Hydrology and Fluvial Geomorphology Key Terms Flashcards
Hydrological Cycle
The circulation of water through the atmosphere and across the Earth’s surface
Global Hydrological Cycle
The distribution of water as it moves either as a liquid, solid or vapour between the ocean, atmosphere and the land
Local Hydrological Cycle
The movement and distribution of water in a drainage basin
Porosity
The ability of rocks to store water
Precipitation
The fallout of water drops or frozen particles from the atmosphere
Precipitation intensity and type makes a big difference
Interception
Water that is caught / intercepted by vegetation
Water is stored temporarily until it is transpired or gravity moves it downwards by throughfall or stemflow
Interception rates can differ depending on the season (in winter there are less leaves so less water is intercepted)`
Throughfall
When water falls directly through the air to the ground
It is much faster than stemflow
Stemflow
The flow of water down the trunk or stem of a plant
The process that directs precipitation down plant branches and stems
Interception Loss
Evaporation from the surface of the leaf
Surface Storage
The part of precipitation retained at the ground surface
Includes temporary things such as puddles as well as larger things such as ponds and lakes
Infiltration
When surface water soaks down from the surface into the soil
The ground absorbs the water and prevents it from flowing into rivers (as surface runoff) which could cause flooding
Factors affecting Infiltration
Rainfall intensity and duration
Vegetation cover
Antecedent soil moisture
Evaporation rate
Slope angle
Degree of urban development
Soil composition / permeability
Soil Type affecting Infiltration
Clay has low levels of infiltration as it has limited pores which water can enter so it flood quickly
Loam and Sand are much more porous so they can hold more water so it doesn’t flood as easily or quickly
Overland Flow / Surface Runoff
The movement of water over the land due to gravity or a downslope to a body of water
It occurs when precipitation exceeds the infiltration capacity of the soil
They are very fast lateral flows
It is a key factor in causing flash flooding
Hortonian Overland Flow
Soil is not saturated but precipitation rate exceeds infiltration rate
Saturated Excess
Soil is already saturated and no more infiltration can occur
Throughflow
The movement of water laterally and downhill through the upper layers (more shallow and aerated) of the soil
The water travels through percolines which are natural gaps in the soil
It is faster and shallower
Groundwater Flow
Throughflow that occurs in the bottom section of the soil
It is slower and deeper
Groundwater Storage
Water stored in pores and spaces of underlying permeable and porous rocks
The phreatic zone concerns the layers of rock which are saturated.
This is dynamic and shifts over seasons and decades.
Baseflow
The portion of river’s discharge that comes from groundwater and throughflow only
Evapotranspiration
Evapotranspiration is the sum of evaporation and transpiration
It is an output
Both are affected by similar factors
Factors affecting Evapotranspiration
Temperature
Humidity
Wind speed
Light intensity
Vegetation type
Aquiclude
Stops percolation
Springs
The emergence of throughflow occurs at the surface due to impermeable layers of rock
The shallow underground throughflow force to the surface and becomes surface runoff
Leaves rocks as surface runoff
River Discharge
The volume of water moving in a river.
At its lowest point, a river will discharge into an ocean or sea
This is an output
Trellised Drainage Pattern
Trellised pattern develops in areas of alternating, weak and resistant bedrock
Rectangular Drainage Pattern
Rectangular pattern develops on highly jointed bedrock
Dendritic Drainage Pattern
Dendritic pattern develops on relatively uniform bedrock
Radial Drainage Pattern
Radial pattern develops on isolated volcanic cones or domes
Discharge
The movement of water in channels such as streams and rivers
Water Balance / Budget
When inputs and outputs are balanced, the system is said to be in a state of dynamic equilibrium
Soil Moisture Deficit
The degree to which soil moisture falls below field capacity.
In temperate areas, during late winter and early spring, soil moisture deficit is very low, due to high levels of precipitation and limited evapotranspiration
Soil Moisture Recharge
It occurs when precipitation exceeds potential evapotranspiration - there is some refilling of water in the dried-up pores of the soil
Soil Moisture Surplus
It is the period when soil is saturated and water cannot enter, and so flows over the surface
Soil Moisture Utilisation
It is the process by which water is drawn to the surface through capillary action
Percolation
When water moves slowly downwards from the soil into the bedrock
Aquifers
They are permeable rocks, such as sandstone and limestone, that contain significant quantities of water
The water in aquifers moves slowly so they act as natural regulators in Hydrological Cycle by absorbing rainfall that would otherwise enter streams and cause flooding
They also maintain stream flow during dry periods
River Regime Graph
Annual variation in the discharge of a river
Storm Hydrograph
Shows how the discharge of a river varies over a short period of time
Water Table
The uppermost layer of the phreatic zone is the water table
It separates the water-saturated ground and the unsaturated ground
