PRICES at the New Territories' Riviera Garden dropped in August, according to provisional figures provided by Brooke Hillier Parker. In keeping with the trend for the previous six months, the average price was estimated to have dropped a slight $5 to $2,845 per square foot. ''Since February, prices have not really moved that much,'' said BHP Research partner, David Faulkner. He expected prices to remain the same or drift down slightly until the next buying spree in spring next year. The trend in price movement is not dissimilar to last year's course, he said, adding: ''Buyers are pausing for breath.'' Tighter lending restrictions imposed by the banks, lack of available capital, and general disinterest are thought to be reasons for the stagnating price.