement and Analysis

techniques.

• Hydrological Measurements

Deals with the measurement of water in the different phases

of hydrological cycle such as rainfall and stream gauging.

• Hydrological Analysis

Aims to develop a methodology to quantify a certain phase

or phases of hydrologic cycle – for instance, precipitation,

infiltration, or surface runoff.

Hydrologic Measurement and Analysis

13

HYDROLOGIC CYCLE

• The hydrologic cycle describes the continues re-circulating

transport of the waters of the earth, linking atmosphere, land and

oceans.

• To explain it briefly, water evaporates from the ocean surface,

driven by energy from the Sun, and joins the atmosphere,

moving inland as clouds. Once inland, atmospheric conditions

act to condense and precipitate water onto the land surface,

where, driven by gravitational forces, it returns to the ocean

through river and streams.

• The process is quite complex, containing many sub-cycles.

• Engineering Hydrology takes a quantitative view of the

hydrologic cycle.

14

Hydrological Cycle

15

16

• The quantification of the hydrologic cycle which is an

open system, can be represented by a mass balance

equation, where inputs minus outputs are equal to the

change in storage.

I - O = DS It is a basic Hydrologic Principle or equation that may be

applied either on global or regional scale.

• The water holding elements of the hydrological cycle are:

1. Atmosphere 2. Vegetation

3. Snow packs 4. Land surface

5. Soil 6. Streams, lakes and rivers

7. Aquifers 8 Oceans

Hydrologic Cycle

17

Hydrological Processes

• Precipitation

• Interception

• Evaporation

• Transpiration

• Infiltration

• Overland flow

• Sub Surface flow (P-96)

• Groundwater outflow

18

19

Evapotranspiration from l and

Evaporati on from ocean

Moi sture ove r land

Pre ci pitati on on l and

100

61

39

424

Pre ci pitati on on oce an

385

Groundwate r outfl ow

Surface outfl ow38

1

Surface flow

Groundwate r fl ow

Infi ltrati on

Global Water Balance of

The hydrological cycle

20

In the atmosphere:

Precipitation (P) = Evapotranspiration (ET)

100+385 = 61+424

On land:

P = Evapotranspiration (ET) + Surface runoff (R) +

Groundwater outflow

100 = 61 + 38 + 1

Over oceans and seas:

Ocean precipitation + Surface runoff + Groundwater

outflow = Evaporation (E)

385 + 38 + 1 = 424

Global Water Balance

21

Table 1. Estimated Distribution of World's Water.

Component Volume 1000 km3 % of Total Water

Atmospheric water 13 0.001

Surface Water

Salt Water in Oceans

Salt water in lakes & inland seas

Fresh water in lakes

Fresh water in stream channels

Fresh water in glaciers and icecaps

Water in the biomass

1320000

104

125

1.25

29000

50

97.2

0.008

0.009

0.0001

2.15

0.004

Subsurface water

Vadose water

G/W within depth of 0.8 km

G/W between 0.8 and 4 km depth

67

4200

4200

0.005

0.31

0.31

Total (rounded) 1360000 100

22

Hydrologic Systems

• Chow, Maidment, and Mays (1988) defined a hydrologic system as a

structure or volume in space, surrounded by a boundary, that accepts

water and other inputs, operates on them internally, and produces them

as outputs.

• The structure (for surface or subsurface flow) or volume in space (for

atmospheric moisture flow) is the totality of the flow paths through

which the water may pass as throughout from the point it enters the

system to the point it leaves.

• The boundary is a continuous surface defined in three dimensions

enclosing the volume or structure.

• A working medium enters the system as input, interacts with the

structure and other media, and leaves as output.

• Physical, chemical and biological processes operate on the working

media within the system; the most common working media involved in

hydrologic analysis are water, air and heat energy.

