Task 2. New observations to inform the modelling and fill unacceptable evidence gaps
The investigator team, working with partners delivering NFM, will collect new field-observed evidence of hydrological change at NFM-feature scales. This will add to the existing scientific evidence base filling knowledge gaps and increasing our confidence in subsequent modelling results.
Specific tasks:
Our experimental work to address component objective 2 combines a paired-plot experimental design and a <1 km2 micro-basin experimental design.
Task 2.1 Paired-plot experimental design: Many catchment hydrological parameters and variables are typically measured with instruments at sub-plot scales and a statistical distribution of these data integrated to plot scales (e.g., soil permeability, wet-canopy evaporation, soil moisture content etc.). We propose to adopt this established approach, and standardise by placing 20x20 m square plots in pairs either side of boundaries of sites reflecting the sorts of changes arising from an NFM intervention. For example, a plot in intensively-managed grassland, close to the boundary of a conifer plantation, where a second plot would be established. The side of the plot closest to a landscape boundary would be located 20 m from the boundary to reduce edge effects. We would address many different types of contrast across boundaries e.g., stock exclusion from intensively grazed hill grassland (potentially affecting roughness and soil moisture content - from our work with partner Woodland Trust on Tebay Fells, Cumbria); peatland restoration on plot-scale surface roughness and soil moisture content (with partner Cumbria Wildlife Trust); effect of established conifer plantation on soil permeability, moisture content, surface roughness etc. versus moorland or intensively grazed hill grassland (with partner Forestry Commission England - building on our ongoing studies in Whinlatter Forest with the FC). The exact mix of contrasts across boundaries to be studied will depend on a combination of the gaps identified in the evidence base (Task 1) and on the suggestions and needs of our partners (Task 7.1). A range of topographic locations (crest, hillslope and valley floor) would be needed to constrain spatially-explicit model estimates (using observed soil-moisture and flows).
Task 2.2 Micro-basin (<1 km2) experimental design: Observing change in flood peaks within continuous riverflow records as a direct result of a single landscape intervention is perhaps the 'gold standard' for evidence of intervention effectiveness. Observing such changes (that can be attributed to a single intervention) at the scale of a large river catchment is, however, rarely possible because: (1) the landscape intervention typically does not cover most of the basin, (2) natural dynamics in rainfall-streamflow behaviour may mask the intervention effects, (3) the effect of the intervention on the hydrology sometimes needs to build over time e.g., due to tree growth, and/or (4) a nearby identical reference or control catchment monitored parallel to the catchment with the intervention is often difficult to find. By reducing the size of the catchment to be monitored to closer to the scale of the intervention, say perhaps 0.5-1 km square, may allow many of these issues to be better addressed. The cost of installing a new gauging structure on a stream when the basin area significantly exceeds 1 km2 becomes restrictive and beyond the scope of the project resources. Because changes in flood hydrograph shape may to be relatively small, if gauging is undertaken at sites without a control structure (e.g., an environmentally acceptable trapezoidal flume), the uncertainties in the rating relationship may be large and so mask true differences in hydrograph shape between a basin with an intervention and either the control basin or pre-intervention state. Consequently, for this study we propose to standardize the design of all our new field experiments to show flood peak change with the use of the identical trapezoidal flumes capable of containing 435 L/s (suitable for gauging micro-basins <1 km square).
Installing the micro-basin flume at Fellsike Gill