use warnings;
use strict;
## Select input and output files
my $input_file  = 'InputFile.OH1';
my $output_file = 'OutputFile.csv';
open my $ifh, "<", $input_file
   or die "cannot open '$input_file' for reading: $!\n";
open my $ofh, ">", $output_file
   or die "cannot open '$output_file' for writing: $!\n";

## Creates a header at the beginning of the file
my $header = "HEC1_ID,Q100_Base,TTP,Area\n";
print $ofh $header;

## Extracts data from input and sends through STDOUT to output file
select $ofh;
while (<$ifh>) {
 s{
  ^             # at the beginning of the line
  \+            # followed by literal plus
  (?:\s+(\S+))  # column one
  (?:\s+(\S+))  # column two
  (?:\s+(\S+))  # column three
  (?:\s+\S+){3} # skip three columns
  \s+(\S+)$     # catch the last one, too
 }{$1,$2,$3,$4}x
  and print;
}
select STDOUT;