MEM LCL CTLR DESCRIBED INCIDENT INVOLVING SIMULTANEOUS APCH PROCS TO RWY 36L-R WHEN SEPARATION WAS LOST AND GAR WAS REQUIRED.

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WHILE WORKING THE LCL CTL #1 (LC1) POS LAST WK; I EXPERIENCED SEVERAL INSTANCES WHERE SEPARATION WAS GOING TO BE LOST IN THE FINAL APCH COURSE TO RWY 36R. UNFORTUNATELY; I WAS UNABLE TO WRITE THE CALL SIGNS DOWN DUE TO HOW BUSY THE POS WAS AT THE TIME OF THESE INCIDENTS. MEM WAS IN A N CONFIGN DURING OUR NOON ARR PUSH. WE WERE LNDG RWYS 36L AND 36R. FINAL MONITORS WERE UP AND OPERATIONAL. DUE TO THE LOW CEILINGS AND VISIBILITY; I WAS UNABLE TO SEE ANY RWY 36L ARRS UNTIL THEY WERE APPROX 1/2 MI FINAL. VISUAL SEPARATION COULD NOT BE APPLIED BTWN SUCCESSIVE ARRS; AND I WAS REQUIRED TO ASK ARRIVING ACFT TO 'EXPEDITE' OFF OF THE RWY; OR TO 'TURN R ASAP' IN ORDER TO ALLOW THE NEXT ARR TO LAND WITHOUT INCIDENT. AS THE ARR PUSH PROGRESSED; SEVERAL HVY JETS WERE SEQUENCED TO MY RWY. WIND RPTS ON THE SURFACE INDICATED 10 KT HEADWINDS; AND THIS INCREASED SLIGHTLY FOR EVERY 1000 FT BASED ON PIREPS. COMPRESSION WAS A SERIOUS ISSUE; AS WAS EVIDENT BY OBSERVING HOW 5 MI RADAR SEPARATION AT THE STEP-DOWN FIXES WOULD DECREASE TO 2.5-3.0 MI AT THE THRESHOLD WITH LIKE-TYPE LARGE ACFT. WHEN THE HVY JETS STARTED TO CHK ONTO MY FREQ WITH 4-6 MI OF SPACING DEPENDING ON THE TYPE OF ACFT THAT WAS FOLLOWING THE HVY; I KNEW THAT THE ASSIGNED SPDS AND SPACING WOULD NOT WORK. MEM LCL PROCS MANDATE THAT THE FINAL MONITORS ARE RESPONSIBLE FOR THE SEPARATION ON FINAL UNTIL 1 MI FROM THE RWY OR UNTIL THE TWR CAN PROVIDE VISUAL SEPARATION. THERE WERE AT LEAST 4 INSTANCES WHERE SEPARATION WAS IN PROCESS OF BEING LOST; AND I ASKED THE FOLLOWING ACFT TO 'SAY SPD' IN AN EFFORT TO GIVE THE FINAL MONITOR A HINT OF WHAT WAS HAPPENING. THE FINAL MONITOR ALWAYS TOOK THE HINT; AND BEGAN REDUCING THE SPD OF THE TRAILING ACFT; BUT IN THE END; IT WAS ALWAYS TOO LATE. ON 2 INSTANCES I TOOK THE INITIATIVE AND SIMPLY CANCELED THE APCH CLRNC OF THE ACFT THAT WAS FOLLOWING THE HVY JET; AND THEN ASKED THE CAB COORDINATOR TO COORDINATE A HDG AND ALT WITH THE APPROPRIATE RADAR SECTOR DOWNSTAIRS.