Stream/waterfall

Marguerite is right - moss needs cool, damp and shady conditions to grow. Ferns also need shade - I can't think of any that enjoy sunny places. Why not more grasses for now, like the lovely one in the photo - is it a Stipa? Then try low-growing plants like Creeping Jenny, small yellow flowers - it's 'Lysimachia nummulaaaria 'Aurea' - or 'Convululus sabatius' mauve flowers, or Persicaria affinis . In the spring there's lots of choice - Aubrieta, Saponaria ocymoides, Iberis sempervirens, Alyssum saxatile, Phlox subulata etc. Once you have these established your stream will look so pretty!

PUT SOME GRITTY SOIL INBETWEEN YOUR ROCKS. PLANT NEPETA - LAMIUM(WHITE NANCY), CAMPANULA, mERCADONIA. WATER REGULARLY FOR FIRST MONTH UNTIL IT ALL GETS ESTABLISHED.

Would love to see some up-to-date pictures of this stream.
Did you find a way of disguising the concrete?