Comparing the NFM potential of standard and optimised peat blocks used in peatland gully restoration

Extensive erosional gully networks are commonplace in degrading peatlands. Gullying produces local water table drawdown and the increase in drainage density associated with gully networks increases hydrological connectivity between hillslope and channel. Peatland restoration methods commonly involve blocking of gullies with peat or timber dams to limit further erosion and promote higher water tables. Blocking is also demonstrated to attenuate channel flow in peatland catchments, suggesting that gully blocks can provide Natural Flood Management (NFM) benefits. Block design can be further optimised for flood attenuation purposes, such as including an outlet pipe through the block to provide dynamic in-storm storage. 

This paper compares the hydrological functioning of standard peat dams and piped-peat dams optimised for NFM from neighbouring microcatchments (<2.5 ha) in the Peak District National Park, UK. Pre-restoration discharge was monitored for 12 months prior to installation of 6 standard peat dams in one microcatchment and 10 piped-peat dams in the other. Bottom of reach discharge and individual dam pool height was recorded for the following 12 months. The series of piped-peat dams are demonstrated to have a higher impact on catchment discharge than standard peat dams, reducing peak discharges and increasing lag times. Standard peat dams provide little storage volume during storm events compared to the dynamic storage provided by the outlet in piped-peat dams. However, the requirement for maintenance of pipe-peat dams is identified, with pipe blockages compromising dynamic storage. These findings have implications for understanding of NFM benefits from standard and NFM optimised peat dams.