Engineering Hydrology (hydrologic Equation)

“Hydrologic Equation”
-The Change in Storage shouldn’t be Negative-
The hydrologic equation states that change in storage of a reservoir is the difference between the inflow & the outflow to that reservoir.
  Change in storage= I-O
I = Total Inflow
O = Total Outflow
∆S = Change in Storage during a given Time in a given Area
As I’m saying that the change in storage should not be negative, so the reason behind that; output from the system depends on
-the nature of input
As this heading is purely showing that the output depends only on the input that’s why the outflow should never be greater than the inflow. For example 100m3 water is entering under the area of catchment than there are no chances that more than 100m3 outflow from that area of catchment. Is it possible in case of dam, that there is 1M m3 water is present and the out flow is 1.1M m3 ? definitely NO. that’s why the change in storage shouldn’t be negative.
-the physical laws involved
According to N.M Awan; this equation is merely a description of the laws of the mass conservation - no water is creating into the system that make outflow more than the inflow- So the outflow is under the limit of inflow.
-the nature of the system
The nature of the system is actually the nature of the area of the catchment that is in practical is a Dam, Pound or any kind of depression even a cylinder. That leads that presence of water or any incoming source of water is treated as inflow and the outgoing water is treated as outflow from that area of catchment. For example if we are taking a cylinder(constant area) how we calculate the inflow? Actually we are taking its depth. How we calculate the outflow? also in depth. And how we calculate the change in storage?  Definitely the difference of that depth. Is it possible that outflow increase the depth of water in that container? No, not at all, that’s why outflow is under the limit of inflow and the change in storage shouldn’t be negative.
Comments:
The problem is that you are thinking that outflow can increase from the inflow as the outflow can also be taking place through that storage water.
I think we are dealing with the area of catchment and that storage water is also the inflow, as we measure the depth of that water storage which includes in inflow, as I explained above outflow can’t be increase the depth of that storage. That’s why change in storage shouldn’t be negative.