Lecture 3 - Precipitation Analysis Flashcards
What does precipitation include?
rainfall, snowfall, hail, sleet
How does precipitation form?
by condensation of water vapour on condensation nuclei
What are the three storm types?
orographic, convective, cyclonic (frontal)
How does an orographic storm form?
front side of mountain is wet, wind goes up mountain and creates orographic precipitation, condensation goes over mountain onto drier back side of mountain
How do convective storms form?
warm moist air rises up due to its lower density, leads to more precipitation in the air which leads to clouds which leads to storms
How do cyclonic storms form?
idk
What are the 3 primary characteristics of rainfall events?
intensity, duration, frequency
Explain how rainfall events are treated statistically.
treated as random occurences, use probability theory to describe their likelihood of occurence which is typically presented in form of intensity-duration-frequency (IDF) curve
What is a design storm? What is the main difference between a design storm and a real storm?
need to develop a synthetic storm (temporal squence of rainfall amounts/intensities), real storm would have varying intensities of rainfall throughout its duration but design storm keeps it constant
Which type of NRCS Soil Conservation Service (SCS) is representative of Atlantic Canada?
III
What is the chicago storm distribution method used for?
designing urban stormwater system
What influences the selection of a design return period?
cost and safety
What is the Estimated Living Value?
largest magnitude possible for a hydrologic event at a given location, for example Probable Maximum Precipitation (PMP)
What is the design return period for an urban drainage system?
5 to 100 yr
What is the design return period for a highway culvert?
10 to 100 yr
What is the design return period for bridges?
50 to 100 yr
What is the design return period for floodplain mapping?
20 to 200 yr
What is the design return period for large dams?
estimated limiting value (PMP)
What happens as storm duration increases?
rainfall intensity decreses
What is the time of concentration of a catchment (Tc)?
travel time of a wave to move from the hydrualically most distant point to the catchment of the outlet
What happens if the storm duration is equal or greater than Tc?
whole watershed will be contributing flow to the outlet
How much does rainfall intensity increase for a 1 C increase in air temperature?
7%
What are the key snowpack characteristics?
depth, density, snowwater equivalent (SWE), ablation
How is snowfall and snowpack measured?
total precipitation gages, snowboards and ultrasonic sensors (depth measurement), snow stakes (depth), snowpack surveys (core samples for depth and SWE)
What is the Clausius-Caperyon (CC) Equation and Scaling Approach?
thermodynamic relationship that describes the relationship between temperature and moisture holding capacity
