TOPIC 1: WHY DO WE STUDY HYDROLOGY AND OPEN CHANNEL HYDRAULICS

Transcription

Unit CIV2262: Waterway Engineering
Topic 1: Why do we study hydrology and open channel hydraulics
1.1
TOPIC 1: WHY DO WE STUDY HYDROLOGY AND OPEN
CHANNEL HYDRAULICS
TABLE OF CONTENTS
1. PREVIEW .....................................................................................................................2
1.1. Introduction ........................................................................................................ 2
1.2. Objectives ........................................................................................................... 2
1.3. Readings ............................................................................................................. 3
2. WATER CYCLE...........................................................................................................3
2.1. Water Cycle Components................................................................................... 3
3. FLOODS........................................................................................................................6
4. RIVERS .........................................................................................................................7
5. SUMMARY ..................................................................................................................8
6. KEY CONCEPTS AND DEFINITIONS ......................................................................8
7. REFERENCES AND FURTHER READING ..............................................................9
8. REVIEW QUESTIONS ................................................................................................9
9. ANSWERS TO REVIEW QUESTIONS ....................................................................10
Department of Civil Engineering, Monash University
Edition Date: 7:03
1.2
1. PREVIEW
1.1. Introduction
The engineer invokes principles in order to deal with
problems that arise in practice, and when dealing with
these general principles he still remains in touch with
the physical events which have promoted the need to
generalize.
Henderson (Open channel Flow, 1966)
The aim of this topic to show you why it is important to study hydrology and open
channel hydraulics. There is a important engineering role in solving water engineering
problems in Australian and internationally. This topic explores some critical issues and
engineering approaches to their solution. We hope, this will make you interested in
learning more about hydrologic and hydraulic processes and design.
The topic starts by discussing the water cycle in nature and explaining which part of the
cycle will be the topic of this unit. Some basic statistics on water balance in nature are
presented. As case studies, we then explore two key issues, floods and river processes.
1.2. Objectives
The aim of the topic is to get you to love this unit!
After completing this topic you should be able:
To understand the reasons for studying hydrology;
To understand the reasons for studying open channel hydraulics;
To list some critical water management issues; and
To understand the role of engineers in managing these issues.
Edition Date: 7:03
1.3
1.3. Readings
For a overview water issues in Australia and the role of engineers it
is worth skimming one or more of these books:
SUGGESTED
J. M. Powell (1989) Watering the garden state : water, land and
community in Victoria, 1834-1988
333.91009945 P884W in the Hargrave or Matheson Libraries
Smith, D. I. (1999) Water in Australia. Oxford University Press
33.9100994 S645W in the Hargrave or Matheson Libraries
W. Boughton (1999) A Century of Water Resources Developments
in Australia. Institution of Engineers Australia
2. WATER CYCLE
2.1. Water Cycle Components
Total mass of water associated with our planet is fixed and exists in various phases and
locations, referred to as the water cycle (interaction of water with land and air).
Figure1.1: Water cycle
Edition Date: 7:03
1.4
Under several influences, of which heat is predominant, water is evaporated from both
water and land surfaces and is transpired from living cells. This vapour circulates
through the atmosphere and is precipitated in the form of rain or snow (Figure 1.1).
On striking the surface of the earth, the water follows two paths. In amounts determined
by the intensity of the rain and the porosity, permeability, thickness, and previous
moisture content of the soil, one part of the water, termed surface runoff, flows directly
into rills and streams and thence into oceans or landlocked bodies of water; the
remainder infiltrates into the soil. A part of the infiltrated water becomes soil moisture,
which may be evaporated directly or may move upward through the roots of vegetation
to be transpired from leaves. The portion of the water that overcomes the forces of
cohesion and adhesion in the soil profile percolates downward, accumulating in the socalled zone of saturation to form the groundwater reservoir, the surface of which is
known as the water table. Under natural conditions, the water table rises intermittently
in response to replenishment, or recharge, and then declines as a result of continuous
