My understanding is that the 'silting up' you point are high...

My understanding is that the 'silting up' you point are high parts deliberately there. The ponds were designed for the water to flow through a series of esses like a snake. The flow rate would drop and the silt would be mostly in the early cells. At the top of the picture every second causeway should have a break and at the bottom of the pic there should be a causeway every second one.

Some 'numnut; decided to take the esses out and allow the water to flow straight through. I think this was done to make it easier for an excavator to get out to the causeways to desilt and never returned to original condition.

The end result is the same as HoM points out and that is that there is little to no desilting being done with this feature.