Canyons are inherently risky. Flash floods occur without notice on sunny days. Technical skills & surrounding topography knowledge required yet does not eliminate risk.
Overview: A full trip down the beaUTiful Kolob Canyon from the West Rim TH to the Zion Narrows and down to the Temple of Sinewava is best done over two days. Due to it being downstream of the Kolob reservoir, it's flow it regulated by the Washington County Water Conservancy District and you need to check with them before getting permits and dropping in. Bring thick wetsuits and enough rope for rappel up to 165ft...
Check out the Triplog.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.