HYDROLOGIC PROCESSES
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GEOG 3B
Land, Water & Life
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Hydrologic cycle
Mass balance equations
Flows & reservoirs
Application
Summer 2008
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HYDROLOGIC CYCLE
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GEOG 3B
Land, Water & Life
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Hydrologic cycle:
Hydrology is the study of the movement, distribution, and quality of water
throughout the earth; the hydrologic cycle describes the continuous
movement of water above, on, and below the surface of the Earth.
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We may identify various components of the hydrologic
cycle, including:
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Summer 2008
Atmospheric Component
Vegetation Component
Surface Component
Soil Component
Groundwater Component
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HYDROLOGIC CYCLE
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GEOG 3B
Land, Water & Life
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The hydrologic cycle is a closed system
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Water is essentially neither created nor destroyed as it flows through
various environments near the Earth's surface
Small amount of water is lost to space
Small amounts of water are lost/gained from chemical reactions
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Each component of the HC contains:
Reservoirs [ ΔS ]
Flows [ Inputs & outputs ]
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We can write Mass Balance Equations to represent the Flows of Water.
Consider water flowing into and out of any arbitrarily chosen volume
near to the Earth Surface. It will always be true that:
INPUT - OUTPUT = CHANGE IN STORAGE
( I - O
=
ΔS )
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MASS BALANCE EQUATIONS
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MASS BALANCE EQUATIONS
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GEOG 3B
Land, Water & Life

We can represent the hydrologic Mass Balance of
Water at different spatio-temporal scales:
Micro Scale (meters)
Macro Scale (kilometers)
Global Scale
Balance:
Summer 2008
Precip = Evap + GrndwtrFlo + Runoff
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FLOWS & RESERVOIRS
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ATMOSPHERIC COMPONENT
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GEOG 3B
Land, Water & Life
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Flows and Reservoirs of the Atmospheric Component:
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Input: Evapo-transpiration
Output: Precipitation
Storage: Air
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At global scale:
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Precipitation approximately 39in/year
1in water held in Atmosphere
Precipitation varies by Climatic Zones
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At regional scale
Variation in Precipitation by Landform/Elevation
Inverse relation of Precipitation Intensity and Duration
Summer 2008
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VEGETATIVE COMPONENT
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GEOG 3B
Land, Water & Life
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Main flows and reservoirs of the vegetation component
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Input: Precipitation, plant roots
Output: Stemflow, transpiration
Storage: Roots, leaves, stems, etc.
Approximately 10-29% Precipitation is intercepted or evaporates
Interception generally declines sharply over time during Precipitation Event
Summer 2008
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LANDSURFACE COMPONENT
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GEOG 3B
Land, Water & Life
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Main flows and reservoirs of the surface component
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Input: Precipitation, stemflow, surface runoff, soil/groundwater outflow
Output: (Soil) infiltration, runoff, evapotranspiration
Storage: Surface depressions, rivers, lakes
Evaporation rates approximately 15” /year in NE USA
to 90” /year in SW USA
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Mean daily solar radiation
Mean annual lake evaporation
Mean annual ET
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LANDSURFACE COMPONENT
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GEOG 3B
Land, Water & Life
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Surface runoff is one of the most processes in terms of
the evolution of landforms
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Surface runoff is:
Water remaining from rainfall after evapotranspiration and Infiltration
Augmented by Water flowing from Soils and Aquifers
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Surface runoff takes two major forms:
Overland Flow
Streamflow
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Streamflow may be characterized in terms of:
The stream hydrograph which represents the variations of Stream Discharge
over time (at a given location)
Various flows, such baseflow and flood flow
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SOIL WATER COMPONENT
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GEOG 3B
Land, Water & Life
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Main flows and reservoirs of the soil component:
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Input: Infiltration from surface, soil/groundwater Inflow
Output: Evapotranspiration, soil/groundwater outflow
Storage: Soil particles, porespaces
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Soil Water occurs in three forms
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Hygroscopic Water
Capillary Water (up to the Field Capacity of a Soil)
Gravitational Water
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Summer 2008
Infiltration is a key process that determines how much surface runoff
occurs in a given rainfall event
Infiltration capacity represents the rate at which soil can absorb rainfall
under various rainfall rates
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SOIL WATER COMPONENT
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GEOG 3B
Land, Water & Life
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Capillary water
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Summer 2008
Force underlying capillary water results from attraction to surfaces/water
molecules pressures of 0.3-32 bars
Field capacity is the maximum amount of capillary water that can be
held in a soil and is related to particle size
Capillary flow from high to low moisture content maximum transport in
medium sized particles
Height travelled by capillary water determined by balance of
gravity/molecular forces
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SOIL WATER COMPONENT
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Soil infiltration:
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GEOG 3B
Land, Water & Life
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The rate at which water infiltrates into a soil determines how much
surface runoff, and hence erosion, can occur
The rate of infiltration of a soil under given rainfall conditions is
represented by the concept infiltration capacity
Infiltration capacity is determined by the various soil properties, such as
texture
Other concepts:
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Summer 2008
Soil-water budget
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GROUNDWATER COMPONENT
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GEOG 3B
Land, Water & Life
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Main flows and reservoirs of the groundwater component
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Summer 2008
Input: Soil/groundwater inflow
Output: Evapotranspiration, soil/groundwater outflow, runoff
Storage: Pore spaces, fissures, ...
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GROUNDWATER COMPONENT
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GEOG 3B
Land, Water & Life
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Aquifers
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Rocks that hold groundwater are called aquifers
Most water enters an aquifer from soils at the surface
Their upper unsaturated portion is called the Vadose Zone
They are typically charactized by:
A Water Table, which is the level at which the rocks are saturated with water
Groundwater Flow
Summer 2008
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GROUNDWATER COMPONENT
GEOG 3B
Land, Water & Life
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The amount of Groundwater that may be held in an Aquifer depends on the
porosity of the rock
The flow of water through an aquifer (groundwater flow) is determined in
part by the permeability of the rock
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There are two main classes of Aquifer depending on on
the configuration of Permeable and Impermeable Rock
Layers
Unconfined Aquifer
Confined Aquifer
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GROUNDWATER COMPONENT
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GEOG 3B
Land, Water & Life
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The flow of water in an Aquifer can be approximately
described by Darcy's Law:
Q = A* K [Δ h/ Δ x]
where:
K is hydraulic conductivity
Δ h is drop in Head
Δ x is distance of flow
A is Area of flow
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GROUNDWATER COMPONENT
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GEOG 3B
Land, Water & Life
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Other concepts:
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Summer 2008
Transmissibility
Springs
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APPLICATION OF HYDROLOGY
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GEOG 3B
Land, Water & Life
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Flood forecasting / watershed management
Groundwater availability / management
Saltwater intrusions
Pollution / remediation
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NTS PROJECT – SAN DIEGO CREEK WATERSHED
Orange
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San Diego
Creek
Watershed
Boundary
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Pe
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C
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n
W
Creek
Sa
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o
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eg
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eg
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San D
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Di
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h
Project Sites
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Upper
Newport
Bay
as
C
re
ek
Lake Forest
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Newport Beach
Type 1- Offline Water Quality Wetlands
Type 2 - Inline Water Quality Wetlands
N
0
2
4 Miles
Type 3 - Water Quality Wetlands within Existing or
Proposed Detention Basin
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