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

Transcription

1 Unit CIV2262: Waterway Engineering 1.1 TOPIC 1: WHY DO WE STUDY HYDROLOGY AND OPEN CHANNEL HYDRAULICS TABLE OF CONTENTS 1. PREVIEW Introduction Objectives Readings WATER CYCLE Water Cycle Components FLOODS RIVERS SUMMARY KEY CONCEPTS AND DEFINITIONS REFERENCES AND FURTHER READING REVIEW QUESTIONS ANSWERS TO REVIEW QUESTIONS...10

2 Unit CIV2262: Waterway Engineering 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 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.

3 Unit CIV2262: Waterway Engineering Readings SUGGESTED For a overview water issues in Australia and the role of engineers it is worth skimming one or more of these books: J. M. Powell (1989) Watering the garden state : water, land and community in Victoria, P884W in the Hargrave or Matheson Libraries Smith, D. I. (1999) Water in Australia. Oxford University Press 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

4 Unit CIV2262: Waterway Engineering 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 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 % Total Water item kilometres Water Land areas Freshwater lakes Saline lakes and inland seas Rivers Soil moisture and vadose water Groundwater to 4,000m (13000 ft) 8, Icecaps and glaciers 29, Sub-Total 37, Atmosphere World oceans 320, TOTAL 1,360,

5 Unit CIV2262: Waterway Engineering 1.5 Activity 1.1 (30 minutes) Read about a Water Cycle on Internet. Suggested links: We will be revisiting the water cycle later in the course 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.

6 Unit CIV2262: Waterway Engineering FLOODS (Curtesy, Aridflow project) Figure1.2: Meeting in floodwaters at 40 o C (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:

7 Unit CIV2262: Waterway Engineering 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.

8 Unit CIV2262: Waterway Engineering 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 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).

9 Unit CIV2262: Waterway Engineering 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, 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?

10 Unit CIV2262: Waterway Engineering 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.