Examples of Official useage: 
 United States: 
 * Henry Kissinger: The Soviets maintained a position of neutrality in the recent dispute between Iran and Iraq over the Shatt al-Arab River 
 * US State Department Background Notes on Iran: Much of the dispute between the two countries centered around sovereignty over the waterway between the two countries, the Shatt al-Arab 

 United Kingdom: 
 * Iraq travel advice: The boundary between the territorial sea of Iran and Iraq at the mouth of the Shatt al Arab waterway has been a matter of dispute between the two countries for a number of years. 
 * Ministry of Defence: The helicopter reported that the two seaboats were being escorted by Iranian Islamic Revolutionary Guard Navy vessels towards the Shatt 'Al Arab Waterway and were now inside Iranian territorial waters. 

 I cannot find any reference to Arvand under any spellings on the US State Department, the British Foreign Office or the British Ministry of Defence websites.