Seeking Machinery to Remove Sludge from Under a 20 meter Long Bridge

The river water passes through a wide water channel in the city limits to reach the pond, the channel has more bridge, intersecting the roads of 20 - 30 meter wide. Since the river passes through the lively hood - the sludge were deposited, garbage and waste are blocking the water flow. The blocking stuffs were removed on the open area, but could not even attempt to remove the sludge under the bridge. We measured that the sludge deposited is about 1-2 meter high through out the 20 meter tunnel/ bridge. Seeking the experts help, of how to remove ? - Which machinery or any other manual tools to remove the same. Attached are the pictures for reference.     Also, please note that, removing the sludge/debris after a decade time means - allowing the river water to a 100 acre pond - Which recharges the underground water for 10,000 acres of agricultural land.   Thanks Murthi