Water Resources II

8/11/2019 Water Resources II

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RUN OFF

The term runoff is used for water that is on the runor in a flowing state in contrast to the waterheld in depression and water stored in theatmosphere. The runoff expressed as cm of

water over a catchment ar the total water incubic-metre or hecatre-metre for givencatchment.

Runoff is broadly classified into three types

a) Surface runoff b) Sub-surface runoff c) Base

flow

Rain disposed off in the following manner a) Basinrecharge b) Direct runoff c) percolation downto groundwater d) Evaporation and

transpiration


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FACTORS AFFECTING RUNOFF

1. Precipitation characteristics

2. Shape and size of the catchment

3. Topography

4. Geological characteristics

5. Meterological characteristics

6. Character of the catchment surface

7. Storage characteristics


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Groundwater

Groundwater is water, which originates from the infiltration of fluids through thesoil profile and accumulates below the earth's surface in a porous layer.

Porosityis the percentage of open void space in the subsurface material. It isexpressed as a percent.

Permeabilityis how readily a fluid can flow through a material. Often referred toas "connected pore space". The property of porous material which permit thepassage of water through interconnecting voids.\

Transmissibility:

Pieziometric surfaceis the surface in which water is pushed up to by thepressure below.

Springis where water flows out without the aid of pumping. It may be caused by

hydrostatic pressure (pressure pushing upward), or the intersection of thepieziometric surface with the ground surface. Also referred to as anArtesianSystem.


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An aquifer may be defined as formation that contains sufficientsaturated permeable material to yield significant quantities ofwater to wells and springs. This implies an ability to store andto transmit water E.g Unconsolidated sand and gravels .

Aquiclude A saturated but relatively impermeable material thatdoes not yield appreciable quantities of water to wells E.gClay.

Aquifuge : A relatively impermeable formation neither containingnor transmitting water E.g. Solid granite.

Aquitard : A saturated but poorly permeable that does not yieldwater freely to wells but transmit appreciable water to orfrom adjacent aquifers.


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Flowing or Artesian Well Development


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Anaquicludeis a unit of rock or layer of rock, which is impermeable to fluids. It acts as abarrier to fluid flow. There probably are no true aquicludes.

There are two (2) scenarios that may occur with aquifers:

1. Confined Aquifer -- when an aquifer is bounded by two (2) aquitards (one above andone below)

2. Unconfined Aquifer -- when an aquifer is not bounded on the surface side by anaquitard so that fluids may flow freely above the aquifer.

The distribution of groundwater is present in several distinct layers or zones:a. Soil moisture zone -- usually top soil; much infiltration; much organic materialb. Zone of aeration (Vadose Zone) -- mostly air but some interstitial water

c. Capillary fringe -- transition between unsaturated and saturated zone; top of aquiferd. Zone of saturation (Phreatic Zone) -- pores completely saturated with water; mainaquifer storage zone

Where does water in the ground originate?Hydrologic Cycleexplains the origin of groundwater.Depicts the occurrence and movement of water in the earth-atmosphere system.Water enters the GW system atrecharge areas.Water leaves GW system atdischarge areas.


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Occurrence of water1. 97% of all water on earth is in oceans.

2. ~ 2% of the earth's water in ice caps & glaciers3. About 0.6% of earth's water is groundwater

Water in rivers, lakes, and the atmosphere amounts to less than0.02% of earth's water

Movement of WaterAtmosphere to surface: precipitationSurface to atmosphere: evaporation -- liquid to vaporSublimation -- solid to vaporTranspiration -- release of water vapor by plantsOn surface: downslope movement to lakes, streams, and oceansBelow surface: movement of groundwater

If GW seeps into stream, stream is againing stream.If water seeps from stream into subsurface, it is alosing stream.


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Precipitation

Runoff

Precipitation

Evaporation

Infiltration

Hydrologic Cycle


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In areas in which soluble rock (i.e., limestone) is present in the layer near thegroundwater, a situation often develops that is characterized by rock layerdissolving. This is referred to askarst topography.

Indiana, Kentucky, and Georgia are areas in which karst topography may develop.

The area is characterized by: a. Soluble bedrock near the surface b. Disappearing streams that feed downward with no end on the surface c. Sinkholes d. Patchy, pockmarked surface topography e. Frequent fluctuations in water table f. Caves g. Submerged caves

Caves are formed by the dissolving nature of the rock fed by groundwater. Large

cavities develop as well as solid drops of rock that precipitate from thegroundwater solution.Those overhead are called stalactites (stick tight to the ceiling) and those that

build up from the ground floor are termed stalagmites (with a ''g'').


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There are several problems, which can develop, associated with the lowering ofthe groundwater surface due to overuse/over pumping:

1. Cone of depression develops 2. Lowering of the pieziometric surface, thus wells dry up 3. Saltwater incursion/intrusion if near an ocean

Groundwater ContaminationContamination results in a decline in water quality.

Common contaminants:Types SourcesNitrates Sewage, Fertilizers, FeedlotsPesticides, herbicides Agriculture, lawn careOrganic chemicals Industrial wastes, landfills, spills/leaks of fuelsMetals Industrial processesBrines Oil production

Protecting groundwater resources Apply agricultural chemicals properly Build better landfills Regulate disposal of hazardous materials Regulate underground storage tanks (USTs)

Limit contaminant levels in drinking water supplies.


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Cone of Depression Development


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Development of Contamination in Groundwater


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Charbeneau, 2000.

porosity


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Figure 15.1


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Water Resources II

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