There are 10 locks on the River Murray. Locks 1-9 are controlled by SA, and lock 10 is controlled by NSW. In total there are 26 man made locks, weirs, barrages on the River Murray.
Lock One at Blanchetown is 274 km's from the Goolwa barrages. The distance between each of the other locks and weirs range from 29 to 88 km's apart. Below is a map with the locks and weirs located. Between the red location pins there is no weir or lock that can be used to control water levels.
From the map below it is very apparent that the river is narrow until it gets to Wellington where it meets Lake Alexandrina. Lake Alexandrina and Lake Albert require about 2000 GL to fill. Where as in other parts of the river, much smaller quantities of freshwater are required to keep the river levels elevated.
One more weir near Wellington would make this 274 km stretch of the Lower River Murray more manageable. This 274km stretch of water includes two very different environments: a river system from Blanchetown to Wellington, and the Lower Lakes system. A Lower Lakes system which could be restored to estuarine and allowed to become tidal again.
One more weir near Wellington, would prevent seawater from travelling up the Murray to Adelaide's water supply source, would make this stretch of river safer, and would pave the way for allowing the Lower Lakes to return to a healthier tidal estuarine system.
Take a close look at the map and notice the distances. Double click to zoom in.