River Arevass is a river located in Silverpine Forest, just west of Lordamere Lake. It was where Tyrande made a stand against invading Scourge, which ended with the bridge spanning the river breaking and the high priestess being swept downriver.
In-game Possibility
In Silverpine forest, there is the remains of a river that once flowed either in to or out of Lordamere Lake. All that remains of it is the dried up canyon, a few remaining pools, and a human bridge crossing it near the lake its self. This is possibly the Arevass, and its drying up could be due to a hypothesized fall of water around the time of Warcraft 3 that could have also eliminated Cross Island. It seems to have flowed in, because of there being no trace of its flow between the canyon and the seashore, and the canyon hints that it was a fast flowing, highly erosive river.