TERTIARY IRRIGATION CONVEYANCE SYSTEMS (WATERCOURSES) IN THE INDUS BASIN LOSE 30 TO 50 PERCENT OF THEIR FLOW. WATERCOURSE SYSTEMS WERE STUDIED IN DEPTH BY PONDING AND INFLOW-OUTFLOW METHODS TO DETERMINE FUNCTIONAL RELATIONSHIPS BETWEEN SEVERAL MEASUREABLE PARAMETERS AND THE LOSS RATES. THE OBJECTIVE WAS TO DETERMINE SIMPLE DESIGN CHANGES THAT ARE LOW COST AND CAN LEAD TO INCREASED CONVEYANCE EFFICIENCIES IN THE EARTHEN CHANNELS. STATISTICAL ANALYSIS OF THE COLLECTED DATA INDICATED THAT: 1. WATERCOURSE LOSS RATES (1PS/100M) INCREASE WITH, BUT SLIGHTLY LESS THAN PROPORTIONAL TO, THE USUAL FLOW RATE IN THE CHANNEL; 2. LOSS RATES ARE LOWER IN MORE OFTEN USED CHANNELS; 3. LOSS RATES ARE HIGHER IN ELEVATED CHANNELS; 4. LOSS RATES ARE VERY SENSITIVE TO CHANGES IN FLOW DEPTHS, AND THUS INCREASE WITH UPWARD FLUCTUATIONS IN FLOW RATES OR ROUGHNESS COEFFICIENTS; AND 5. INTAKE RATES INTO UPPER BANK SOILS ARE VERY HIGH AND ARE APPARENTLY CAUSED BY EXTENSIVE RODENT AND INSECT BURROWS INSIDE THE BANKS. A WATERCOURSE LOSS MODEL WAS CONSTRUCTED BASED ON THE DERIVED RELATIONSHIPS, AND WAS APPLIED TO SEVERAL PRACTICAL WATERCOURSE DESIGN ALTERNATIVES.