Do they have anything to climb? They appear to be lying on the soil. That would encourage rot.

No, because I stupidly believed people who said densely planted, short growing peas were self supporting.

I grow short peas and every year I stick cuttings from the butterfly bushes in for them to climb on. Brits call them "pea sticks" and they're quick to install and quick to take down.

If they are turning dark at or near the soil line or near where they are in direct contact with the soil then it is the disease 'damp-off'. Search will pull up many discussions about it.

But if they are snapping like small sticks then it is a stem turgor (rigidity) issue because the stem cortex cells are over-filled with water.

"Densely" planted means different things to different folks and it can work when done properly. But that doesn't mean even the most dense planting can hold up to heavy downpours.

Dave

Would damping off occur in mature, blooming plants?

Probably so with these recent drowning rains and the plants are compacted and piled on top of themselves. Peas will stand alone, if there is no wind above 5 mph for 2 months.

Quite the peackle you're in!

Would drying out the area, perhaps by using a fan, help?That might give them enough strength to be staked up?

Edit: added pun

Concur with Dave, Root rot, the adult form of damping off caused by one of a number of fungi (Rhizoctonia solani, Pythium sp., Fusarium sp., and Aphanomyces euteiches) Not much you can do about it at this stage. It is a common problem with Pisum species when growing in heavy wet soil. For future reference. The fungi overwinters in the soil, so try planting in a different well drained area. Treated seed helps a lot too. Whether or not to stake/stick is a personal decision. for the record I don't. Root rot does not care. Be aware that infected plants die quickly when the weather turns hot and dry.

The Soil is nearly sand, and does drain well, but we have had 9” of rain over two weeks, so it has been more or less continually saturated.

I've complained of our early heat this year, but I feel quite lucky that we aren't having the flooding. It's been one of the driest springs since we've lived here (not a bad thing considering the last 5 years we've lived here have brought monsoon spring rains). Everyone has a challenge of some sort I guess.