Intro to Hydrology Flashcards
Define Hydrology
The movement of water over, on and through the earth.
Describe the hydrological cycle
The hydrological (or water) cycle has no beginning or end. Water evaporates from the oceans, bodies of water, precipitation or from soil, or transpires from plants into the atmosphere. Hot air holds humidity and rises, until it cools in the atmosphere and condensation occurs. It then rains (precipitates) onto land or directly back into the ocean. Rain on land is either surface water runoff, into the nearest body of water. Shallow subsurface water makes its way to vegetation or a body of water within years. Deep groundwater percolation could take thousands of years to outflow into the ocean.
How is climate change impacting the water cycle?
Climate change intensifies the water cycle. As air temperatures increase, more water evaporates into the air. Wamer air can hold more water vapour (humidity), which can lead to more intense rainstorms. This can cause major problems such as extreme flooding due to high levels of runoff.
How is urbanisation impacting the water cycle?
Impervious surfaces associated with urbanisation alter the natural amount of water that takes each route through the water cycle. There is a decrease in the amount of water that percolates into the ground, resulting in an increase in volume and decrease in quality of surface water. This can lead to greater frequency and severity of flooding, channel erosion, and destruction of aquatic habitats.
Define a catchment or watershed
A hydrological area inside which precipitation and water flow is measured.
What is the water balance equation?
P = Q + ET + Ig ± ΔS
where:
P = Precipitation (mm)
Q = Discharge / runoff (mm)
ET = Evapotranspiration (mm)
Ig = Infiltration to groundwater discharge (mm)
ΔS = Change in storage (mm)
Why are water balance studies important?
They help us to understand the relative importance of components of the hydrological cycle within catchments.
For example, an impermeable clay covered catchment will have high surface runoff and low groundwater content. A permeable chalk surface will be the opposite.
What is the equation for the runoff coefficient?
C = Q/P
where:
C = runoff coefficient
Q = discharge/runoff
P = permeability
What areas would have a large value of runoff coefficient?
Areas with low infiltration and high runoff such as pavements and steep gradients.
What areas would have a small value of runoff coefficient?
Areas with high infiltration and low runoff such as forests or flat land.
What are the three basic precipitation processes?
Cyclonic or frontal precipitation, orographic precipitation and convective precipitation
Describe the process of cyclonic or frontal precipitation
A low-pressure system forms, usually due to the earth’s rotation and temperature differences.
Air moves toward the centre of this low-pressure system, bringing together warm, moist air from one direction and cooler, drier air from another.
The warm, moist air is lighter and rises above the cooler air, which sinks.
As the warm air rises, it cools. Its moisture condenses into water droplets or ice crystals, forming clouds.
When the water droplets grow large enough, they fall as rain, snow, or other forms of precipitation.
Describe the process of orographic precipitation
Moist air moves towards a mountain range or hill.
As the air reaches the mountain, it rises upward along the slope.
As the air rises, it cools down. The cooler air can’t hold as much moisture, so the water vapour condenses into clouds.
The condensed moisture falls as rain or snow on the windward side of the mountain (the side facing the wind).
After crossing the mountain, the air descends, warms up, and dries out, creating a drier region on the leeward side, known as a “rain shadow.”
Describe the process of convective precipitation
The sun warms the Earth’s surface, heating the air above it.
The warm air, being lighter, rises upward into the atmosphere.
As the warm air rises, it cools down. The moisture in the air condenses into tiny water droplets, forming clouds.
The rising air causes clouds to build up and become larger. When the water droplets in the clouds become large enough, they fall as rain.
What is a rainfall hyetograph?
A graphical representation of the distribution of rainfall intensity over time.
