 being located on top of a natural hill site whose slope directs the flow in an upward direction, so that {HEAD ~ the said angular relationship} between the helicoid axes and {TAIL ~ the flow vector} is secured on account of the chosen location 
being located on top of a natural hill site whose slope directs the flow in an upward direction , so that { HEAD ~ the said angular relationship } between the helicoid axes and { TAIL ~ the flow vector } is secured on account of the chosen location
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH