water resources

water resources are sources of water that are potentially useful

coupled natural and human system

properties of H2O

to understand the hydrologic cycle and the processes operating with in it, we have to understand a number of important properties of H2O
these properties are all direct results of the capacity for H2O (in liquid or solid state) to form H bonds
oxygen more

the global water fluxes

most evaporation over ocean
most precipitation over land
can not calculate ground water flux

energy:the ability to do work

1 joule= work required to move 1m against 1N
many different forms, never destroyed

high specific heat

the heat (a form of energy) required to raise 1g of material 1 degree C
other material:
-dry soil, steel
as a result, water is a very good thermal buffer, requiring larger heat inputs to raise temperature than other natural or manufactured ma

high latent heat of vaporization

(Hv)=2440J/g (at 25 degrees C)
Hv= 2499-2.36T (T in C)
the heat required to move molecules from liquid to gas state (energy input needed for breaking H bonds and other intermolecular interactions, as well as to push back to the atmosphere
as a result, a g

high latent heat of condensation

(Hc)= -2440J/g (at 25 degrees C)
Hc= -(2499-2.36T) (T in C)
equivalent in magnitude to Hv, only represents heat that must be lost to condense H2O from gas phase to liquid phase

high latent heat of melting

(Hm)= 334J/g
heat input required for phase transition from solid to liquid (melt ice)

high latent heat of fusion

(Hf)= -334J/g
equivalent in magnitude to Hm, only represents heat that must be lost to form solid H2O (ice) from liquid

high surface tension

y=72.8mJ/m2 (at 20 C)
work required to create unit surface area
equivalent to work needed to break H bonds, and bring H2O molecules from interior of liquid water to surface


p=1.0g(cm-3) at 3.98C
defined as mass/unit volume
water density varies in unique way with temperature
max density at 3.98C, density of ice 0.9167
density change per C is greater at high temperatures

dissolving power

the universal solvent: dissolves more substances in greater quantities than any other liquid (in aggregate)


large absorption of radiant energy

light and water

the fate of light and reservoirs is important since it is a component of the energy balance and light is necessary to drive photosynthesis
we are thus particularly interested in the photosynthically available radiation or PAR
PAR overlaps with the visible


the process of water in the atmosphere returning to earths surface in liquid and solid forms
- rain, snow, sleet, hail

global scale precipitation

sun energy, air movement, ocean circulation, earths rotation, topography, vegetation feedback
earths energy budget
-solar energy input(up) reflection from clouds (down)
-heating air, land, and ocean (down)
-evaporation: main global precipitation source

global atmospheric circulation

driven by sun energy
steered by rotation of the earth, oceans/landmass/topography
1 degree global ocean circulation
-warm surface flow, cool subsurface flow

continental scale precipitation

transport of moisture through the northern pacific and NE atlantic and across the continent

regional scale orographic california

statewide average= 22.9inches or 582mm
rainshadow: windward side wet, leeward side dry
up in elevation: temperature decrease
-air cools up mountain=precipitation
-moisture budget then dry air left=rain shadow
-this is orographic effect

regional scale vegetation feedback

the amazon rainforest
moisture, lots of transpiration as source of moisture

mechanisms for precipitation

mechanism needed to cool the air to bring it to or near saturation
there exists a vertical temperature gradient in the atmosphere defined by the lapse rate
lapse rate: rate of change of temperature with elevation
-lapse rate varies with water content of a

at boiling point vapor pressure=atmospheric pressure


relative humidity (RH)

ratio of the amount of moisture in the air relative to the saturation vapor pressure

dewpoint temperature (Td)

the temperature (C) at which water vapor condenses into liquid water
for water to condense to liquid, the vapor must release heat of condensation= release of energy in gas phase
this heat is equivalent to that which must be added to evaporate water (laten

condensation nuclei are generally needed to promote condensation

NOx, soot, clays, sulfate, salts

sizes of aerosols and raindrops

condensation nuclei= 0.1-10um
cloud droplet: 20um
rain droplet: 2

droplets collide and increase in size

when they are falling their speeds exceed ascensional rate of air, precipitation falls and can reach terminal velocities of 6-10m/s


storage in winter
downstream supply in spring/summer
snowmelt achieves a similar result as a reservoir
-storage: release of water after the rainy season

measurement of precipitation

rainfalls into collection funnel
tipping bucket rain gauge

how do we measure snow

slower velocity due to complex shape with large surface, volume ration (1-2 m/s)
deposits on the landscape have widely varying density and water content

measurement of snow water equivalent

amount of water contained with in snow pack
fresh snow is often 8% density of liquid water, reaches 30-50% upon settling

snow pillow

4 stainless steel panels are plumbed together and filled with an antifreeze solution. weight of water in the snow forces the fluid to the pressure transducer which converts data to a signal for transmission
2015 water year was the driest on record for nev


the process of water in the atmosphere returning to the earths surface in liquid and solid forms
spatial distribution of precipitation is controlled by processes ultimately driven by the suns energy and the physical/chemical/biological characteristics of


phase change in which liquid water is converted to vapor
evaporation requires a large energy input (2.4KJ/g) to break H bonds of water in liquid phase and move to gas phase
as we have seen, the theoretical amount of water vapor in the air (Psat) increases