23

Mass Balance in Hydrologic Systems

• General form:

Rate of accumulation of mass in system =

Input rate - output rate ± reaction

• Hydrologists:

Change in storage = Inflow – Outflow

• Assumptions:

– no reaction

– volume, pressure, temperature do not change

24

Inflow: 1. Precipitation

2. Import defined as water channeled into a given area.

3. Groundwater inflow from adjoining areas.

Outflow: 1. Surface runoff outflow

2. Export defined as water channeled out of the same area.

3. Evaporation

4. Transpiration

5. Interception

Change in Storage: This occurs as change in:

1. Groundwater

2. Soil moisture

3. Surface reservoir water and depression storage

4. Detention Storage

Water Balance Components

25

Global Hydrologic Cycle

• The global hydrologic cycle can be represented as a system

containing three subsystems:

the atmospheric water system,

the surface water system, and

the subsurface water system.

• Block-diagram (flow chart) representation of GHC is shown

in Figure#1.

26

Precipitation

Infiltration

Transpiration

Interception

Groundwater

recharge

Overland flow

Subsurface flow

Runoff to streams

and ocean Surface runoff

Groundwater

flow

Evaporation

Atm

osp

her

ic W

ate

r S

ub

surf

ace

Wa

ter

Su

rfa

ce

Wa

ter

Block-diagram representation of the global hydrologic system (Chow et al. 1988).

27

Regional Water Balance (Water Budget) Precipitation (P) Evapotranspiration (ET)

Surface

runoff (R)

Infiltration (F)

A mass balance over time from t = 0 to T, i.e. Inputs - Outputs = Change in Storage

P - (R+ET+F) = ΔS

All terms in the hydrologic equation should be in the same units.

28

Infiltration (F)

Storage (S)

Time t = 0

Time t = T

Change in storage (DS)

Precipitation (P) Evapotranspiration (ET)

Surface runoff (R)

Schematic representation of the mass balance equation

DS = P - (R + F + ET)

DS = +ve if P > (R + F + ET)

DS = -ve if P < (R + F + ET)

DS = 0 if P = (R + F + ET)

29

Catchment and Basin

• A catchment is a portion of the earth’s surface that

collects runoff and concentrates it at its furthest

downstream point, referred to as the catchment outlet.

• The runoff concentrated by a catchment flows either into

a larger catchment or into the ocean.

• The place where a stream enters a larger stream or body

of water is referred to as the mouth.

• The terms watershed and basin are commonly used to

refer to catchments. Generally, watershed is used to

describe a small catchment (stream watershed), whereas

basin is reserved for large catchments (river basins).

30

• The watershed or basin is defined by the surrounding

topography, the perimeter of which is called a divide.

• It is the highest elevation surrounding the watershed.

• All of the water that falls on the inside of the divide has the

potential to be shed into the streams of the basin encompassed

by the divide. Water falling outside of the divide is shed to

another basin.

• The water flowing in streams is called stream flow.

Watershed and Stream

31

• Horton suggested a classification of stream order as a

measure of the amount of branching within a basin.

• A first order stream is a small, unbranched tributary.

• A second order stream has only first order tributaries.

• A third order stream has first and second order tributaries and

so on.

• When a channel of lower order joins a channel of higher order,

the channel downstream retains the higher of the two orders.

Stream Order

32

Figure 1. Stream Orders of a Watershed.

Divide

1

1

1 1

1

1

1

1 1

1

1

2

2 2

2

2

1

2

3

3

3 4

4

2 1

1

33

Watershed Characteristics

Size

Slope

Shape

Soil type

Storage capacity

Reservoir

Divide

Natural

stream

Urban

Concrete

channel

34

For the analysis and design of any hydrologic project adequate data and length of records are

necessary. A hydrologist is often posed with lack of adequate data. The basic hydrological data

required are:

(i) Climatological data

(ii) Hydrometeorological data like temperature, wind velocity, humidity, etc.

