Collapsible dam

Claim 1

A WATER COURSE CHANNEL SECTION AND COLLAPSIBLE DAM COMBINATION COMPRISING: A DAM CHANNEL SECTION IN A WATER COURSE, SAID CHANNEL SECTION EMBODYING A GENERALLY TRANSVERSELY FLAT BOTTOM, SAID BOTTOM INCLUDING A TRANSVERSE PORTION OF SUBSTANTIALLY HARD NONYIELDING MATERIAL HAVING A PLANE SURFACE FOR MOUNTING A COLLAPSIBLE ENVELOPE THEREON, AN ELONGATED SUBSTANTIALLY FLUID IMPERVIOUS ENVELOPE EXTENDING TRANSVERSELY OF SAID CHANNEL SECTION, THE ENVELOPE BEING FORMED FROM A SHEET FOLDED OVER WITH FREE EDGES COINCIDENT FORMING AN UPSTREAM LEADING EDGE PORTION SEATING UPON THE MOUNTING SURFACE, MEANS CLAMPING SAID LEADING EDGE PORTION UPON SAID MOUNTING SURFACE IN INTIMATE CONTACT THEREWITH ALONG THE ENTIRE LENGTH OF SAID LEADING EDGE PORTION, SAID ENVELOPE TRAILING DOWNSTREAM FROM SAID EDGE PORTION MOUNTING, FLUID INLET AND OUTLET MEANS CONNECTED TO SAID ENVELOPE WHEREBY FLUID MAY BE PASSED INTO SAID ENVELOPE TO INFLATE IT, AND OUT OF SAID ENVELOPE TO DEFLATE IT, SAID ENVELOPE WHEN INFLATED PROVIDING A DAM IN OPERATIVE RELATION TO A BODY OF WATER UPTREAM OF SAID ENVELOPE AND WHEN DEFLECTED COLLAPSING TO LAY GENERALLY FLAT IN INOPERATIVE RELATION TO SUCH WATER WHICH WILL NOT MATERIALLY DECREASE THE FLOW OF WATER BUT REMAINING PERMANENTLY INSTALLED IN SAID WATER COURSE, THE CLAMPING MOUNTING OF SAID LEADING EDGE PORTION ON SAID MOUNTING SURFACE BEING SUFFICIENTLY WATERTIGHT SUBSTANTIALLY TO PREVENT WATER FROM FLOWING BETWEEN SAID LEADING EDGE PORTION OF THE ENVELOPE AND SAID MOUNTING SURFACE.