Well guess trying to look at the bright side at least with flood irrigation at least you don't have a ditch in the field every 34 inches like I do..

I would really suggest trying the P.A.M. especially if you're thinking of a preplant wet up to green up the weeds as the ground has set dry/idle for so many years.  I don't know how many feet/sec or gph you have available how fast it runs in,, but even if you get a "fish feeder" (chem dealer or such should know about P.A.M./fishfeeders etc..?) find a way to get the P.A.M. into the inflow water it will help with the water flowing "across" the field vs trying to go down into the soil profile. 

I talked to a neighbor who was short on options so he simply took a gunny sack poured a 2.5 gal container of P.A.M. into it tied the top closed with some baling wire and suspended it in the water flow running into his field. He was irrigating with gated pipe and ditches and thou not "perfect" it did work,,,,, right till his "farmer fix" baling wire hanger broke- and the entire gunny sack and "goop" of P.A.M. floated down into his gated pipe and plugged the dang thing... 

In my circumstances the canal water is brown with turbidity (runoff from fields up canal) and full of trash. At times it looks like a person could literally walk on the water it is so full of that super fine silt..  I have to screen the water with screen door screen right at the weir blade and as soon as the water passes the wier blade I'm metering in the P.A.M with a battery operated (12 volt) machine. P.A.M. is "most" effective right at the initial startup watering. Water starts, P.A.M. machine is already running. At the end/bottom of the field, the water is clear enough to see the bottom of the individual ditches and turbidity is just about zero. Using P.A.M. I get very close to zero soil movement even thou there is a small ditch carrying water downhill every 34 inches. Even the ditch rider has said my return water is cleaner than the water going into the top of the field from the irrigation canal.

Here's a link to an online book about P.A.M. use in the Kittitas Valley.

http://books.google.com/books?id=NOnolCgrYXoC&pg=PA47&lpg=PA47&dq=Polyacrylamide+kittitas+county&source=web&ots=1asm7-3ubZ&sig=gVU7ihqwnGYpsC-ti-K1J8mWdzw&hl=en#PPA7,M1

 I think it's fairly comprehensive study discussion (boring..) but there is some good info in it.   I only have dial-up (at best 42K which sucks) so didn't look at the entire book.  They talk about infiltration (from what I did read..) but don't know if they discussed- show that P.A.M. does help allot with the horizontial infiltration and as I talked about earlier, down to about 8 inches then the soil structure and physical property's of the water with PAM in it does slows down the infiltration below the 8 inch level. So, the water actually spreads out horizontially quicker with PAM.

I admit I don't get really "techie" about the application rate,, I stick my hand in the water a few feet past the applicator and if the water feels "slippery" and the water is clearing up that is about right.  I use the dry powder/granular type.

If the water turns into "buffalo snot" you know it's mixed a wee bit too thick... LOL.. don't ask how I know that..

No,,I don't get a plug nickle for suggesting the PAM.. I just know it works well an I use it.

 Oh,, check with your local NRCS office (assuming you have one) there is $$$ available to offset the cost of the PAM. (locally they pay 50% of the purchace price)

Probably 1/2 page more than you were interested in reading???