Review Session 1. Measuring Evapotranspiration Lysimeter – a large container holding soil and...
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- Slide 1
- Review Session 1
- Slide 2
- 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