(iii) Precipitation records

(iv) Stream-flow records

(v) Seasonal fluctuation of ground water table or piezometric heads

(vi) Evaporation data

(vii) Cropping pattern, crops and their consumptive use

(viii) Water quality data of surface streams and ground water

(ix) Geomorphologic studies of the basin, like area, shape and slope of the basin, mean and median

elevation, mean temperature (as well as highest and lowest temperature recorded) and other

physiographic characteristics of the basin; stream density and drainage density; tanks and reservoirs

(x) Hydrometeorological characteristics of basin:

i. (Depth-area-duration (DAD) curves for critical storms (station equipped with self-recording

raingauges).

ii. Isohyetal maps—Isohyets may be drawn for long-term average, annual and monthly precipitation

for individual years and months

iii. Cropping pattern—crops and their seasons

iv. Daily, monthly and annual evaporation from water surfaces in the basin

v. Water balance studies of the basin

vi. Soil conservation and methods of flood control

HYDROLOGICAL DATA

35

In a given year, a catchment with an area of 2500 km2 received

1.3 m of precipitation. The average rate of flow measured in a

river draining the catchment was 30 m3s-1.

(i). How much total river runoff occurred in the year (in m3)?

(ii). What is the runoff coefficient?

(iii).How much water is lost due to the combined effects of

evaporation, transpiration, and infiltration. (Express in m).

Problem #1

36

Solution

(i). Total runoff volume

= number of seconds in a year average flow rate

= 31 536 000 30

= 9.4608108 m3

(ii). Runoff coefficient

= runoff volume/ precipitation volume

= (9.4608108) / (1.3 2500 106)

= 0.29 (29 %)

Problem #1

37

(iii). The water balance equation can be arranged to produce:

ET+F= P - R - ΔS

where:

P = (1.3 2500106)

= 3.25109 m3

R = 9.4608108 m3 (from [i])

ΔS = 0 (i.e. no change in storage)

So,

ET + F = 3.25109 - 9.4608108

= 2.30392109 m3

= (2.30392109) / (2500106)

= 0.92 m

Problem #1

38

In a given year, a catchment with an area of 1750 km2 received 1250

mm of precipitation. The average rate of flow measured in a river

draining the catchment was 25 m3s-1.

(i). Calculate how much total river runoff occurred in the year

(in m3).

(ii). Calculate the runoff coefficient. What is the percentage

runoff ?

Problem #2

Area of the catchment = 1750 km2 = 1750 x 10^6 m2

Flow rate in the river = 25 m3/s

Precipitation received = 1250 mm = 1.25 m

39

Solution:

Total runoff volume = 31 536 000 x 25

= 788.4 x 10^6 m3

Total annual precipitation = (1.25) x (1750 x 10^6)

= 2187.5 x 10^6 m3

Flow rate during the year = 2187.5 x 10^6 / (365 x 24 x 60 x 60)

= 69.36 m3/s

Runoff Coefficient = Actual flow in river / Total

precipitation occurred

= 25 / 69.36

= 0.36

Percentage of flow = 0.36 x 100 = 36%

Problem #2

40

Problem #3

A lake has a surface area of 708,000 m2. In May, the River A

flows into the lake at an average rate of 1.5 m3/s. River B

flows out of lake at an average rate of 1.25 m3/s. The

evaporation rate was measured as 14.0 cm/month. A total of

22.5 cm of precipitation fell in May. Seepage losses are

negligible. The average depth in the lake on May 1 was 19 m.

What was the average depth on May 30th?

• Surface area of lake = A = 708,000 m2

• Average depth on May 1 = 19 m

41

• Inputs to the lake

Average inflow = I = 1.5 m3/s = 3,888,000 m3/mo

Precipitation = P = 22.5 cm/month = 159,300 m3/mo

• Outputs to the lake

Average outflow = O = 1.25 m3/s = 3,240,000 m3/mo

Evaporation = E = 14.0 cm/month = 99,300 m3/mo

Seepage = 0

Problem #3

Mass Balance equation:

Change in volume of water in the lake during this month =

DS = change in storage =

Inflow - Outflow + Precipitation - Evaporation

42

• DS = I – O + P – E =

= 3,888,000 m3/mo – 3,240,000 m3/mo

+ 159,300 m3/mo – 99,300 m3/mo

• DS = 708,000 m3/mo

Problem #3

• Since DS = 708,000 m3/mo and the average surface area

is 708,000 m2, the change in depth during the month

= (708,000 m3/mo)/708,000 m2 = 1 m or about 3.25 ft.

• Note DS is positive, this means that the volume increases

and therefore the depth increases. The new average depth

on May 30th would be 20 m.