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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

Hydrologic system

Terrestrial Water systems

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 ground water either re-emerges in streams and 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 in terrestrial basins and the ocean. Over 90% of all sediment entering the 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 lake, playa, or sea with no outlet.
Surface water

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.
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

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.
groundwater 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)

Hydrologic cycle


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)

The hydrologic responsible for: Components of the hydrologic cycle P=R+I+ET Factors determining the relative amounts of I, R, and ET: Flooding and the over all stability of stream flow relies not only on the amount of precipitation, but also on where the water goes once it reaches the ground. Drainage basins underlain by porous rock or sediment are less prone to flooding and their streams flow consistantly all year. Basins underlain by impermeable materials have high rates of runoff and streams are characterized by high peak flows and low low flows.


The term stream refers to any channelized flow whether it is a gully, creek, or large river.

  • Importance
    • 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.
  • Problems
    • 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

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.

stream conditions
Figure 3. Flow conditions relative to the ground water table. (Modified from figure 17.13, Earth Revealed.)
Downstream changes in flow
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

Drainage basin patterns Drainage Density (Dd=sum of L/Ad) Stream Discharge (flow)

Factors that influence flooding

Formation of and erosion by streams


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

Retrieving ground water


Types of pollutants Sources of pollution

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
Quiz questions

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