I can’t see the useful document you refer to but would be interested to see it as we are currently improving our paperwork to ensure our projects are CDM compliant.
I recently attended a CDM training course and just wanted to clarify that CDM applies to all construction projects regardless of size. A project being ‘notifiable’ to HSE does only apply to larger projects (30 days/500 person days) but all construction projects fall under CDM and there are legal duties under this for the ‘client’, the ‘designer’ and the ‘contractor’, of which the Rivers Trust could be any one or all of these.
Leaky dams may not class as construction if they are simply forestry operations of felling a tree across the watercourse but if a ‘structure’ is created the work will fall under CDM.
In answer to your original question I haven’t heard of any issues around CDM with small projects and a simple record of information exchange and risk assessment for the work is likely to be sufficient.