YEAR       MONTH       BHini        FLQQ        FLQR       BHend       FOUTQ       WITHD      RTN_FW        BALR
BHini:	Water stored in river channel at the begin of the month (10^6m^3)
FLQQ :	Base flow from groundwater (10^6m^3)
FLQR :	Surface flow (10^6m^3)
BHend:	Water stored in river channel at the end of the month (10^6m^3) 
FOUTQ:	Discharge (10^6m^3) 
WITHD:	Water withdraw from the river (10^6m^3)
RTN_FW: Return flow because of irrigation (10^6m^3)
RIVBAL =BHini + FLQQ + FLQR - BHend - FOUTQ - WITHD + RTN_FW