Shade from trees is really important to keep rivers healthy for a wide range of wildlife. We are looking at areas across Essex where we can make an improvement.
The benefits of shade
Stretches of river without shading from trees can be several degrees warmer in the summer than those with tree cover. Over the coming decades summer river temperatures will rise further, causing a real threat to species including trout that thrive in cool water. Limiting sunlight on the water surface also controls the level of weed growth that can be detrimental to having a balanced ecosystem, and less weed can mean reduced flood risk without potentially harmful weed-cutting operations. Locating suitable sites for tree planting and doing it now will help to protect our rivers from future climate change.
Trees also provide great habitat along the river corridor, and when branches break off and fall into the water they can change the flow and provide shelter for many species. In the right place, trees can be the answer to many problems we face.
Where did all the trees go?
In a lot of places, rivers have been deepened, widened and straightened to drain land and prevent flooding. This often included removing trees along the river bank. We now have a much better understanding of how rivers work than we did generations ago, and we have the opportunity to look at the whole catchment. Rather than looking in individual locations and trying to “dispose” of the water downstream and ultimately out to sea, we aim to manage entire catchments to slow down the run-off and hold water in certain areas. This should mean less flooding, less severe impacts during dry periods and better habitat. There will always be a place for flood defences and dredging, but there is also a place for trees and wetlands.
A modified, straightened river channel with very little tree shading.
A restored river channel with good tree shade. Great habitat.
How do we know where to focus with tree planting?
We have worked with Essex Wildlife Trust to carry out walkover surveys of some Essex rivers (see HERE for more info) and we have some great information on shading, land use etc as a result. More recently we have been given a great dataset by our Geomatics guys showing comparative shading in all our catchments. This gives us a powerful tool to focus our efforts, but how does it work?
The science bit
It is all thanks to LIDAR (LIght Detection And Ranging) technology used to generate detailed flood maps across the country. The equipment is installed in aircraft and lasers are used to measure the distance from the aircraft and the ground surface, producing highly accurate 3D models. This allows us to refine flood maps, improve flood warnings and to give advice for planning new development that could be at risk from flooding.
Our Geomatics team use light aircfraft equiped with LIDAR kit
Some of the clever kit that helps to manage flooding and improve habitat.
The two main types of LIDAR outputs are the Digital Surface Model (DSM) and Digital Terrain Model (DTM). The DSM includes surface objects such as buildings, vegetation etc and the DTM has these removed to show the “bare earth” ground level. We can remove just the buildings from the DSM to leave us with a model showing vegetation, compare it with the “bare earth” DTM, factor in the average solar energy for the area and create relative shade maps. Very clever, complex work but the outputs are easy to understand and very visual.
Example of a Digital Surface Model (DSM) at Cymbeline Meadows, showing all surface features.
Example of a Digital Terrain Model (DTM) at Cymbeline Meadows, showing the “bare earth” ground level.
An Essex example
I recently met with Paul from the Essex & Suffolk Rivers Trust to discuss what work we may be able to do with Colchester Borough Council along the River Colne at Cymbeline Meadows, Colchester. I consulted the Geomatics LIDAR data and it clearly showed a comparative lack of shade through the parkland. This means that for relatively little money and working with volunteers we can plant trees alongside the river and make a big habitat improvement over time.
Click on the image to open a pdf map you can print or save.
I took a lunchtime wander along some of the “red areas” on the map. The good news is that the science works and the shade map was spot on. Also where there are trees by the river, there is a good source of woody debris as well as shade. The bad news is the distinct lack of trees on the south bank as can be seen on the second photograph below.
Where there are trees, some branches are in the channel creating the woody debris of the future. Perfect!
The lack of tree shading on the far (south) bank at Cymbeline Meadows is something we can address.
What next for Cymbeline Meadows?
We have used our LIDAR data and local knowledge to find an area lacking in shade, confirmed that it does need some love and attention so now we need to do something. We will be working alongside the Essex & Suffolk Rivers Trust and Colchester Borough Council, pulling together a plan to increase the shading of the river channel as well as any other affordable modifications that can be put in place with the help of local volunteers.
Watch this space as the project takes shape!