The effective discharge (Qe) and bankfull discharge (Qb) can equal each other and both have a return period approximately equal to the mean annual flood (MAF). This would be the normal condition for a hypothetical river in an equilibrium state.
There are four other conditions possible:
1) Qb frequent, Qe infrequent (Qe>Qb)
2) Qb infrequent, Qe frequent (Qb>Qe)
3) Qb and Qe both frequent (Qb and Qe < MAF)
4) Qb and Qe both infrequent (Qb and Qe > MAF)
Condition 1 represents streams with stable banks composed of relatively immobile sediment - an armoured channel with a low sediment supply, for instance.
Condition 2 represents what is probably a degraded channel, that has recently deepened itself, or that developed under a previous hydroclimatic regime, but is not armoured. Sediment moves through the channel frequently but the bank rarely overtops. It could also represent a fine gravel and sand bed channel with armoured banks (for instance, cut into glaciofluvial cobbles).
Condition 3 would likely be an actively aggrading glaciofluvial, meandering stream with bankfull discharge possible during any high-temperature melt event, or another similar condition
Condition 4 would be like condition 2 but with the additional constraint of condition 1 (low sediment supply). These would likely be the most stable channels.
