In the following opinion piece, Richard Horrocks (pictured above at a river activity day) responds to the River Culm Environmental Evidence Review. Richard’s career was spent with the Environment Agency and he is currently Riverfly co-ordinator for the Culm and Lower River Exe Catchment.
I welcome this Review, which brings together the many issues facing the Culm catchment. It presents data that would not otherwise be readily available to the public, or requires specialist expertise to obtain and interpret so that they can be understood. Of course finding the ways and means of addressing these issues will provide an even greater challenge, but having an integrated approach is undoubtedly the right way given the complex relationships between them.
If I have one major concern it is that the proposed conclusions will not be integrated enough. A way forward that is basely solely on nature-based solutions can only be partially successful. We cannot hope to see the catchment achieve its potential if matters including agricultural policy and the effectiveness of environmental regulation are not addressed.
I shall confine myself to three issues: resilience to flooding, water quality and biodiversity.
Improving Resilience to Flooding
My professional experience of dealing with flooding in this catchment extends over 30 years and includes hydrology, flood defence and management.
By far the most effective measure to address flooding is to keep vulnerable development out of the floodplains and, by and large, this has been achieved in the Culm catchment. Most flood defence measures have been a response to ‘inappropriate’ development, albeit some of it historic. However the pressures for development continue, hence the need for effective planning regulation.
Flooding is itself natural and cannot be stopped. We can reduce some kinds of flooding, such as from surface water and sewers, and we can make local improvements to hold back water and improve ground infiltration, but there are no measures that will significantly reduce major flood flows. These are functions of the weather and catchment characteristics such as slope and soil permeability.
Restoring excluded floodplain can be an effective measure but there is very little of this on the Culm. The limited flood-banks and other defences are local and protect communities, not farmland.
Unfortunately, measures such as tree planting on the scale suggested can have very little effect on flooding and could make matters worse. An additional 125 ha in a catchment of 280 km2 amounts to less than half a percent, even if it retained all the rainfall that falls on it. Of course additional tree coverage is good, for many reasons, but it should be situated in the upper reaches if its purpose is to reduce runoff. It cannot do this in floodplains.
Additional tree coverage is good, for many reasons, but it should be situated in the upper reaches if its purpose is to reduce runoff. It cannot do this in floodplains.
If the purpose is to provide a home for ‘large woody debris and leaky dams’ these would have to be managed very carefully if new problems are to be avoided. Indeed, I doubt whether this measure would be acceptable in many locations, for three reasons: First, man-made dams have to be constructed to extremely high standards because the risk caused by a failure is unacceptable. Whilst natural ‘leaky dams’ would clearly be on a small scale, the risk of failure, and in particular a ‘domino’ flood wave, would have to be very carefully considered. Second, one of the greatest causes of property flooding is the blockage of bridges by woody debris. Third, storing water behind dams, even if secure, will raise water levels upstream and therefore increase the area of floodplain. Surrounding landowners would have to accept this. And… even beavers lose their homes in severe floods!
Whilst perhaps less appealing, large scale improved agricultural land management is likely to have a greater benefit than tree planting. There is plenty of evidence that much of our farmland is compacted and suffers from soil erosion caused by heavy rainfall. This approach has the additional benefits of reducing sedimentation and chemical run-off.
If tree planting and large woody debris in floodplains is going to be a solution then the benefits will need to be demonstrated, and the risk understood, to a far greater extent.
The official water quality data speaks for itself and is an indictment. Major improvements were made, almost 50 years ago now, in the lower catchment but the overall standards are now falling. A catchment cannot be healthy without good water quality and so I consider this to be the most important issue.
The causes appear clear, being mainly agriculture and, to a lesser extent, sewage discharges (both treated and untreated). There are few nature-based solutions unless you include having a lower reliance on chemicals on the farm and in the home.
Improvement can only come from improved agricultural practice, brought about by education and incentive, and backed by more effective regulation.
The catchment still has much to offer but it has been, and could again be, better.
Over recent years I have seen the decline of species such as curlew, sand-martin, eels, lamprey and trout. I have also seen an increase in invasive species such as the signal crayfish and Himalayan balsam. Otters appear to have returned and new arrivals like the white and cattle egret are generally welcome as long as they don’t replace the heron.
A major, probably the major, remaining obstruction to fish movement is the weir at King’s Mill Cullompton. Migrating fish species find this obstruction (almost) impassable.
Some parts of the catchment are noticeably low in interest, in particular the Spratford Stream, including the Halberton Stream. This is largely because of poor water quality.
In general, my support is for targeted action against undesirable species and for habitat improvement for desirable species. Put simply, “If we look after the rivers, the fish will look after themselves”. Fundamental to looking after our rivers is to have good water quality.
The Review provides an informative collection of the data and associated issues. Nature-based solutions can contribute to improvement, but only if they are complemented by more effective use of other measures and regulation, much of which already exist but is not being implemented. I look forward to seeing solutions, which will also need to be presented with clarity and rigour.
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