Baseline survey of fluvial geomorphology and hydrology of Pipers River. Report prepared for the Tamar Natural Resource Management Strategy

There were three primary aims of this geomorphological assessment of the Pipers River. First, to evaluate hydraulic flow characteristics of the Pipers River at bankfull discharge. These are the conditions under which channel processes are most active, and channel erosion or avulsion can occur. Second, to describe downstream changes in particle shape and type of stream bed material, and third, to provide a baseline survey that can be repeated in future for quantitative identification of change. Three sites were assessed at representative sections of Pipers River. Site 1 was located just north of Underwood at 250 meters elevation and within a topographically steep landscape. Site 2 was located at Colgrave road, about 14 km north of site 1 at an elevation of 65 meters. Site three was east of Baxter road, further 8 km north from site 2, c. 11 km south from Pipers Head and at an elevation of c. 40 meters. The river at site 1 (Underwood) was found to be stable, with establishing riparian vegetation, and unlikely to erode. The river at site 2 was found to be unstable, caused by channel incision and expansion, leading to increased bankfull discharge and capability for erosion. This was exacerbated by large woody debris in the channel, in positions that cause bank scour. The river at site 3 was found to be unstable, caused by reduced bankfull discharge, and consequent bed aggradation, which has lead to channel avulsion. This was also contributed to by willow infestation of the channel, and stock access to the channel. There are specific recommendations from this field assessment to improve conditions at sites 2 and 3, including willow removal, riparian fencing, riparian revegetation, and rivercare assessment of the orientation of large woody debris at site 2, and the channel avulsion exit at site 3. It is further recommended that this survey be repeated in future for quantiative evaluation of changer, either after any major works (upstream or on-site), or every 5 years