Harvesting Water
Rainwater Run off
Geology, Ground water, India
Ground water Recharge
Rainwater Harvesting methods
Contact

Where did water come from?
It appears to have been bound up in the silica-based materials such as micas and amphiboles which accreted to form the Earth. The heat released during this process would have been sufficient to drive off this water, which amounted to about 0.01% by mass of the primordial material. The hydrologic cycle refers to the steady state that exists between evaporation, condensation, percolation, runoff, and circulation of water. The cycle is driven by solar energy, mainly through direct vaporization, but also by convective motion induced by uneven heating.
Run off Generation

Various process and pathways determine how much and how fast precipitation becomes streamflow.

•      Factors effecting runoff response:

•      Precipitation form, intensity, duration, distribution

•      Storage (soil moisture, saturated areas)

•      Flow pathway (e.g., shallow soil layer vs. deeper soil layer, or overland surfaces or subsurface)

•      Spatial distribution and occurrence of geomorphic features (e.g., deep alluvial valley bottoms, degree of convergence, etc.)

The Water Cycle: Surface Runoff

Surface runoff is precipitation runoff over the landscape. Rain begins to flow overland downhill on hitting saturated/ impervious ground it. Meteorological factors affecting runoff:
  • Type of precipitation (rain, snow, etc.)
  • Rainfall intensity
  • Rainfall amount
  • Rainfall duration
  • Distribution of rainfall over the drainage basin
  • Direction of storm movement
  • Precipitation that occurred earlier and resulting soil moisture
 Other meteorological and climatic conditions that affect evapo-transpiration, such as
  • temperature, wind, relative humidity, and season
  • Physical characteristics affecting runoff:
  • Land use
  • Vegetation
  • Soil type
  • Drainage area
  • Basin shape
  • Elevation
  • Topography,
  • Drainage network patterns
  • Ponds, lakes, reservoirs, sinks, etc.
  • Human activities can affect runoff
Run off Processes

Channel Interception

•      1% or less in saturated/wet/channel area

•      Initial rise in hydrograph is often associated with channel interception

•      Small sediment “pulse” as channel is washed by intercepting precipitation

 

Overland flow (i.e., infiltration-excess overland flow, Hortonian overland flow)

•      Excess precipitation that could not infiltrate

•      Compacted surfaces, roads

•      Sharp hydrograph spike

•      Diminished water quality, especially in urban areas
Groundwater flows
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Interflow

Many processes are considered interflow

One of the largest components in forested watersheds

•      “Old” water concept (typically >50%, usually ~70% old water)

•      Groundwater

•      Slow or no response

•      “Baseflow” or “dry-weather” flow in stream

 

Groundwater flows

Groundwater  is hydraulically connected with surface water; allowing streams to flow even during periods of extended drought.  The top surface of the groundwater, called the water table, may fluctuate depending upon topography (it rises and falls with the terrain), recharge (heavy rainfall may temporarily elevate the water table) or drawdown (lowering of the water table may occur through groundwater withdrawal via well pumping). Groundwater does not move in the way that surface water does because the path is not smooth - groundwater must wind a very slow, twisting path between void spaces in porous rock or unconsolidated sediment.  However, groundwater may not always be retrieved from water-bearing rocks or sediments; it is not enough for a rock to contain void spaces (porous); the pore spaces must be interconnected.

Rock formations containing extractable ground water are known as aquifers.  Rocks that are rich in clay minerals (such as shales) "bind up" water through adsorption, such that the water is not extractable, and are classified as aquitards.  An extreme example of an aquitard is called an aquiclude.  Aquicludes are often used to locate hazardous waste landfills because they provide a natural barrier to leaking waste containers.

 The rate of groundwater flow through a rock formation is called the permeability. Aquifers have relatively high permeability, which aquitards have low permeability.  Aquicludes have extremely low permeability.

Aquicludes may act as a confining layer preventing the downward movement of groundwater, and sometimes creating a locally elevated or perched water table.  If the perched water table outcrops at the surface (note in the diagram below  the left edge of the perched water table ends at the slope of the hill), groundwater may form a spring or a seep.
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Groundwater is the collective water that exists in porous rock formations and/or unconsolidated sediments, such that this water fills in the void spaces in what is known as the saturated zone.  The top surface of the groundwater is called the water table or piezometric surface of the saturated zone.  Above the water table, the rock formations through which rain water may percolate downwards to recharge the water table is known as the unsaturated zone, or the zone of aeration.   There is collectively more groundwater than all surface water sources combined.  In land-locked areas, groundwater is the main source of freshwater and is usually extracted by drilling wells.
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