Simplify the following text for a Grade 7 native English-speaking person.
Original: The Salt River runs westward through the city of Phoenix ; the riverbed is often dry or a trickle due to large irrigation diversions , except after the area 's infrequent rainstorms or when more water is released from upstream dams .
Simplified: The riverbed is often dry or just a trickle due to large irrigation usage . The river is full after infrequent rainstorms or when more water is released from upstream dams .