Sounds a wonderful concept …The idea of a runnel is to provide the sound of water without actually seeing the water or if you do see it it’s on a occasional basis…. I have built several in gardens and invariably they have a lawn edge interspersed with planting. The variation in sound is provided by marginals in the runnel creating a backlog so you achieve natural heights and falls. I have never seen or used any man made blockages as nature quickly provided the necessary blockages. The necessary fall is actually minimal bearing in mind that the pump is doing most of the work.. And also remember that a runnel is based on an agricultural drainage ditch although in the romantic sense…So consider a Robert Hardy painting in an appropriate setting not much wider than a foot so that it is easy to step across. Depth is gernerally one to two feet max…Will dig up photo’s if you are interested..Water fall is constant and shallow. Best of luck…Sounds fun..
