original: The town was built on the mouth of a small tributary; the High Street once met the water at the top of the river.
simplifications: The town was built on the shore of a small river. The High Street once met the water at the top of the river. The town was built on the mouth of a small tributary. High Street once met the top of the river. The town was built on the mouth of a small tributary. The High Street once met the water upriver. The town was built on the start of a small tributary. The High Street once met the water at the top of the river. The town was built on the mouth of a small tributary, where the Street met the water at the top of the river. The town was built near a small body of water. The town was built on the mouth of a small tributary. The High Street once met the water at the top of the river. The town was built near a small tributary. At the top, the High Street once met with the river. The town was made at the start of the waterway; High Street once met the water at the top of the river. The town was built on the mouth of a small river. There was a time that the High Street met the water at the top of the river.