Comparison of methods for measuring woody riparian vegetation density

Flow resistance caused by vegetative drag depends on vegetation density (Veg(d)), the area of vegetation projected onto a plane perpendicular to the flow direction per unit volume of flow. However, research concerning the accuracy and efficiency of field measurement of Veg, for hydraulic investigations is limited. Measurements were conducted at two willow stands with different Veg, using the horizontal point frame (HPF), board, and camera methods. Results obtained with the HPF method were considered accurate and used as a standard with which to compare the performance of the board and camera methods. It was concluded that the board method: (I) was the most rapid of the three; (2) tends to underestimate Veg(d); and (3) performed better in sparse willows than dense willows. The camera method: (1) required less time than the HPF; (2) tends to underestimate Veg(d); and (3) performed better in dense willows than sparse willows. (C) 1998 Academic Press Limited.