Explanation:

The correct answer is option 'D' - Slope-area method. Let's understand why the slope-area method is not a direct stream flow determination technique.

Slope-Area Method:
The slope-area method is a commonly used indirect method for determining stream flow in open channels. It involves measuring the cross-sectional area of the channel and the slope of the water surface. By applying the principles of conservation of mass and energy, the flow rate can be calculated. However, it is not considered a direct stream flow determination technique because it relies on measurements and calculations rather than direct measurement of the flow.

Direct Stream Flow Determination Techniques:
Direct stream flow determination techniques involve directly measuring the flow rate of water in a stream or channel. These techniques provide more accurate and precise measurements compared to indirect methods. Some of the commonly used direct stream flow determination techniques include:

1. Dilution Method:
The dilution method involves adding a known quantity of a tracer (such as a dye or salt) to the stream and measuring the change in concentration downstream. By knowing the initial concentration of the tracer and the rate of dilution, the flow rate can be calculated.

2. Ultrasonic Method:
The ultrasonic method utilizes ultrasonic sensors to measure the velocity of the water flow. By combining the velocity measurements with cross-sectional area measurements, the flow rate can be determined.

3. Area-Velocity Method:
The area-velocity method involves measuring the cross-sectional area of the channel and the velocity of the water flow. By multiplying the area and velocity, the flow rate can be calculated.

These direct stream flow determination techniques provide accurate and reliable measurements, making them suitable for various applications in water resources engineering, hydrology, and environmental studies.

Conclusion:
The slope-area method is not considered a direct stream flow determination technique because it relies on measurements and calculations rather than direct measurement of the flow. The dilution method, ultrasonic method, and area-velocity method are examples of direct stream flow determination techniques that provide more accurate and precise measurements.