The interim data from the experiment is available on the OPW website here [seven-page PDF]. The conclusion is:
From the water level records, it is apparent that the closing of the gates at Athlone weir in anticipation of a rise in water levels on Lough Ree led to a temporary lowering of the Shannon water levels immediately downstream of Athlone. This possibly delayed inundation of the Shannon callows downstream of Athlone by a number of days. To determine whether the extent or depth of eventual inundation was in any way reduced by the experiment will require more detailed analysis by the CFRAM consultants. Data is available on request from Hydrometric Section if required.
It should be stressed that this is an interim report. This CFRAM background document [PDF] is still useful.
It is not clear to me why the state should spend any money improving the value of privately owned riverside land that is of marginal benefit to the economy.