I presume you have looked at the reviews so a good place to start would be to have a look at the Abou Sofiane thread and get as much info regarding the beach and location etc from it as you can viewtopic.php?f=27&t=119593&hilit=riviera
The hotels are located beside each other, the Abou Sofiane is located directly on the beach with the Riviera just behind it, access from the Riviera to the beach is down the side of the Abou Sofiane.
The two hotels used to be sister hotels and guests were able to use the facilities at both, however the brother and sister that own them had a fall out and they now operate as totaly seperate hotels.
There is a nice sunny pool at the Riviera with the usual activities organised by the animation team, the beach is lovely with plenty of sun beds and water activities.
The Riviera is about a 15-20 minute stroll either along the road or along the beach in to the centre or marina area of PEK.
As far as I am aware (I might be proven wrong) but I am sure the Riviera is the same as the Abou Sofiane and you have to hire a fridge for a small fee and you get a bottle of water a day for the room.
Take a look at these pictures for an overview of PEK http://travel.webshots.com/album/568540283GrfKwP