B) THE WORKS ON THE RIGHT BRANCH
pict.B1 - The 'bridles' and the threshold under Ponte CestioThe problem was faced and solved by  the engineer Luigi Cozza that restored the balance in the two river branches reducing the flow in the right one by the construction of  two "bridles" under the lateral arches of Ponte Cestio and apict.B2 - The threshold moved dowstream Ponte Cestio thresholds under the central one (pict.B1), the last also with the purpose to limit the drag effect of the riverbed.
The "bridles" are still visible in the original position, while in 1994 the threshold has been moved downstream (pict.B2) creating the characteristic waterfall (see D1)