Annual Recurrence Interval (ARI) The average annual rate of occurrence of an event; it is equal to the 1/exceedance probability.
Annual daily peak flow The largest daily flow recorded in a year (m3/s).
Average daily peak flows Peak value of the daily discharge data, which are average values over 24 hours.
Confidence interval A range of values centred on the sample estimate that is known to contain the true value with a given degree of confidence.
Decision Support Framework (DSF) Mekong Basin Modelling and Knowledge Base, which comprises a suite of three integrated models representing at basin-scale, the surface water resource system of the Lower Mekong Basin (LMB), underpinned by a knowledge base of input and output data, and a range of analytical and reporting tools to facilitate assessment of potential flow changes on environmental and social conditions.
Dry season months Six calendar months from December to May (pending issue relating to implementation of Article 6A of the 1995 Mekong Agreement).
Environmental flow Environmental flow is the amount of water needed in a river to maintain healthy ecosystems.
Flood season months Four calendar months from July to October (relating to implementation of Article 6C of the 1995 Mekong Agreement).
Flow duration curve The flow duration curve is a plot of flows ranked from highest to lowest. The x axis is % of time equalled or exceeded and the y axis is flows (m3/s).
Historically severe drought and/or flood Daily flows exceed the 1:20 Annual Recurrence Interval of historically observed data at any selected station.
Monthly flow The sum of the daily flows in a month divided by the number of days in the month (m3/s). Identical to average flow for the month.
Moving average A method to smooth variations. The average is calculated, for example, over five years. For each year after this, the earliest value is dropped from the calculation and the most recent one is added in, again to make an average over five years; for example: 1988-93, 1989-94, and 1990-95. Also called running average.
Natural flows The term natural flows as used in Article 6 indeed means current flows under existing uses up to year 2000.
Probability of exceedance The statistical probability that an event will be exceeded, e.g. a 99 % probability of exceedance of daily flow means that the flow will exceed this value 99 of 100 days (on average).
Rating curve A graph of discharge versus stage; the corresponding discharge can be directly read from the graph when a water level is observed.
Threshold A value (or limit) of water level or discharge that will cause some action when crossed.
Wet season months Six calendar months from June to November (relating to implementation of Article 6B of the 1995 Mekong Agreement).
Flow frameworks Established thresholds for flows at each of the selected hydrological stations defining flow conditions at those stations, which are considered acceptable by the MRC Member Countries in relation to Article 6 of the 1995 Mekong Agreement, and/or which cause certain actions to be taken if transgressed.