R help - Mar 2014 - RCurl: How to select options in online form and download the data

Hi, 

I would like to download discharge data for thousands of rivers from this
website: http://ida.water.usgs.gov/ida/available_records.cfm?sn=12340000

I have managed to fill in the blank spaces in the form (start and end time)
using

library(RCurl)
url1<-"http://ida.water.usgs.gov/ida/available_records.cfm?sn=12340000"
start<-"1990-10-13"
end<-"2007-09-30"
result <- postForm(url1, fromdate=start, todate=end)

I get stuck on choosing an option on how to save the data in this piece of
the page source code:

<select name="rtype">
     <option value="1">Save to file</option>
     <option value="2">Save to compressed file</option>
     <option value="3">Display in browser</option>
</select> <input name="submit1" id="submit1"
type="submit" value="Retrieve
Data" />

I have three specific questions:

    How do I select option 1 or 3?

    How do I "click" the "Retrieve Data" button?

    How do I download the data?

I think that downloading the data might be more feasible with option 3
(display in browser).

    Option 1 (Save to file) will bring up the standard dialogue asking me
where on my computer to save the file. I don't know how to deal with this
dialogue in R. 

    Option 3 opens a new webpage with the URL:
"http://ida.water.usgs.gov/ida/available_records_process.cfm" (Note
the
river ID 12340000 is not in this URL). I could save the webpage as a .txt
file, but I don't know how to get to this webpage using R.

In either case the RCurl option followLocation would seem helpful, but I
cannot figure out how to tell R to save what is on the second webpage that
the first refers to. 

Any help will be much appreciated.

Frauke




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