What is the height of water above the crest of the weir if it is measured at 2.5 ft?

When measuring the height of water above the crest of a weir, it is the actual depth of the water that directly contributes to the weir's discharge and hydraulic performance. If the measurement shows that the height of the water is 2.5 ft above the crest, this directly indicates that the water level is precisely at 2.5 ft, which affects the flow characteristics over the weir.

Understanding this is essential in water resource engineering, as the height of the water can influence flow rates and design calculations for managing water systems. Given that the height is measured and stated to be 2.5 ft, this simply confirms the direct measurement and reflects the state of the water level concerning the weir's structure. This relates to how weir equations such as the broad-crested or sharp-crested weir equations are applied, which take into account the height of water for predicting flow rates or designing weirs for specific applications.

This foundational understanding helps clarify that the measurement is indeed indicative of the actual height, ensuring the design and calculations align with the observed operating conditions.