Figure 4: A farm in the Pontbren catchment

Figure 4: A farm in the Pontbren catchment (Forest Research, no date) The example of the Pontbren catchment in upland

Wales is a well-documented NFM project initiated

by farmers planting trees in the 1990s to create

shelter for their sheep (Clark, 2018). It provides

empirical evidence of tree planting increasing soil infiltration(Marshall et al., 2014). Two treatments,

removal of sheep and removal of sheep with tree

planting were compared to a control using

12mx12m plots for each treatment in four different sites. It was found that runoff was

reduced by 48% on the ungrazed plots and 78% on the ungrazed and tree-planted plots.

The median soil infiltration rate 5 years after treatment was found to be 67 times greater in

the plots planted with trees, compared to the grazed pasture. The scale of increase may

seem implausible, but grazing can create a thin near impermeable layer of soil and the soil

infiltration rates for the control areas were very low. The soil infiltration rates before

treatment were only measured once, compared to three times post treatment, so this may

add some uncertainty to the result. Hillslope studies elsewhere revealed soil infiltration rate

increases due to woodlands just 5-8 times greater than grazed pasture (Ford et al., 2020).

These studies were of mature woodlands compared to newly planted trees in Pontbren.

Furthermore, before reaching a conclusion on the differing results. there is a wide range of

variables to investigate, such as soil properties, topography and tree species composition.

Slow the Flow at Pickering is a Defra NFM pilot scheme in response to the 2008 Pitt Review.

Cost-benefit analysis indicated that a traditional engineered flood management scheme would not meet the thresholds for implementation. The main elements of the Pickering

project were bunds, but additionally there was planting of riparian and farm woodland and

installation of over 150 large woody debris (LWD) dams. The project was unable to meet its

planting goals for reasons discussed later. However, modelling showed that planting 50 ha

of riparian woodland and construction of 100 LWD dams would reduce the peak discharge

in a 1 in 25 year event an amount equivalent to 21% of the necessary margin to reduce the

flood peak to the level at which the town of Pickering starts to flood (Nisbet et al., 2015). It

is not a complete solution, but it would still be a significant contribution to flood prevention.