How to find out if a ship has entered shallow water?

Entering in the shallow waters considered very dangerous for a merchant vessel.Special precautionary actions are taken for shallow water regions.The most common and accurate ways to know the depth of sea or under the keel is using Eco meter.In case of any malfunction of this device there is some certain ways to find out whether the ship has entered the shallow water on not?
Some ways are described in the following :-
1. Wave generation from the bottom of the ship increases, especially at the forward end of the ship.
2. Ship becomes more sluggish to manoeuvre.
3. Draught indicators or echo-sounders will indicate changes in the end draughts.
4. Propeller rpm indicator will show a decrease. If the ship is in “open water” conditions i.e. without breadth restrictions, this decrease may be up to 15% of the service rpm in deep water. If the ship is in confined channel, this decrease in rpm can be up to 20% of the service rpm.
5. There will be a drop in ship’s speed. If the ship is in open water conditions this decrease may be up to 35%. If the ship is in a confined channel such as a river or a canal then this decrease can be up to 75%.
6. The ship may start to vibrate suddenly. This is because of the water effects causing the natural hull frequency to become resonant with another frequency associated with the vessel.
7. Any rolling, pitching and heaving motions will be reduced as ship moves from deep water to shallow water conditions. This is because of the cushioning effects produced by the narrow layer of water under the bottom shell of the vessel.
8. The appearance of mud cloud will be visible in the water around the ship’s hull when the ship is passing over a raised shelf or a submerged wreck.
9. Turning Circle Diameter (TCD) increases. TCD in shallow water could increase 100%.
10. Stopping distances and stopping time increase, as compared to when a vessel is in deep waters.
11. Effectiveness of the rudder helm decreases.
If the situation match with the above described conditions special cautionary step must be taken in order to prevent any unwanted situation.