The best single source design guides I've seen and used are the NAVDOC's series from the US Navy. If you're looking at small craft harbour facilities, NAVDOC's may be a bit overkill. There also are numerous excellent texts on the subject including:
Design & Construction of Port & Marine Structures, by Alonzo DeF. Quinn, published by McGraw-Hill Book Company, or
Floating Ports; Design Construction Practices, by Gregory P. Tsinker, published by Gulf Publishing Company.
Regards,