Thursday, 8 December 2016

Trees and flooding

At the Arboretum's recent tree event
Futures Forum: A Celebration of the Sid Valley’s Trees >>> Protect - Improve - Expand!!

... there were several talks touching on interesting and vital topics:
Futures Forum: The impact of grey squirrels on East Devon's woodland

District Council Warden Laura Goble looked at the interplay of planting trees and keeping flooding under control. 

Here are links to pieces from the Woodland Trust:

How trees can reduce the risk of flooding

By Mike Townsend , 4 February 2014

Recent flooding has highlighted the importance of land use in either contributing to or mitigating flood risk. In particular the suggestion that trees might play an important role in helping reduce flood risk.

Reports from the Woodland Trust on water and farming and water in towns provide a review of the evidence for the role of trees. Forest Research has also undertaken a significant amount of work looking at the role of trees in delivering better water quality as well as modelling the impacts of increased tree cover on flood risk. These show that trees can make an important contribution both to mitigating flooding and improving water quality.

How trees can reduce the risk of flooding - Woodland Trust 

And the US Forestry Service:

F L O O D I N G and its effects on TREES
Flood Tolerance of Trees

Numerous studies have been conducted to help foresters and natural resource managers understand the impact of flooding on trees (see bibliography). 

The state-of-the-art, however; has not developed sufficiently to warrant a precise statement on the adaptability of a species to a specific flooding situation. 
Conclusions from different studies are often contradictory, caused in part by the physiological responses of the tree as it interacts with environmental conditions. 
Since these environmental conditions are not well understood, as well as the difficulty in categorizing tree species over their entire range, flood tolerance predictions must be carefully evaluated in general terms. 
A brief review of soil, tree, and flood characteristics indicates the complexity of these interactions.

FLOODING and its effects Trees, Flood Tolerance of Trees

And this is the Abstract of Laura Goble's BSc Thesis:

Does Tree Restoration Affect Catchment Hydrology

This study investigated the influence of tree restoration on catchment hydrology using a paired catchment approach in the Southern Uplands, Scotland. Situated upstream of the town of Moffat, the Carrifran catchment has undergone planting since 2000. Ecological restoration is the primary goal, although sustainable flood mitigation for Moffat may be enhanced, as trees reduce water yield and influence the partitioning of water into different hydrological pathways by which rainfall reaches watercourses. The impact of tree restoration was evaluated by comparing data from Carrifran with the adjacent grazed catchment of Blackhope. Data were collected on 10 sampling days between July and October 2014. 

Slope aspect, elevation and gradient were incorporated into the experimental design and statistical analyses. Rainfall was measured at varying intervals using a storage gauge. Initial state infiltration capacities were measured using a single ring infiltrometer and a constant head approach. The moisture content of soil samples was determined using the gravimetric method. Hydrological pathways were determined by hydrograph separation using electrical conductivity as a natural tracer. The catchments had significantly different infiltration capacities when different associations between elevation and infiltration capacity were taken into account, suggesting enhanced soil water storage capacities in Carrifran. The temporal variability of soil moisture content and infiltration capacity corresponded to rainfall more readily in Carrifran than in Blackhope, suggesting surface sealing in Blackhope. Rainfall was the dominant contributor to streamflow in both catchments, indicating that the impacts of tree restoration may not yet be as extensive as expected.

For the complete work, see here.

See also:
Futures Forum: Fences: a sign of creeping urbanisation > plant more hedges

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