If you are trying to introduce waterlilies as a break water, rooting them in sand and gravel, that may well be a disappointment ... if the lily pads are constantly being rocked by water motion the roots are persistently being tugged and flexed, as the all important roots on water lilies are the brittle feeder roots they are being systematically ground to shreds...
Additionally waterlilies really hate persistent water motion, they don't like the top side of the lilypad constantly wet, it seems to interfere with the health of the plant if the waxy coating top side is always wet.
You may have better luck trying nuphars, they cope with moving water unlike the nymphaeas... to the extent they can cope with a strong flowing river.
If you can plant a breakwater of say a line of aquatic iris, or create a structure which can act as an effective breakwater, hardy waterlilies stand some chance of establishing if most of the time, the water is still...
One way to cope with the existing situation might be to start tubs waterlilies off in a quiet still location, get them growing strong then boat them over to the exposed position and drop them in, perhaps after establishing a breakwater effect with with composite positions of nuphars, iris, and structural barriers, perhaps a pleasant opportunity to design an attractive 'hide' or sundeck with a picturesque bit of timber decking, standing on pilings easy to drive into the dratted sandy bed
Regards, Andy
