Raifall events

[slam00000]

I want to test my slope model sensitivity to a hypothetical extreme rainfall event.
Is an extreme precipitation event represented by a daily rain amount of 50 mm over 3 consecutive days realistic in Canada and /or the US regions.

Please refer me to a refernce (if possible). Environment Canada website is not explicit enough about this matter.
Also, I could not get what I want from reading several articles in the Climte journals . I have spent the whole day trying to officially find a source justifying my above extreme event assumption which I made just for academic purpose. Thanks for your help

 

[RWF7437]

Sorry, I do not have data for Canada.

In the U.S. one source for extreme rainfall events may be found at the USGS website, using the National Flood Frequency program (NFF). There you will find extreme rainfall amounts based on work by Crippen & Bue.

Also, for the U.S. try googling it.

good luck

 

[hokie66]

It depends on where you are, but I don't think 150 mm in 3 days is an extreme rainfall event in many places.

 

[BigH]

I think I remember Bombay having some 36 inches of rain in one day a few years back . . . mmm -

 

[jdonville]

If I recall correctly the standard extreme rainfall design event is based on precipitation records from hurricane Hazel back in the '60s - one of the few hurricanes to actually make it to Canada.

Hope this helps.

Jeff

 

[DMcGrath]

Perhaps also to consider is how much of the rainfall infiltrates into the soil vs. direct runoff. The common hydrology models assume a portion of the rain event saturates or is otherwise detained by the soil, then the remainder runs off. If this is for a slope stability and you are considering saturation, then the infiltration amount would be of interest. For surface slopes, the runoff amount would be the value you want. The fractions of infiltration and direct runoff would be a function of soil types (clay vs. sand for instance), vegetative cover, slope, etc.

 

[slam00000]

Hello all
Dear DMcGrath
I need the infilitration as I want to examine how far the phreatic surface level will be influenced by the rainfull event so if the extreme rainfall event is 100 mm/day I am applying it fully as a flow on the surface of the slop neglecting the evaboration oth the influence of the other near surface conditions. Please guide

 

[DMcGrath]

Calculating infiltration is a subject of many methods and research (Google "Green Ampt"). If you simplify it somewhat and consider that "what does not run off will infiltrate", then you can use most any hydraulic method and concentrate on the non-runoff fraction of the precipitation.

In a nutshell, heavy, clay soils will have more runoff (less infiltration) and sandy soils will have less runoff and more infiltration. Ground cover (vegetation or bare soil) and slope also influence infiltration. For some background reference, start with the TR-55 method, read Chapter 2.

http://www.info.usda.gov/CED/ftp/CED/tr55.pdf

The TR-55 method calculates what is called the "initial abstraction" which is the first bit of a rain event that does not run off (your infiltration). The Ia is based on the characteristics of the soil (modeled as the curve number (CN)).

This is a bit simplistic, but you can decide how much detail for the infiltration you need.