Why was heavy funding needed to enforce the volstead act?

It was needed because alcohol was being smuggled through the coasts. In addition, many people were involved in the bootlegging business. Volstead Act is to prohibit intoxicating beverages, and to regulate the manufacture, production, use, and sale of high-proof spirits for other than beverage purposes, and to ensure an ample supply of alcohol and promote its use in scientific research and in the development of fuel, dye, and other lawful industries