There is a company called piranha that makes agitator pumps and very small dredges. The silt can be pumped into filter bags and left to de-water on the bank next to the pond. When dry, the bag is cut open and the dry silt can be excavated and hauled away. you may want to build silt traps at the inlet using silt fence or wattles. These act like little dams before the water gets to your pond where the water velocity is slowed and silt can settle out and then you would clean out the traps with a backhoe as they fill up, keeping the silt from reaching your pond in the future.
