Many nations have examples of these type studies or water data collection agencies. In USA, many examples can be found with US Geological Survey stream gauging and water data network, and US Forest Service Hydrological Experiment Stations, addressing many climate and physiographic, as well as land use issues Typically using small catchment or drainage area studies, employing paired watersheds or other sampling approaches when appropriate. Sampling river systems includes need for watershed data on geology, soils, land use, pollution sources, etc. to design a meaningful and valid sampling approach to help meet your desired intent for data to help address your questions. Collaboration with hydrology and other technical specialists including GIS to help compile information is helpful. Experienced hydrology and related scientists also helpful for review, advice, etc. , but if unavailable, there is ample research and publications that can provide helpful examples.
It is an important question pertaining to river or reservoir system reliability.
Stream flow and other variables are characterized by variability and uncertainty- the system must be evaluated from a risk perspective.
The study of Risk perspective is actually termed as reliability studies. in other words.It is a measure of the level of dependability at which water supply and such other environmental requirements can be met.
River system reliability studies are based on simulation model considering water use requirements and past stream flow.
Various reliability indices can then be formulated from simulation like Rv, Rp i.e. Volume reliability and period reliability. Rv is the ratio of volume of water supplied v the volume needed V expressed as percentage. Rp is % of time that a specified water use requirements met .