Effects of pipe outlet blocking on hydrological functioning in a degraded blanket peatland. Issue 3 (15th March 2021)

• Record Type: Journal Article
• Authors: Regensburg, Taco H.; Chapman, Pippa J.; Pilkington, Michael G.; Chandler, David M.; Evans, Martin G.; Holden, Joseph
• Is Part Of: Hydrological processes. Volume 35:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-15
• Subjects: discharge -- hydrological connectivity -- pipeflow -- restoration -- water table -- wetland; Hydrology -- Periodicals; Hydrology -- Research -- Periodicals; Hydrologic models -- Periodicals; Hydrological forecasting -- Periodicals; 631.432
• DOI: 10.1002/hyp.14102
• Languages: English
• ISSNs: 0885-6087

Abstract

Abstract: Peatland restoration practitioners are keen to understand the role of drainage via natural soil pipes, especially where erosion has released large quantities of fluvial carbon in stream waters. However, little is known about pipe‐to‐stream connectivity and whether blocking methods used to impede flow in open ditch networks and gullies also work on pipe networks. Two streams in a heavily degraded blanket bog (southern Pennines, UK) were used to assess whether impeding drainage from pipe networks alters the streamflow responses to storm events, and how such intervention affects the hydrological functioning of the pipe network and the surrounding peat. Pipeflow was impeded in half of the pipe outlets in one stream, either by inserting a plug‐like structure in the pipe‐end or by the insertion of a vertical screen at the pipe outlet perpendicular to the direction of the predicted pipe course. Statistical response variable η 2 showed the overall effects of pipe outlet blocking on stream responses were small with η 2 = 0.022 for total storm runoff, η 2 = 0.097 for peak discharge, η 2 = 0.014 for peak lag, and η 2 = 0.207 for response index. Both trialled blocking methods either led to new pipe outlets appearing or seepage occurring around blocks within 90 days of blocking. Discharge from four individual pipe outlets was monitored for 17 months before blocking and contributed 11.3% of streamflow. Pipe outlets on streambanks with headward retreat produced significantly larger peak flows and storm contributions to streamflow compared to pipe outlets that issued onto straight streambank sections. We found a distinctive distance‐decay effect of the water table around pipe outlets, with deeper water tables around pipe outlets that issued onto straight streambanks sections. We suggest that impeding pipeflow at pipe outlets would exacerbate pipe development in the gully edge zone, and propose that future pipe blocking efforts in peatlands prioritize increasing the residence time of pipe water by forming surface storage higher up the pipe network. Abstract : Blocking of pipe outlets in a heavily degraded UK blanket bog led to new pipe outlets appearing or seepage occurring around blocks within 90 days of blocking. Two pipes at head locations contributed more to streamflow compared to two pipes at edge locations, altogether they accounted for 11.3 % of streamflow. The degree of water‐table drawdown in gully edges is thought to relate to piping activity. Peatland practitioners should consider control measures that reduce pipeflow further upslope of pipe outlets.