The Trinity River drains approximately 17,500 square miles of north-central and eastern Texas. Its average annual discharge is 5,166,000 acre-feet and in water year 1965 it carried 5,308,000 acre-feet of water. The river's average annual suspended load contribution to its delta is roughly 3000 acre-feet. During 1965 over 50% of the Trinity River's discharge and over 60% of its suspended load were transported by two major floods. The suspended material delivered to the delta contains about 25% sand, 30% silt, and 45% clay.