Settling basin design 1

[Kuhuh]

Simple facts, its a realistic problem my boss is letting me try out to learn;
In a canyon, designing intake structure for domestic water retrieval. Intakes will be CMP risers protected with gates and settling basin up stream. The canyon has lots and lots of boulders and rocks, a settling basin is used to help reduce amount of boulders crashing into intake risers, gets cleaned out during dry season. Questions how and what size of boulder do I design for settling basin for? is there a procedure to determine a gradation curve by visual inspection? Do I design for 95 percentile or largest diameter. My thoughts would be I should design for a rock that's in the 95 percentile with a factor of safety of 1.5 and I can't find if there is an acceptable code or procedure on how about finding a gradation curve or way to categorize what size the 95 percentile is, can anyone help?

 

[gbam]

You should evaluate your rock diameters based on rate the basin fills up and requires dredging. Also you will be looking for nthe smallest diameter rock you are looking to trap, not the largest. You will need to know what your sediment (Rock/Boulder) yeild is; this can be a % or actual weight/volume. This will dictate your settling basin volume.