Possibly half way round near Turton Reservoir, streams running into it. some of which will be fairly large and OK I think.Might be easier if you go on the old route along side the res rather than past the strawberry duck etc
If you get really desperate after Darwen Tower vary the route to top down to pub and visitor centre slightly further north than where you cross the road at Slipper Lowe on entry into Roddlesworth woods. Once you get over Great Hill and down to White coppice you should kind some streams especially as you go near some of the reservoirs