Water from a land area of 4.730 km2 discharges into Eyjafjörður with rivers. This region extends from Siglunes in the west to Gjögurtá in the east. Many rivers run down the valleys and end in Eyjafjörður. In the west the small river Ólafsfjarðará runs into Ólafsfjörður. South of that is Svarfaðardalur ond its secondary valleys and the rivers from the valleys gather into the river Svarfaðardalsá that flows into Eyjafjörður just south of the town of Dalvík.

From Hörgárdalur comes the river Hörgá and from Glerárdalur above Akureyri the river Glerá originates and discharges into Eyjafjörður through Akureyri. The largest rivers are still unmentioned and one of them the river Eyjafjarðará enters the head of fjord and outside it there are extensive mudflats. The valley that the river runs through has the same name as the fjord and it is very long or about 60 km. The river Fnjóská discharges the fjord in Dalsmynni. It is one of the longest rivers in Iceland about 120 km.

Measurements of the discharge of the rivers into Eyjafjörður are rather scarce but the National Energy Authority has made some measurements in the rivers Fnjóská, Eyjafjarðará and Bægisá that is a small tributary of the river Öxnadalsá that unites with Hörgá further down. The total annual discharge to the fjord can be estimated from these data and precipitation data from weather observations and it has been estimated to be 188 m3/s on average over time. If this flow over a whole year is spread over the fjord it would be 17 m thick, which is among the highest in Icelandic fjords.

In addition, about 0.5 m of precipitation should be added to this. The mean precipitation in Grímsey is 678 mm and 474 mm in Akureyri. Precipitation is greatest in autumn and remains relatively high during the winter, but has a minimum in May and June.

Floods occur in the rivers in spring when the snow is melting. In September small maxima in the discharge are common, due to increased precipitation that quickly shows up in the rivers. During the winter the discharge is relatively small. In 1992 the spring flood came in late May and early June. It started rather abruptly peaking at about 230 m3/s. In 1993 the spring flood did not occur until the latter part of June due to the cold spring. The maximum discharge was then 240 m3/s. This flood was however preceded by several smaller floods. The maximum flow is about ten times the average flow of the river. The flow in the river Fnjoská is slightly more even than in Eyjafjarðará, especially during the summer months. The explanation is that Fnjoská river is much longer and the flow is evened out on the way to the sea.

Steingrímur Jónsson

Úrkoma á Akureyri og í Grímsey á árunum 1931-1960. Meðalársúrkoma yfir allt tímabilið er sýnd í sviga (gögn frá Veðurstofu Íslands). Úrkoma á Akureyri og í Grímsey á árunum 1931-1960. Meðalársúrkoma yfir allt tímabilið er sýnd í sviga (gögn frá Veðurstofu Íslands).

Ferskvatnsrennsli í nokkrum ám í Eyjafirði (gögn frá Hafrannsóknastofnuninni). Ferskvatnsrennsli í nokkrum ám í Eyjafirði (gögn frá Hafrannsóknastofnuninni).