Rainfall Data for New Orleans (finished)

[Dedpuhl]

Ok. I have almost given up. I have to do a hydrological study for a site in New Orleans for school. I have spent hours upon hours looking for the Intensity-duration-frequency curves for New Orleans, LA. I need this set of curves to determine a rainfall intensity...so I can determine storm runoff.

I know a lot of you are resourceful. I am hoping that my Anandtech family can help me. I am willing to offer a bounty for the information. I will have to think of a price and a way to pay later.

What I need:

-IDF or Intensity-Duration-Frequency curves for New Orleans, LA. It would be even better if curves were found for Kenner, LA.
-The information can also be found in numerical form (storm durations and intensities would be given)
-I have daily rainfall data for 60 years on Kenner and it is useless. I need rainfall intensities.


Any help would be greatly appreciated.

chris

 

[Dedpuhl]

I am offering a reward of $20 (USD) for the info.

 

[GTaudiophile]

Here's a start?

 

[etech]

eng.usf.edu/
To construct IDF Curves:
1. Fix duration, say 10 min
2. Collect all independent 10 min rainfall data
3. Rank them in order of decreasing depths
4. Compute recurrence interval:
n = no. years of record
m = rank - 1, 2, 3, 4,..., n
T = (n + 1)/m - Weiball Plotting Method

I'm not sure if that is what you are looking for or not. It's more of a "design storm" than actual but give it a quck read and see if it helps.

 

[Dedpuhl]

GT

That only gives averages of daily rainfall. I need intensities.


etech

I would need the data for the storms to use the model you have presented...

 

[Qacer]

Hey,

How about checking out this piece at your local library?

Author, etc.:
Hershfield, David M.

Title:
Rainfall frequency atlas of the United States : for durations from 30 minutes to 24 hours and return periods from 1 to 100 years / prepared by David M. Hershfield for Engineering Division, Soil Conservation Service, U.S. Dept. of Agriculture.

Published:
Washington, D.C. : Dept. of Commerce, Weather Bureau, 1963.

Description:
61 p. : ill., maps ; 35 x 53 cm.

Series note:
Technical paper / Weather Bureau ; no. 40

Series:
Technical paper (United States. Weather Bureau) ; no. 40.

Notes:
"May 1961, Repaginated and reprinted January 1963."
Includes bibliographical references.

 

[Dedpuhl]

<< Hey,

How about checking out this piece at your local library?

Author, etc.:
Hershfield, David M.

Title:
Rainfall frequency atlas of the United States : for durations from 30 minutes to 24 hours and return periods from 1 to 100 years / prepared by David M. Hershfield for Engineering Division, Soil Conservation Service, U.S. Dept. of Agriculture.

Published:
Washington, D.C. : Dept. of Commerce, Weather Bureau, 1963.

Description:
61 p. : ill., maps ; 35 x 53 cm.

Series note:
Technical paper / Weather Bureau ; no. 40

Series:
Technical paper (United States. Weather Bureau) ; no. 40.

Notes:
"May 1961, Repaginated and reprinted January 1963."
Includes bibliographical references. >>




The maps in that book show a different set of info. I saw those maps when I was going thru the NOAA website. I wish it was the stuff I needed. Thanks anyway...

 

[Dedpuhl]

I spent 4 hours looking for the info, and still couldn't find it. Guess I will have to fudge my numbers for now...

 

[guyver01]

How about THIS ?

 

[Dedpuhl]

<< How about THIS ? >>






I got excited for a second. That site just give average rainfall numbers...

 

[adinar]

Hey...as a practicing hydrologist...this question is right up my alley. My own hopes is that the information I give u is in time for you to complete your assignment.

If you can find a copy of the textbook _Applied Hydrology_ by Chow, Maidment, Mays (very standard hydrology textbook), just look up IDF curves in the index & you'll find a section dedicated to telling you how to compute them. In my copy of the book (c 1998), it's on pages 444-455).

If you don't have it, you'll have to get a copy of US Weather Bureau technical paper no. 40 (what we refer to as TP 40). Same one that was referred to earlier by Qacer that you said you saw. It contains maps of the US that shows rainfall depths for different durations and different return periods. The textbook actually has small copies of these maps within the pages I specified. Basically you can use these maps to compute rainfall intensities:

i = P / Td (where i=intensity, P=precip depth, Td=duration).

Of course you need several points to derive an intensity-duration-frequency curve.

From these maps, you can pick off preciptation depths for various durations (5min, 15min, 60min) and return periods (2yr, 100yr) for New Orleans or Kenner. Of course this won't give you all the data you need. To get the depths for durations (10min, 30min) & return periods (5yr, 10yr, 25yr, 50yr) that aren't specified by the maps, you have to interpolate.

To compute depths for 10 min duration given known depths for 5 min & 15 min duration for a given return period:
P10 = 0.41*P(5min) + 0.59P(15min)

To compute depths for 30 min duration given known depths for 15 min & 60 min duration for a given return period:
P30 = 0.51P(15min) + 0.49P(60min)

For return periods other than 2 or 100 years, use this equation:
PT = aP(2yr) + bP(100yr)

where coefficients a & b can be found below for a given return period:
T (return period) a b
5 0.674 0.278
10 0.496 0.449
25 0.293 0.669
50 0.146 0.835

So after interpolating, you should have a table of depths for various combinations of return periods & durations that looks somewhat like follows:

Duration Td (min)
Return period T (yrs) 5 10 15 30 60
2 # # etc
5
10
25
50
100

To get the actual intensity-duration-frequency curves, you'll need to compute the intensity for each depth value you have where i = P / Td (where i=intensity, P=ppt depth, Td=duration).

Now from these intensity points you can plot curves (one for each return period) with intensity on the vertical y-axis, and duration along the horizontal x-axis.

I hope that's enough to help you get started. Please let me know if I can be of any further assistance.

 

[jamison]

I am probably totally lost here, but worth a try. How about this?

 

[Shantanu]

Where's my $20?

 

[adinar]

<< I am probably totally lost here, but worth a try. How about this? >>



Hey...that helps a little bit too. That table actually summarizes depths for each return period at various durations (which I was trying to explain how to compute from the TP40 maps). From this webpage, you just need to divide the depths by the duration to get an intensity. However, the minimum duration is only 30 min - you may need smaller durations (5, 10, 15 min) to get intensities corresponding to those if you need 'em.

anyway, again, after computing the intensities, just plot the intensity (on the y-axis) vs the duration on the x-axis for each return period & you'll have your IDF curves..

Where's part of my $20?? hehe.

 

[Dedpuhl]

adinar and jamison have been the most helpful. I now have all the info I need. Thanks guys!