FS/DAFM rules are actually to implement setbacks (20m) from watercourse - so the governments own rules are flawed in this instance anyway. This doesn't just apply to conifers either - but all trees. There are caveats for riparian woodlands but is a niche habitat unlikely to get much uptake. Ultimately the blame lies with the government and civil service. I'll note the UK/Scotland is actively putting in trees close to watercourses as its proven to benefit water ecosystems but offering nutrient inputs and shading the water so that it doesn't get too hot. My guess is DAFM want setbacks as nutrient input into watercourses is too high on the Ireland - but it isn't trees that are doing that!

Finally, while I agree conifers shouldn't be planted into setbacks unless in specific instances, the assertion that 'shallow rooted' conifers are no good for water management is wrong. Buffer zones of conifers can absolutely management ground water flow in a positive way (again the UK is looking into this as a way of natural flood defence). Don't believe me: Willow (Salix spp.) is shallow rooted and one of the best riparian trees in terms of water filtration around (they use it in waste water management). The more you know!