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Hydrologic cycle with sketches and its need

Short answer

The hydrologic cycle is the continuous movement of water via evaporation, condensation, precipitation, and runoff, forming the framework for water balance. Its study is essential to quantify components for design floods, water availability, and sustainable planning.

Explain hydrologic cycle with neat sketches and justify its need in Engineering Hydrology.

Hydrologic cycle

The hydrologic cycle is the continuous movement of water between the ocean, atmosphere and land through evaporation, condensation, precipitation, runoff and infiltration. It is driven by solar energy and gravity.

   Sun's energy
      |
  Evaporation          Condensation -> Clouds
  + Transpiration  ^        |
      ^            |        v
 [Ocean]---------->|   Precipitation
      ^                     |
      |    Surface runoff   v
      +----- Rivers <--- [Land/Catchment]
      |                     |
      +--- Groundwater <----+  (infiltration,
           flow to sea          percolation)

Land-phase sketch of a catchment

        Precipitation (P)
   \ \ \ \ \ \ \ \
    Interception   Evapotranspiration
   -------------------------------------
    Depression storage | Surface runoff -> River
    Infiltration  \    |
   ~~~~~~~~~ Water table ~~~~~~~~~~~~~~~~
      Groundwater flow -> River / sea

Processes: evaporation, transpiration, condensation, precipitation, interception, infiltration, percolation, surface runoff, groundwater flow and snowmelt.

Need of the hydrologic cycle in engineering hydrology

  • It is the framework of hydrology: every topic (precipitation, losses, runoff, streamflow) is a part of the cycle.
  • The water balance of a basin (P−R−ET−G=ΔSP - R - ET - G = \Delta S) comes from the cycle and is used to find water availability.
  • Engineers estimate design floods, yield and droughts by quantifying the cycle components.
  • It shows how human activities (dams, deforestation, urbanisation, pumping) change evaporation, runoff and recharge.
  • It helps in planning water use for supply, irrigation and hydropower in a sustainable way.

✓ Answer checked by Claude Sonnet 5.5

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