Engineer Malcolm Alli in his most recent letter to SN (January 13) again reiterated that the 7-door sluice was designed to release water to keep the Abary River “alive.” In my junior years I worked on the MMA project and frequently traversed the Abary River between the Public Road and Copeman (the site of the sluice). I do support Engineer Alli on this pronouncement. To the best of my knowledge the 7-door sluice was designed to serve the following functions/operations: (a) to control the saline (salt water) front into the Abary River (b) to act as a flood control structure and to supply irrigation water to the lower reaches of the river and (c) to operate as an emergency release structure.
A minimum discharge was predicted to limit the saline front from travelling upstream based on observations during a few months of dry period in the early 1980s. Saline front penetration for both the neap and spring tides was predicted. The neap tide, being the worst case, caused the saline front to travel upstream as far as the railway bridge.
The only time the sluice was allowed to remain closed was in the event of a storm having a defined amount of rainfall in the lower catchment area. According to Engineer Alli the authority claimed that the river was “alive and free flowing.” In principle “keeping the river alive” means maintaining the river regime, limiting the effects to flora and fauna and artificially controlling saline intrusion to the limits specified. By “free flowing” my interpretation would be to avoid no flow zones, especially where the river was dammed.
What is the source of the free flow water? If the MMA authority is saying that the tidal flows are keeping the river alive and free flowing then the tidal fluctuation is felt all the way to Copeman. Are they serious?
Where is the saline front today during the extreme tides? In my opinion there is a grave operational mistake being made. The project is therefore not meeting its environmental expectation and the appropriate agency responsible for monitoring post-project environmental impact should kick into gear.
If the Abary River is alive and free flowing it would mean that there is rainfall almost every day in the lower catchment area equal to or exceeding the predetermined rainfall amount set in the design document. Can the MMA attest to this fact? Dredging has been touted as the preferred option to restore the river regime but would we have solved the mystery surrounding the minimum discharge from the sluice? In another few decades we are bound to repeat the dredging exercise or we would have lost a river.
Some questions that come to mind are: (a) Is the MMA making use of the O & M manuals or the engineering design reports that dictate the operation of the sluice and (b) where are these documents today?
I would urge the GOG to get serious about the environment and have projects managed in accordance with the design unless additional studies/exercises prove otherwise and are documented as such. As engineers we owe it to the public to safeguard their health and safety. How much longer will the public have to wait for the engineers who also worked on the MMA project (design and construction) to speak on such an important environmental issue?
Ralph V Seegobin