Difficult to manage salinity concentration, because sea water during tidal entry periods is heavier than freshwater, and estuaries probably have little mixing and the freshwater unless mixed rides over the sea water.  If your goal was to maintain or reduce salinity, then you should time your stored freshwater releases so they will be hitting and raising the water level in the estuary before the high tides, and during low tides, you will not need to release so much freshwater from storage.  You would have to figure out how the fast the water moves from storage to the estuary. Your control of salinity with freshwater will be limited unless you also plan on controlling tidal inflow to some degree, or releasing enough freshwater to overpower the tidal influence.  

Thank you Mr. William, can i know some reading materials relate to this?

Sluice gates are effective ways for preventing tidal currents to intrude inland. You can look at the design of the gates such as Oshiba or Gion Sluice Gates built on Ota River Estuary, Hiroshima, Japan. 

In fact, the Ota River discharge is not high (less than 100 m3/s), so to control the length of tidal compartment sluice gates are built. The only consideration  is proper management of the gates operation.

Most of this management I have seen related to rice culture in SC, and various articles or books that mentioned small pieces on the subject.  I dont remember a manual on the subject, but will check.  Just so you know, there can be ecological changes in modifying hydrology, so it is best to check if you need permissions or permits.  Coastal waters are some of the most productive habitats, often limited in extent.  Salinity shifts may affect some of these habitats.  

Again. Thanky you very much, Mr William and Mr. Mahdi