Johnston County, North Carolina
We all live in a watershed! Animals and plants live there with us. Everyone affects what happens in a watershed by how we treat the natural resources in the watershed. So, what is a watershed? A watershed is the land area that drains water to a stream, river, lake or ocean. Water travels over the Earth's surface across forest land, farm land, pasture land, suburban land, neighborhood front yards and back yards, city streets and parking lots. Or, the water can seep into the soil to an aquifer and make its way to a stream via groundwater. Watersheds come in many different shapes and sizes. Some watersheds contain mountains and hills and some are nearly flat. A watershed can be affected by many different human activities and natural events. The routine of our everyday lives can affect the quantity and quality of water flowing in a watershed. Construction work, farming, logging, and the application and disposal of many garden and household chemicals can affect the health of a watershed.
Floods are a major natural event that occurs in watershed. Floods occur when the volume of water exceeds the ability of a stream, creek or river to hold the water within its normal banks. Any stream, creek, lake or river can flood. The size or magnitude of a flood is called 'recurrence interval'. By studying long periods of flow records for a stream or river, it is possible to estimate the size of a flood that would, for example, have a 100-year recurrence interval, thus being called a hundred year flood. This means that on the average, a particular stream or river would flood every 100 years. However, there is a chance that a 100-year flood could happen any time. The severity of a flood is often determined by loss of human life or property, which is usually directionally proportionate to the amount of human development in the flood plain surrounding the river or stream. A flood plain is a strip of fairly flat land bordering a stream, river or lake that usually holds or carries the overflow of flood waters. Flood plains are Nature's way of taking care of flood waters. Because they are flat areas, they are often ideal sites for construction and development.
Watershed come in many shapes and sizes. Larger watersheds are composed of many smaller watersheds. This watershed is a sub watershed of a larger watershed that has unplanned development. A watershed is determined by connecting the highest topographic points on a map between two adjacent areas. These points form a watershed boundary, similar to the edge of a bowl.
The quantity and quality of water draining from a watershed are dependent upon the climate, vegetation, soils, geology, and development within that watershed. Activities that change the vegetation, soils, geology, and surface characteristics of some watersheds will affect the quantity and quality of water contributed to a stream. For example, a greater volume of water, perhaps of poorer quality, will flow from a parking lot than from a forest or pasture, which may result in increased flooding in a watershed because the greater volume exceeds the natural ability of the stream to transport the water.
Underdeveloped watersheds are drainage basins that have no development affecting the quality or quantity of water in that watershed. These watersheds are primarily on public-owned lands in national forests, national parks, and wilderness areas. Underdeveloped watersheds provide scientists with areas to study the natural processes of a watershed and the movement of water within a watershed.
Planning the development within a watershed requires consideration of the entire drainage basin. Planned actions that consider the effect on the natural resources of the watershed will help preserve the quality and quantity of water flowing from a watershed. Actions such as controlling surface runoff from streets, providing recycling centers, farming along the contours, and logging practices that include controlling runoff and protecting stream channels help preserve the quality and quantity of water flowing from a watershed. Limiting the number and type of structures on a flood plain is one method of preventing loss of property from floods. Placing parks, golf courses, or farmland on a floodplain can reduce property loss caused by floods.
Unplanned development within a watershed has the potential for degradation of water quality and increased loss of property from flooding. Runoff from city streets, improper farming and logging techniques, and poor residential and industrial chemical-disposal practices all can affect water quality. Locating homes and businesses on flood plains greatly increase the chance of damage from flooding. In some places, flood-control structures such as dams and levees are required to protect development already located on the flood plain.
A watershed is an area of land that drains to a stream, river, lake or ocean. It is a land surface feature that can be identified by connecting the highest elevations between two areas. For example, a pitched roof of a house or a building is usually divided by a ridge. The back part of the roof is a separate watershed from the front part of the roof. During rainstorms, some water runs off both parts of the roof but meets in the street. Rain water from other houses in the neighborhood also flow into the street. Water from the street flows to a drain, ditch, or stream. Thus, the street is a larger watershed consisting of several smaller watersheds.
Floods occur when the level of a stream, river, or lake exceeds its normal height. Any stream or river can flood. During floods, water flows over the banks of a stream and into the surrounding low-lying areas called flood plains. During flooding, the threat to life and property damage most often occurs in the flood plain. Limiting the development within the flood plain is the best way to reduce damage associated with flooding.
The following activity is designed to demonstrate a watershed and the connection between small watersheds and larger watersheds. The activity also demonstrates property damage control during flooding through the placement of buildings in a flood plain.
Objectives - Students Will:
Materials - Each Group Will Need:
Have students examine other groups' models. How are they alike and how are they different?
Have students write a short essay discussing what they learned about watersheds and floods. As part of the essay, have them draw a picture of a watershed including the stream and associated flood plains. Also have students discuss where the best places to build homes within their watershed would be in order to avoid flooding.
Aquifer - An underground body of porous sand, gravel, or fractured rock filled with water and capable of supplying useful quantities of water to a well or a spring.
Drainage basin - Land area drained by a river.
Flood - Any relatively high flow of water that overflows natural or artificial banks of a stream, river, lake, or body of water.
Flood plain - A strip of relatively flat land bordering a stream, river or lake that conveys the overflow of flood waters.
Ground water - Water found in pores or cracks in sand, gravel, and rock beneath the land surface.
Precipitation - Rain, snow, hail. or sleet.
Recurrence interval - The average interval of time within which the magnitude of a given event, such as a flood, will be equaled or exceeded one time.
Runoff - That part of precipitation that appears in surface-water bodies.
Watershed - The land area that drains water to a stream, river, lake, or ocean.