That depth above which total integrated photosynthetic rate equals total integrated respiration of photosynthesizers.

depth of water for which specific energy is a minimum.  esign Flow - projected flow through a watercourse which will recur with a stated frequency. The projected flow for a given frequency is calculated using statistical analysis of peak flow data or using hydrologic analysis techniques.

(Depth at which specific energy is a minimum) - The depth of water in a conduit at which under certain other conditions the maximum flow will occur.  These other conditions are the conduit is on the critical slope with the water flowing at its critical velocity and there is an adequate supply of water.  The depth of water flowing in an open channel or a conduit partially filled, for which the velocity head equals one-half the hydraulic mean depth.