The State Emergency Services is planning to send out another 3000 flood surveys to Griffith residents this week, after the originals were returned unopened.
Murrumbidgee Controller James McTavish says Australia Post is continuing to investigate the cause.
He says he is hoping Murrumbidgee Irrigation will reconsider responding to the survey after it refused to share flood data because of litigation fears.
Mr McTavish says he needs all key stakeholders to take part.
"It's really important that we get a broader picture," he said.
"Not just the information we're able to get from official sources, but you know, there are many, many private landholders and property owners throughout the MIA and along the river who have some unique information.
"And that unique information all goes to putting together the great big jigsaw puzzle of what actually happened.
"Particularly in this March event which was quite unusual."
Mr McTavish says he is hoping Murrumbidgee Irrigation will reconsider participating in the information gathering exercise.
"Without the full engagement of all of those different parts of the puzzle we get a less than perfect outcome," he said.
"It's really important that we are honest and share our stories and information.
"We just encourage people to participate fully."
Murrumbidgee Irrigation has continually refused ABC Riverina News offers to make its point of view about the March flood public, since Yenda landowners threatened class action.
© ABC 2012
13:39 EST With 28mm already recorded in the rain gauge this month, Alice Springs is having its wettest May since 2004.