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HEC SUBROUTINE BLFLO SPECiAl BRIDGE ROUTINE LOW FLOW CONTROL (TRAPEZOIDAL CHANNEL) .... CALQJLATE CRITICAL DEPTH OUTSIDE BRlpGE CONSTRICTlOII 5090* . CALQJLATE CRITICAL DEPTH WITHIN BRIDGE CONSTRICTION 5170 \ CALQJLATE M)MENTUM WITHIN BRIDGE FOR CRITICAL OEPTH S170 t YES I IS SUBCRITICAL FLOW ASSlJMEO INSTEAD OF SUPERCRITlCAL FLOW? I NO I 5200 I 1 IS MI)jENTUM IN CONSTRICTION BASEO ON OOWNSTREAM DEPTH IS MOMENTUM IN CONSTRICTIOft BASED 011 UPSTREAM OEPTH GREATER THAN CRITICAL MOMENTUM WITHIN BRIDGE? GREATER THAN CRITICAL MOMENTUM AT BRIOGf! 5210 521lO YR<; . ~ NO 1Yl>S I NI CALQJLATE UPSTREA~ WATER WATER DEPTH IN BRI DGE~ SOLVE FOR DEPTH I CLASS CI WATER DEPTH IN BRIDGE~ SURFACE EL, BY YARNELL CRITICAL; CLASS B FLOW IN BRIDGE ~'IlICH HAS MOMEN- CRITICAL: CLASS B FLOW ENERGY EQ. FOR CLASS A -- 5225 lUM EQUAL T\) MWoENTUK WI TH- -- 5270 FLOW T I N CON STR I CT I ON BASEO ON \ 5220 UPSTREAM DEPTH SOLVE FOR NEW DO\mSTREAH 5300-5_10, 5260 SOLVE FOR NEW UPSTREAM SOLVE FOR DEPTH IN BRIDGE OEPTH (LESS THAN CRill CAL) ~ DEPTH (ABOVE CRITICAL) WN I CH HAS HOMENTUH EQUAL BASED ON CRITICAL MOMENTUM BASEO 011 CR I TI CAL MD- T\) MOMENTUM WITHIN CON- AT BRIDGE SOLVE FOR OOWNSTREAM OEPTH MEllTUM AT BRIOGE STRICTIOH BASED OH OOWH- 5300-5UO. 5226 (LESS THAN CRITICAL) WNICH 5300-51110, 52BO STREAM OEPTH . HAS MOMEN TIJH WI TH I H CON- T 5300-5~10, 51160 STR I CT I ON BASEO ON IJf'STREAH I PRINT NOTE: DOWN STREAM DEPTH PRINT NOTE: UPSTREAM DEPTH I S , NOT 5300-5.10. Sll30 ELEVATIOft IS fRETURN TO MAIN PROGRAM HYDRAUL I C JIIHP OCCVRS OOIIN- NOT NEW BACKWATER STREAM REQl/IRED 8226 8290 \ I SOLVE FOR UPSTREAM DEPTH \RETURN 10 MAIN PROGRAM I SOLVE RlR DOWNSTREAM (ABOVE CRITICAL! BASED ON DEPTH (BElOW CRITICAL) CRITICAL MOMENTUM AT BRIOGE BASEO 011 CR! TICAL HD- 5300-5_10, 5_20 MDTUM ~JogmGE 5 -5_10. Sll30 *Numbers refer to statement numbers in source program. Figure 2. General Program Logic For Low Flow Calculations (Reference g)