drainage into natural outlets such as springs.
2.2. Water Budget
Total water budget of the world: only 0.62% is accessible (0.01% in freshwater lakes
and rivers, and 0.61% in ground water).
Table 1.1.: Water Budget on the Planet
Cubic
kilometres
% Total
Water
125
104
1.2
67
8,350
29,300
0.009
0.008
0.0001
0.005
0.61
2.14
Sub-Total
37,800
2.80
Atmosphere
13
0.001
320,000
97.3
1,360,000
100
Water item
Land areas
Freshwater lakes
Saline lakes and inland seas
Rivers
Soil moisture and vadose water
Groundwater to 4,000m (13000 ft)
Icecaps and glaciers
World oceans
TOTAL
Edition Date: 7:03
1.5
Activity 1.1
(30 minutes)
Read about a Water Cycle on Internet.
Suggested links:
http://www.wrc.wa.gov.au/schools/water_cycle.html
http://ga.water.usgs.gov/edu/followdrip.html
http://www.watercare.net/wll_cc/cw_water_cycle_copy2.htm
We will be revisiting the water cycle later in the course.
2.2. Engineering the water cycle
In this course, we will mainly focussing on a small part of the water cycle:
Rainfall,
Surface runoff; and
Flow in rivers and open channels.
But think about all the issues these components influence:
Drought
Floods
Water supply to towns
Irrigation of farmland
Erosion
Drainage
In the Hydrology section of this unit our main interest will be floods, particularly how
design flood flows can be selected. For the Hydraulics part of the unit, the first part will
be on open channel hydraulics, leading to practical issues associated with measuring
flow and managing rivers.
Lets have a brief look at floods and rivers in the remainder of this introductory topic.
Edition Date: 7:03
1.6
3. FLOODS
(Curtesy, Aridflow project)
Figure1.2: Meeting in floodwaters at 40oC (Central Australia)
Floods can be defined as ‘relatively high water levels caused by excessive rainfall,
storm surge, dam-break or a tsunami that overtop the natural or artificial banks of a
stream, creek, river, estuary, lake or dam’ (SCARM, 2000). Floods must be expected
occasionally, resulting from the variability of climatic and hydrologic factors, but their
occurrence, nature and severity may vary significantly depending on the specific
conditions.
A flooding problem occurs when floodwaters disrupt normal activities. In extreme
cases, roads are cut, houses inundated and people drowned. On average, flood damage
costs Australia about $300 +/- 50 million per year (AWRC, 1992). The damage bill for
Victoria averages $56 million per year (DNRE, 1998). Engineers have a key role, in
understand floods and reducing the damage and disruption they cause.
Later in the unit, you will learn how to analyse flood flows and predict the probability
of occurrence of future floods.
Activity 1.2
(20 minutes)
Read about a famous flood that happened in Australia.
The Bureau of Meteorology has brief descriptions of historical floods:
http://www.bom.gov.au/lam/climate/levelthree/c20thc/flood.htm
Edition Date: 7:03
1.7
4. RIVERS
Figure1.3: Structures to encourage bed scour and improve habitat (Creightons Creek,
Victoria)
Rivers have been a major component of human activity since man first appeared on
earth. Transport, water supply and waste disposal are but three of the many uses of
rivers. Although there are many benefits to be obtained from rivers, they have also been
the source of much human misery and tragedy. Floods and other river disasters are
perhaps even increasing in frequency in many parts of the world as river training
schemes and land use changes are implemented.
Engineers and scientists have studied rivers for centuries, fascinated by the self-formed
geometric shapes and the response of the rivers to changes in nature and human
interference. Indeed, although few other subjects have been studied as extensively as
rivers, some major aspects of the hydraulics, sedimentation and fluvial processes have
become clear only very recently, while the explanations for others remain elusive.
As engineers we are involved in water supply, channel design, flood control, river
regulation, navigation improvement and many other aspects which involve the
imposition of controls on natural river behaviour. It has become clear in recent times
that rivers cannot be mastered by force, but instead can be utilised for the good of
humankind only by understanding. Such understanding has become critically important
in recent years as environmental issues and concerns have become more prominent.
Edition Date: 7:03
1.8
Historically, rivers have been grossly abused by human activity. Rivers have been used
as the ultimate sink for pollution – “out of sight, out of mind” – and have suffered major
degradation through changes in flow regime and river course and through interruption
of natural processes such as sediment transport. As a result, many once-pristine rivers
are now no more than drains, devoid of indigenous fish and aquatic plant species.
Activity 1.3
(30 minutes)
Read about river restoration in Australia
http://www.wrc.wa.gov.au/protect/waterways/casestudies_mwg.html
http://www.rivers.gov.au/publicat/riprap/riprap15.htm
5. SUMMARY
This topic is meant to set the scene for the rest of Civ 2262 by highlighting some key
water issues and the role of engineers in their management.
