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|Terms: Hydrosphere, hydrology, water cycle, interior and exterior drainage system, drainage basin, stream, aquifer, aquitard, zones of aeration and saturation, base level, alluvial fan, delta, evapotranspiration, load, perennial stream, gaining and losing streams, hydrograph, BOD, point source and diffuse source of pollution|
The .0221% that makes up water
on land is the water available for use. The two major reservoirs
through which terrestrial water circulates are on
the surface (surface water) and
in the ground (ground water). During a storm runoff flowing
over land percolates into the ground water system. This
re-emerges in streams
lakes or is discharged directly into the ocean. It's the surface water that
is largely responsible for the erosion of mountains and deposition sediment
and the ocean.
Over 90% of
ocean is carried by streams. Most terrestrial water systems have an exterior
drainage, which means they
terminate in the ocean. However, some systems, known as interior
systems, terminate in a saline
Surface water includes all water in streams, lakes, and overland flow(runoff). Surface water systems typically include a drainage basin (tributary network), a main stream (transportation system), and delta (distributary system) or in the case of an arid interior system an alluvial fan. A Drainage basin, or watershed, is the entire area drained by a stream and its tributaries. A large drainage basin, such as the Mississippi basin, is composed of a hierarchy of smaller basins, such as the Ohio and Missouri river basins.A delta forms where the main stream reaches base level (e.g. the ocean). At this point deposition causes the main trunk to bifurcate into a number of distributary branches that composed the delta.
Base level is the elevation below which a stream cannot erode. The ultimate base level, such as that for the Mississippi River is the ocean. At this point both the stream gradient and flow velocity required to carry sediment become zero. Any sediment carried to a base level is deposited. A local base level, such as a lake or another stream, controls the depth of erosion of the stream flowing into it. For example, the base level of the Missouri River is the Mississippi River.
Figure 1. Mississippi Drainage Basin drains the interior of North America and contains a number of smaller drainages, such as the Missouri and Ohio rivers. The Mississippi delta is deposited in the Gulf of Mexico, the base level for the Mississippi River.(Modified from figure 16.4, Earth Revealed)
A hydrologic divide is boundaries across which water cannot flow. There are three types of divides, topographic, recharge and discharge divides.
- Topographic divides are topographically high areas between watershed. The perimeter of a drainage systems is defined by topographic divides.Note: The continental divide of the U.S. the hydrologic divide between the Pacific and Atlantic drainage systems.
- Streams may act as either discharge or recharge divides depending on influent or effluent conditions. (See figure below)
ground water zones
- zone of aeration: The zone just below the surface where pores are filled with air but periodically saturated during storms. Water moves vertically down through the zone of aeration.
- zone of saturation: The zone of soil moisture where all pores are saturated.
|Water in the zone of aeration (vadose water) percolates vertically down until it reaches the water table. Water in the zone of saturation (phreatic water) follows the hydraulic gradient, flowing from areas of recharge to areas of discharge. Ground water will eventually resurface where it will flow into streams, the ocean, or seep from springs.|
The ground water contribution to a stream is called base flow, not to be confused with base level which is the elevation (sea level) below which a stream cannot erode.
The ground water table, the boundary between the zone of aeration and zone of saturation, fluctuates seasonally as rates of rechange and discharge vary. (Image modified from Earth Revealed, McGraw Hill)
Figure 2. The continuous cycling of water between the oceans, atmosphere and the land is referred to as the hydrologic cycle. The forces driving this cycle are thermal energy from the sun and gravity. (Modified from figure 16.l, Earth Revealed)
Permeability is the ability of a material to transmit water. The permeability of ground materials is controlled by the volume of void space, also known as porosity, the size of the pores, and their degree of interconnection.
The term stream refers to any channelized flow whether it is a gully, creek, or large river.
- Streams are the principal agent of erosion responsible for carving the landscape.
- Streams carry sediment to the ocean (baselevel) where it is deposited.
- Material is carried in streams as suspended load, bed load, and dissolved load.
- Stream provide an important habitat for wildlife
- Streams provide water for wildlife and man
- Agriculture proliferates on the fertile soils of river flood plains.
- Large rivers provide transportation and easy access to water thereby encouraging industrial development.
- Poor management and ignorance of streams can result in flooding and environmental damage (i.e. pollution, destruction of wetlands, etc.).
- Where a large river system is shared by more than one country political animosity can insue around the use and managment of the waters.
Conditions of stream flow
Downstream changes in flow
Based on contribution to ground water
effluent stream A stream that receives recharge(baseflow) from the ground water table because the water table intersects the stream channel.influent (loosing) stream: A stream that looses water to the ground because the water table lies below the channel.
Based on constancy of flow throughout the year
perennial: Perennial stream flow all year around, typically because the are effuent all year around.
- stable: Fluctuates little throughout the year
- flashy: Characterized by very high peak flows and very low low flows
intermittent: seasonally variable. May be effluent in the fall-spring and influent or dry during the summer.ephemeral: Flow only when it rains. Flutuates between influent and dry conditions.
Figure 3. Flow conditions relative to the ground water table. (Modified from figure 17.13, Earth Revealed.)
loosing stream: Discharge decreases downstream due to changes in climatic conditions or usage. Examples: The Nile and Colorado Rivers.
gaining stream: Most perennial stream flowing in the same climatic area.
Stream Channel Types
Ipswich River daily flows
Figure 3. Daily flows of the Ipswich River
This graph was created by plotting the mean daily flows of the Ipswich River for the period shown at the based of graph. (Data from USGS Water Resources) The baseflow, or amount of ground water contribution, to the river can be determined by drawing a line connecting points at the base of each peak. By doing so you can estimate the relative amount of runoff and ground water feeding a river. Note that ground water levels are typically greatest in the spring and decrease rapidly during the summer.
Figure 5. Unit hydrograph.
Over the last 40 years the drainage basin of a stream has be subject to widespread development. The diagram on the left is a unit hydrograph illustrating the response of the stream to storms of the same magnitude before and after urbanization.
Answer the following questions:
1. How does urbanization affect the volume and timing of peak runoff flows?
2. How is baseflow affected by urbanization?
3. Explain how urbanization of a drainage basin results in these changes in stream flow.
4. What are the adverse effects of such changes to aquatic life, industry and society?
Classification of zones based on degree of saturation
Classification of rock bodies or sediment layers based on permeability
Classification of aquifers based on the the presence of an overlying aquiclude that results in internal pressure
Rate of ground water flow
Nutrients (Fertilizers, Grease, Organic Matter)
Acids and Salts
Heavy Metals (Lead, Mercury, Zinc)
Toxic Chemicals (Pesticides, Organic, Inorganic Compounds)
Pathogens (Bacteria, Viruses)
Exercises and online quizzes
Case Study: Ipswich River
The Ipswich River has been placed on America River's most endangered rivers list. Not only is the Ipswich River a source of water for Salem it also feeds an important coastal estuary that is the breeding ground for shellfish, finfish and wildlife. List and discuss the stresses facing the Ipswich River. Discuss the factor causing the degradation of flow and water quality.Sources of information:
|Word Search: Surface Water Processes and Features|