How Clean is that Water?
Engineering Connection
Engineers make sure that our water supply is safe to drink and use. Environmental and civil engineers guard the quality of our water resources in many ways. They design water and sewage treatment plants that clean water for human use, and design industrial systems and filters that make sure factory-released water is not polluting. They also monitor surface and aquifer water levels and quality, and mitigate any damaging impact from irrigation, fertilizer, pesticide, chemical and industrial wastes.
What's wrong with this picture?
Do you think the stream is cleaner above or below the house?
Do the community residents have a direct impact on the water quality of the stream?
The people who live just down stream from the houses in use the stream as the source of their drinking water. Should they drink the water?
Other then drinking water, for what other purpose can streams be used?
Introduction/Motivation
Have you ever walked or driven by a polluted stream and looked at it in disgust? Have you taken a drink of water from a fountain and turned up your nose in distaste? Clean water is important to a person's health and lifestyle, and it is engineers who insure that our water is safe to drink and use. Environmental and civil engineers help maintain the quality of our water resources. They design treatment plants, monitor surface and groundwater, work with streams to sanitize drinking water, as well as deal with the prevention of streams from disappearing altogether from irrigation and industrial waste inputs.
Engineers have been involved with water regulation for quite a while. Rivers and streams have been modified since ancient times to regulate boat and barge traffic, to prevent flooding of populated areas, and to be redirected for drinking water purposes. The earliest known irrigation ditches, in Egypt, date to 3200 BC. Engineers of ancient Rome constructed the famous aqueducts from flowing water. The ancient Romans also created ditches — that still exist across the nation today (see Figure 2) — to move water from one area to another and to carry away waste products.
The Hayden-Rhodes Aqueduct in Arizona. (Central Arizona Project)
From about 1750-1900, Europe developed regulation schemes for almost all of its large rivers. From 1900-1940, there was a boom in dam building in North America, Southeast Asia and Europe. Hoover Dam, on the Colorado River in Boulder City, Nevada, was completed in 1936 and still ranks 14th in height and 23rd in volume among world dams. The period from 1950 to 1980 marks the peak of popularity in dam building, and today the practice has slowed to a pace of about 500 dams per year.
How many of you have been to a local stream and really looked at it?
Have you ever seen a fish in a stream?
What about an insect or a plant?
Stream water has many different characteristics and many different creatures living in it. What have you seen that might indicate a healthy or unhealthy stream? For example, lots of fish = healthy; lots of trash in the water = unhealthy. Many different species benefit from healthy water, including humans and animals that drink from the water.
Name the many uses for streams and rivers. For example, recreation (boating, canoeing, swimming), fishing, drinking water supply, crop irrigation, stock/animal water supply, education and scientific studies.
It is important to keep streams and rivers healthy for all of these different uses. Water removal from irrigation and diversions reduces river flow and alters the quality of the water habitat. Also, pollution from organic wastes (fertilizers, human waste water, etc.) and industrial wastes have decreased in the last 20 years, but still remain a great threat to the water quality of a stream or river. These are the challenges that engineers face daily.
What is water quality?
Water quality is commonly defined by its biological, physical, chemical and aesthetic (appearance and smell) characteristics. A healthy environment is one in which the water quality supports a rich and varied community of organisms and does not harm public health. The water quality of a body of water influences the way in which communities use the water for activities such as drinking, swimming or commercial purposes. It is an important environmental, economic and social resource in our world.
What are some indicators of water quality?
Water quality can be evaluated by how many and how varied the biota (living organisms) is in a stream. There are many factors that are important to the biota that use the stream. The chemical factors that influence the biota are dissolved major ions, dissolved nutrients, dissolved organic matter, dissolved gases (oxygen, carbon dioxide) and trace metals. Variation in these factors is determined by the type and amount of rocks, weathering, precipitation type and amount, and proximity to the sea. Seasonality also has an influence on chemical factors. Areas of high rainfall and surface water runoff have more dilute stream water compared to areas that are arid and have greater evaporation. Biological influences of these factors are normally seen only during times of extreme change. For example, anthropogenic (human) inputs of pollution or wastes may change the stream water chemistry to a pH below 5.0, which would drastically affect the flora and fauna.
Physical factors of a stream also influence the biota that uses the stream. Many physical factors provide challenges as well as benefits for the flora and fauna that inhabit the area. Current (how fast the stream moves), substrate (rock, stream bed and gravel), and temperature are a few of the more prominent physical factors. Current can provide transportation for organisms, but also poses the risk of the organisms being swept away. The substrates in a stream may provide shelter for a fish from the current or its enemies, and may determine the types of plants and algae that can grow there.
The water temperature affects growth rates, productivity and life cycles of the organisms in a stream system.
Oxygen, a chemical factor, is affected by all of these physical factors. Current replenishes oxygen in the system by bringing the water into contact with air. Temperature affects the amount of oxygen in the stream because solubility of oxygen in water decreases as temperature increases. Lastly, certain organisms breathe better in certain environments.