rate of evaporation

function of:
-vapor pressure gradient between air phase and H2O at the surface
-wind speed and energy budget
estimating lake evaporation rate
-pan method
.direction measurement of loss of water depth from pan: Ep(cm/d)

energy budget

recall that sun energy warms the lake surface (where the evaporative action takes place) and some also penetrates the lake, increasing the energy storage in the lake water
this stored energy also effects E
things get complicated as energy storage in the l

heat loss

heat loss due to evaporation is 1 of 5 processes that regulate the net flux heat Jnet of water resources (oceans,lakes)
loss of heat due to evaporation lowers the amount of heat and therefore temperature of a volume of water

lake elsinore

sublimation and evaporation of ice and snow
latent heat of sublimation= latent heat of melting and latent heat of vaporization
mass balance at the lake/atmosphere interface
-turbulent transfer of water vapor from evaporating surface to atmosphere
-based o

efforts to reduce lake/reservoir evaporation

monolayers/surface films
-cetyl or stearyl alcohol reduce evaporation by 5-40%, less effective at large scale
solid covers and shades
-plastic balls and sheets, reduce evaporation up to 90%, now longterm use on LA municipal reservoirs


evaporation from plant surfaces into the atmosphere
one of the principle mechanisms by which precipitation falling on land is returned to atmosphere
accounts for 10% of total moisture in the atmosphere
since difficult to separate true evaporation from tra

factors affecting transpiration

temperature, relative humidity, wind and air movement, soil moisture availability, light supply, and type of plant (number of leaves, number of stomata, presence of cuticle)
transpiration serves 3 essential roles
-movement of minerals up to root (in xylem

what happens after you burn a watershed

evapotranspiration decreases extemely


a portion of the precipitation falling on a watershed generally passes through the watershed as streamflow
a record of streamflow over time is referred to as a hydrograph
features include: baseflow, direct runoff, rising limb, falling limb, base time, and

components of streamflow

baseflow: is the relatively steady flow that results from ground water inputs into the stream
direct runoff: contributes to the flow from rainfall or snowmelt event that could reach the stream via overland flow or interflow
rising limb: increase in stream

watershed characteristics

watershed characteristics also influence shape of hydrograph
a steep sided watershed results in a short lag time and rapid (flashy) response to rainfall event
a flatter watershed yields a longer lag time and slower response
beyond steepness and shape of w

discharge (flow rate, Q) measurement

stream discharge is the rate at which volume of water passes through cross-section per unit time
-english: cubic feet per second
-SI: cubic meters per second
both direct and indirect methods are commonly used to measure streamflow

direct measurements

volumetric measurement (bucket method)
-for small flows (e.g. springs) and involves measuring time to fill a container of known volume
velocity area method
-requires measurement of cross sectional area of stream and average stream velocity
-stream velocit

indirect methods

stage-discharge relationships
-stage discharge relationships (rating curves): empirically developed relationships based on a large number of simultaneous discharge and stream depth
-rating curve, rating equation, rating table
slope area method

fluvial geomorphology

the study of river form and structure

river reach

streams and rivers usually have alternating sections or segments (reaches) of vary velocity, depth and streambed composition
riffles: shallow, with flow velocity sufficient enough to keep bottom of silt and debris
pools: deeper, with lower velocity and fi

vegetation factors affection interception

type of vegetation (trees, shrubs, grasses, or litter)
deciduous or evergreen (D holds more in the summer, E holds more in the winter)
canopy density (higher density=greater interception)
tree spacing (as spacing increases, interception and stemflow decre

atmospheric factors affecting interception

form of precipitation
state of leaf due to temperature
day vs night rain
drying between precipitation events
storm characteristics (intensity, duration, frequency)
wind (dislodges interception and turns it into throughfall)
-forest edge effects are

direct runoff

represents third major process in hydrologic cycle
can be generated by surface and subsurface mechanisms
-overland flow-surface runoff that occurs when the rate of precipitation exceeds in filtration of H2O into soil
-subsurface storm flow (interflow): wa

not all precipitation that falls on a watershed ultimately results in runoff and flow within a stream or channel

watershed catchment: area above a point on stream from which water drains to the stream
interception: precipitation retained on vegetal surfaces and evaporated back to atmosphere (interception storage)
depression storage: water that is stored in surface p


process in which H2O enters into a soil profile form the surface boundary and occurs as a result of
-gravity and capillary action
infiltration rate is a function of soil properties
-total porosity, pore size distribution, chemical and surface properties,

hortonian overland flow (infiltration excess overland flow)

rainfall intensity and infiltration rate dependent
-also must fill depression storage

saturation excess overland flow (dunne overland flow)

rainfall intensity and infiltration rate dependent
direct precipitation on saturated areas
return flow
-when interflow enters a saturated rate above the rate of interflow exiting the area

soil and soil water relations

soil is typically a 3 phase system comprised of solid, liquid (H2O), and air
water that has infiltrated into the soil then becomes a part of the soil moisture and occupies available pore space and or displaces antecedent water
-gravitational H2O: is held

soil moisture potential (matric potential)

related to these capillary forces and defines the energy state of H2O in soil, essentially the amount of negative pressure (suction) to pull H2O out of soil