Surface Runoff and Subsurface Drainage Flashcards
Parameter vs State: Parameter
porosity; capability
Parameter vs State: State
current %; right now
Factors that Greatly effect runoff
precip type, duration, total amount, intensity, temporal and spatial variations
Precipitation Type
rain, snow, hail
Duration of Event
1 day, 2 hours, 30 minutes (time)
Total Amount
0.2 in, 0.5 in, 2 in = 2.7 in
Intensity
4 in over 1 day or 6 hr?
Temporal Variations
fluctuation in ecosystem structure that effects rainfall
Spatial Variations
rainfall intensity differences over an area
IDF: Intensity
depth per time
IDF: Duration
time
IDF: Frequency
how common
100 year/1 hr event for JC (1961)
2.5”
PA IDF Characteristics
Appalachian Mountains and Lake Erie
Frequency Def
return period/probabilitiy
2 year Rain Event
will occur on average every 2 years; 50% chance of occurring in any given year; doesn’t mean it will occur every 2 years
Floodplain
flat area next to river/stream
Floodway
next to river; seasonal; floods more
Flood Fringe
extends from outer banks onwards
Riverfront Housing
need flood insurance & have to weigh odds of positives and negatives and chances
Probability and Forecasting
P = 1/T
P = probability & T = recurrence interval
Pt = (1-P)^r
given event will be equaled/exceeded at least 1 in next r-years
1-(1/T)
probability of not occuring
(1-(1/T))^n
probability of not occuring for n successive years
1-(1-(1/T))^n
probability of event at least once in n successive years; RISK
