Chapter 1 Hydrological Cycle

Definition: Hydrology is the study of water in the environment.
Hydrologic Cycle: Refers to the continuous circulation of earth’s water resources in solid, liquid, and vapor phases.
- Links the atmosphere, land, and oceans.
- Powered by solar energy.

Key Processes:
- Precipitation: Water falls to the earth in various forms (rain, snow).
- Evaporation: Water vaporizes from oceans and land surfaces.
- Infiltration: Water enters the ground, replenishing groundwater.
- Runoff: Water flows over land surfaces into streams and rivers.
- Transpiration: Water released from plants into the atmosphere.
Visual Representation (Fig. 1.1): Highlights the interconnections among precipitation, evaporation, infiltration, and runoff.

Groundwater Hydrodynamics:
- Water Table: The upper surface of groundwater.
- Groundwater Flow: Movement of water underground.
- Discharge and Recharge: How groundwater is replenished and discharged.
Statistics on Water Movement:
- Groundwater Discharge: 38
- Surface Discharge: 61
- Evaporation from land: 39
- Precipitation on ocean: 424

Transportation Components:
- Precipitation, Evaporation, Transpiration, Infiltration, Runoff.
Storage Components:
- Surface storage (e.g., ponds, lakes, reservoirs).
- Soil moisture storage.
- Groundwater storage.

Visual representation (Fig. 1.2): Shows how various components interact within the hydrologic cycle:
- Evapotranspiration, Stream Flow, Infiltration, Base Flow, Groundwater Flow.

Schematic Representation (Fig. 1.3): Describes the catchment of River A, highlighting key features such as:
- Watershed/Dive: The shared area where water flows into a river.
- Tributary Relationships: Streams flowing into River A.

Water Budget Principle:
- Equation: Mass inflow – Mass outflow = Change in mass storage.
- Example: P (Precipitation) - R (Runoff) - G (Groundwater) - E (Evaporation) - T (Transpiration) = ∆S (Change in Storage).
Detailed Breakdown:
- S = Total storage, including seasonal variations (Ss + Ssm + Sg).

Example Problem (Lake Water Budget):
- Calculation of water elevation change based on inflow and outflow statistics.
Second Problem (Catchment Rainfall):
- Calculate the amount of water unavailable for runoff due to infiltrations such as transpiration and evaporation.
- Discusses runoff coefficients and effects of afforestation on runoff.

Withdrawal Calculation:
- Estimation of constant withdrawal rate from a reservoir considering inflow, evaporation, and seepage losses.
- Important for managing water resources in the engineering field.

Breakdown of Water Resources:
- Data on various water bodies: oceans, groundwater, ice caps, lakes, rivers, wetlands, etc.
- Provides a percentage distribution of total water vs. freshwater.
Key Statistics:
- Oceans hold 96.5% of total water.
- Freshwater sources are very minimal compared to saline water, with ice caps and glaciers comprising a significant volume.

Engineering Applications of Hydrology:
- Irrigation: Ensuring agricultural water supply.
- Water Supply: Managing and distributing water resources.
- Flood Control: Mitigating flood risks through planning and structural interventions.
- Water Power: Utilizing hydrological resources for energy.
- Navigation: Maintaining waterway conditions for transportation.