Introduction

Question 1

What is hydrology?

Answer 1

• Hydrology is a branch of scientific and engineering discipline that deals with the occurrence, distribution, movement, and properties of the waters of the earth.

Question 2

Why is hydrology important?

Answer 2

• Knowledge of hydrology is fundamental to water and environmental professionals (engineers, scientists and decision makers)
• in such tasks as the design and operation of water resources, wastewater treatment, irrigation, flood risk management, navigation, pollution control, hydropower, ecosystem modelling, etc.

Question 3

Describe the hydrological hydrological cycle?

Answer 3

• the hydrologic cycle, describes the continuous movement of water on, above and below the earth surface.
  1) The sun, which drives the water cycle, radiates solar energy on the oceans and land. Water evaporates as vapor into the air. Ice and snow can sublimate directly into water vapor. Evapotranspiration is water transpired from plants and evaporated from the soil.
  2) Rising air currents take the vapor up into the atmosphere where cooler temperatures cause it to condense into clouds. Air currents move clouds around the globe, cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as snow and can accumulate as ice caps and glaciers, which can store frozen water for thousands of years. Snowpacks can thaw and melt, and the melted water flows over land as snowmelt.
  3) Most precipitation falls back into the oceans or onto land, where the precipitation flows over the ground as surface runoff. A portion of runoff enters rivers in valleys in the landscape, with streamflow moving water towards the oceans. Runoff and groundwater are stored as freshwater in lakes. Not all runoff flows into rivers.
  4) Much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes aquifers, which store huge amounts of freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into surface-water bodies (and the ocean) as groundwater discharge. Some groundwater finds openings in the land surface and comes out as freshwater springs.
  5) Over time, the water returns to the ocean, where our main water cycle started

Question 4

What are the key processes of the hydrological cycle?

Answer 4

Precipitation :
Condensed water vapor that falls to the earth surface. Most precipitation occurs as rain, but also includes snow, hail, fog drip, sleet, etc.

Runoff:
The variety of ways by which water moves across the land. This includes both surface runoff and channel runoff. As it flows, the water may infiltrate into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.

Infiltration:
The flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.

Subsurface Flow:
The flow of water underground, in the vadose zone and aquifers. Subsurface water may return to the surface (e.g. as a spring or by being pumped) or eventually seep into the oceans. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures. Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years.

Evaporation and transpiration: The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere. The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration.

Question 5

What is the water balance equation?

Answer 5

The water balance equation for a catchment

P-R-G-ET=change in S

where  
P - precipitation, 
R - river runoff, 
G - groundwater runoff,
ET - evapotranspiration,   
S- storage change in a catchment.

Question 6

How is a catchment delineated?

Answer 6

Traditionally catchment boundaries have been manually derived from topographic maps, a labour intensive process.