Measuring Evapotranspiration Lysimeter a large container
holding soil and plants. Mass Balance: Debate: Pros/Cons
Slide 3
Events during Precipitation - Infiltration Not all water that
falls will reach the water table Infiltration Capacity is measure
of a soils capacity to absorb water Highly variable soil type, but
also the same soil varies depending on current moisture content
Horton Infiltration Capacity Equation
Slide 4
Streams and Groundwater Gaining vs Losing How do you determine
which it is? Groups
Slide 5
Stream Hydrographs Baseflow Recessions Baseflow is is the
portion of streamflow that comes from subsurface flowstreamflow
Baseflow recession in a stream occurs when groundwater feed to a
stream decreases
Slide 6
Stream Hydrographs Baseflow Recessions Complex thing that
depends on lots of characteristics in a watershed (topography,
drainage, soils +geology) but often the equation is simple
Slide 7
Determining Ground-Water Recharge from Baseflow Seasonal
Recession Method (a) Find time t 1 when Q=Q 0 /10 (b) Find V tp,
the volume of potential gw discharge (c) Calculate potential
baseflow at t, the end of the recession (d) Recharge= V tp (next
season)- V t (season 1) Apply algorithm to this figure
Slide 8
Determining Ground-Water Recharge from Baseflow Recession Curve
Displacement (a) Find t 1 (b) Compute t c =0.2144t 1 (c) Locate
time t c after peak (d) Extrapolate recession A and B to find Q A
and Q B at t c (e) Apply equation
Slide 9
Open Channel Flow Manning Equation Imperial Units V (ft/s)
average velocity R (ft)- hydraulic radius (ratio of cross area to
wetted perimeter) S (ft/ft) - energy gradient n Manning roughness
coefficient Metric Units V (m/s) average velocity R (m)- hydraulic
radius (ratio of cross area to wetted perimeter) S (m/m) - energy
gradient n Manning roughness coefficient a b
Slide 10
Manning Roughness Coefficient Stream Typen Mountain stream with
rocky bed0.04-0.05 Winding Natural Stream with weeds 0.035 Natural
stream with little vegetation 0.025 Straight, unlined earth
channel0.02 Smoothed concrete0.01 Entirely empirical so be very
careful with units!!!
Slide 11
Useful Definitions Confining Layer geologic unit with little or
no intrinsic permeability Aquifuge Absolutely impermeable unit that
will not transfer water Aquitard a layer of low permeability that
can store ground water and transmit it slowly from one aquifer to
another Unconfined/Confined Aquifer an aquifer without/with a
confining layer on top. Leaky Confined Aquifer a confined aquifer
with an aquitard as one of its boundaries Perched Aquifer a layer
of saturated water that forms due to accumulation above an
impermeable lens (e.g. clay) Water Table depth where the soil
becomes completely saturated
Slide 12
Porosity Porosity is the ratio of the volume of voids to the
total volume 0
