I did end up making my improved river pump inlet.

Here it is!

So, same idea...two metres of polypipe with millions of small holes drilled into it. But instead of one unwieldy length it has four short arms. The holes are drilled in graduated sizes....tiny holes on the bottom end nearer the base of the river bed, and larger holes at the top end of the pipe. I am working on the theory the silt is closer to the river bed. Doesn't always work that way when there is a current.... I also didn't drill any holes directly at the bottom, with the aim to reduce the amount of silt/sludge that gets picked up.

The connection to remove it is now the camlock fitting. (Not shown in the pic...it is screwed into the galvanized T fitting in the middle of it all.) It means I can simply unclip it very quickly. I still have to go into the water to do that, which isn't hard this time of year, but afterwards it occurred to me if I put another camlock on the shoreline I could unclip and drag it out of the water without getting wet. ( Sounds simple....I weight the inlet down with a brick, and thread it under a log so it doesn't drift. Dragging it out might not be possible without getting tangled up.)

The pipes are cut unevenly, as in different lengths. With the camlock fitting I can spin the inlet any angle, so I now have the ability to position the device on whatever shape I want!

It has worked a treat. After it rained and the river took up a rush of water the pump started to slow down in terms of delivering water. I went into the river and pulled the inlet off, gave it a quick flush, and the pump hasn't missed a beat since.