Reverse flow in vertical shaft pumps

I've to dewater a reservoir to sea by using a wet pit mounted vertical
shaft pump (axial flow), for watering the same reservoir i want to
eliminate the extra pipe way and channel as there is positive head over
the reservoir (sea level is 2.5 meter avove the reservoir)i am planning
to use the dischrge flnge of the pump as the suction from sea to
reservoir without runing the pump, Does anybody know what will happen to
pump bearing wise?? Anyhow is it practible?? Please let me know about
any remedies or cautions!!
Thanking you in advance.
If the pump motor is over the sea level, you have the first problem solved.

Normally the pumps have a check valve on the discharge side if it is so you must take it off.
BUT
The
first to be aware is than when the water goes back the pump , the shaft
will rotate in counter wise from original and the threaded parts could
disassembly.

If you want to use the same pipe , use a check valve
upward the pump and do a tee branch where to put valve , so when the
pump is off you open this valve  and can fill again your reservoir.
Dont worry about your english , mine is not better.
And you could fit a hold back on the pump drive so that it can only rotate
in the desired direction. When the flow reverses the water will go
through the pump. Be careful to check how the impeller is secured to the
shaft. Sometimes they are simply screwed on and flow reversal can drive
the impeller off the shaft and it will foul the casing.

Check with pump manufacturer.

Discharge check valves could be replaced with an actuated valve so flow could be stopped in reverse if required.
From the originalCheck Valve
.