The water cycle shows the various forms that water takes and the movement between
these forms. In this unit we will be mainly concerned with rainfall and surface flow.
The practical application of the material you will cover in this unit will be useful in
many areas of civil engineering practice but two areas are particularly highlighted here,
floods and rivers. Slides presented during the lecture will further explore these issues
and the role of engineers.
6. KEY CONCEPTS AND DEFINITIONS
Floods - relatively high water levels caused by excessive rainfall, storm surge, dambreak or a tsunami that overtop the natural or artificial banks of a stream, creek, river,
estuary, lake or dam (SCARM, 2000).
Hydraulics – The study of the mechanics of fluids.
Hydrology is concerned with the waters of the earth - their occurrence, circulation, and
distribution, their chemical and physical properties, and their reaction with their
environment, including their relation to living things (US Committee for Scientific
Hydrology, 1962).
Edition Date: 7:03
1.9
River rehabilitation – intervening in a degraded river to enhance its aesthetic,
ecological condition, or to move it toward a more desirable state.
Water cycle (refer to figure 1.1)
7. REFERENCES AND FURTHER READING
AWRC (Australian Water Resources Council) (1992) Floodplain Management in
Australia. Water Management Series No. 21. Australian Government Publishing
Service.
Boughton, W. (1999) A Century of Water Resources Developments in Australia..
Institution of Engineers Australia
DNRE (Department of Natural Resources and Environment) (1998) Victoria: flood
management strategy.
Powell, J. M. (1989) Watering the garden state : water, land and community in Victoria,
1834-1988 333.91009945 P884W in the Hargrave or Matheson Libraries
SCARM (2000). Floodplain management in Australia – best practice principles and
guidelines. Standing Committee on Agriculture and Resource Management (SCARM)
Report 73, CSIRO Publishing, Collingwood, Australia, 101 pages.
Smith, D. I. (1999) Water in Australia. Resources and Management. Oxford University
Press.
Standing Committee on Rivers and Catchments (1991) Guidelines for Stabilising
Waterways. Rural Water Commission of Victoria.
8. REVIEW QUESTIONS
1. If the average annual flood damage in Victoria is $56 million per year,
approximately how much damage would you expect to occur in a large flood
event?
2. There is much discussion about a water shortage but are we ever going to run
out of water?
3. Has Gardners Creek (north of Monash University) changed much or is it about
the same as it was when Europeans first arrived?
4. What about the Yarra River. Is it in a natural or modified condition?
5. Is river management such an important issue that it has influenced the outcomes
of elections in Australia?
Edition Date: 7:03
1.10
9. ANSWERS TO REVIEW QUESTIONS
1. Large floods might happen about every 5 years or so somewhere in the state so
the damage bill could be $250 - $300 million. The total direct cost of damage
was $320 million for the 1993 floods in Victoria (DNRE, 1998).
2. Water shortages are a problem of cost and distribution. There is plenty of water
in the oceans, but it isn't cheap to desalinate it and transport it to where it is
needed (see Table 1.1).
3. Gardners Creek has been greatly altered from natural. Almost the entire creek
has been lined with rock or concrete to reduce erosion caused by increased flood
flows from urbanisation. Increased flows also mean the creek is much larger
than natural.
4. The Yarra has also changed a lot although it is not as obvious as Gardeners
Creek. There is now much less flow as about half the water is taking out for
drinking. There have also been major realignments. The Yarra used to flow
though the botanical gardens but was realigned and an ornamental lake remains.
There were rapids in the city near Flinders Street, but these where blown up to
improve navigation. Herron Island in Burnley was formed when water flooded
an old quarry site.
5. River related issues have played a big part in at least three elections. In the 1999
Victorian Election, concerns about the Snowy River contributed to the defeat of
the national party candidate in Gippsland East and the election of an independent
(Craig Ingram) who voted with Labor in State Parliament. In the 1983 federal
election there was huge public opposition to plans to construct a dam on the
Gordon River in Tasmania which would have flooded parts of the Franklin
River. The federal Labor party opposed the dam and won the election. In South
Australia in 1970 the Labor party won the 1970 election after campaigning on a
platform of building a dam on the Murray River at Chowilla in South Australia.
It was never actually built.
Edition Date: 7:03

TOPIC 1: WHY DO WE STUDY HYDROLOGY AND OPEN CHANNEL HYDRAULICS

Transcription

Similar documents

Sun Hydraulics` First Publication in pdf format

listing PDF

Kes Zapkus at Andre Zarre

Full text

SLMP year end presentation - Sproat Lake Community Association

PDF - Bryant Real Estate

PDF - Monex Europe

Buy from a Range of Mens Clothing in Australia

PDF

What Matters? The Peak, the Volume and the Duration of Floods