MEM LCL CTLR DESCRIBED GAR AND DELAYED DEP EVENTS; CLAIMING CRDA OPS WERE A CAUSAL FACTOR FOR BOTH; ADDING; MINIMAL CRDA TRAINING MINIMAL GIVEN.

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RWY 18L WAS CLOSED. I WAS WORKING LCL 2 POS IN THE TWR; CTLING TFC LNDG AND DEPARTING RWY 18C. THERE WAS A LCL CTL 3 OPEN WORKING TFC LNDG RWY 27; ALSO. APCH WAS USING CONVERGING RWY DISPLAY AID (CRDA) TO SEQUENCE ACFT TO RWY 18C AND RWY 27. A DC9 WAS ON APCH TO RWY 18C AND A CRJ-200 WAS ON APCH TO RWY 27; SEQUENCED TO ARRIVE BEHIND DC9. FOR THE ENTIRE PUSH; THE RWY 27 FINAL CTLR HAD VECTORED HIS ACFT CLOSE TO THE TARGET CONVERGING RWY DISPLAY AID PROVIDED; SO I COULD NOT MAKE THE DECISION THAT THE OP WAS NOT GOING TO WORK UNTIL THE LAST SECOND. IN THIS INSTANCE; I INSTRUCTED DC9 TO GO AROUND ON LESS THAN A 1/2 MI FINAL BECAUSE CRJ-200 WAS OVER THE APCH END OF RWY 27. WHILE COORDINATING THE RE-SEQUENCE OF DC9; I NOTICED A DEP FLT PROGRESS STRIP SITTING IN MY BAY FOR RWY 18C. A CRJ-700 HAD BEEN WAITING AT THE APCH END FOR APPROX 8-10 MINS. MY ATTN HAD BEEN SO FOCUSED ON THE CONVERGING RWY DISPLAY AID OPS FOR THE ARR ACFT THAT I HADN'T NOTICED THE ACFT WAITING FOR DEP. I WISH THAT EITHER THE GND CTLR WHO HAD TAXIED THE ACFT OR THE PLT OF THE ACFT HAD CALLED TO LET ME KNOW THEY WERE THERE. DUE TO INSUFFICIENT TRAINING ON THE CONVERGING RWY DISPLAY AID OP; THIS OP IS NOT VERY CONSISTENT AND; THEREFORE; NOT VERY SAFE AT MEM.