If you use shell grit zise 5-10mm preferably on top of geotextile,the layer should be 12-15cm(5-6 inch) thick, you will get a nice beach like entry point that lasts 10-15 years it will also be a nice Ph buffer for the pond.
This is all pics of beaches buildt as described in the sea and ponds
http://www.sandstrand.no/highslide/sandstrand_bilder.html

cheers

PAUL