What are the Causes of Rapid Sand Filter Clogging?

Hello, I am working with municipal water treatment facility in Delhi, India. We are facing a huge problem at our water filtration plant as sand filters are clogging/choking every 4-6 hours. This problem is making our water filtration vulnerable and we need to backwash the filters multiple times per day. This is harming our water treatment efficiency. Can anyone suggest a reason behind it and, if possible, a solution? Please help.