The average daily discharge can change greatly. It has been, over long periods, averaged as about 300 cubic meters per second. It can be as low as 140 and as high as 1800, depending on the velocity of the water arriving from upstream and the weirs west of Arnhem, which control the water taken in. These control the Pannerdens Kanaal, the sole inflow (shared with the Nederrijn). As a lowland river in which velocity decreases, the IJssel
meanders. Some bends (and spurs of land,
hank) have been cut off by man such as near
Rheden and
Doesburg, reducing the length from 146 km to 125 km, but not as radically as the
Meuse nor
Great Ouse. Deposition of sediment to form islands in the outside of bends has been curtailed since the late nineteenth century.
The IJssel as a Rhine distributary Since the connection between the Rhine and IJssel was dug, the Rhine became the main contributor to the flow of the IJssel – a small fraction of the former's flow makes up the upper IJssel. Various tributaries add a little or much water to the flow of the IJssel, such as the
Berkel and
Schipbeek streams from relatively local
precipitation. The IJssel, if accepted as a branch of the
Rhine-Meuse-Scheldt delta, is the only one that takes up tributary rivers rather than giving rise to distributaries. It has no contact with the Meuse, nor Scheldt, nor their resultant watercourses. In the last few miles of the river's run, near the city of
Kampen, distributaries form, resulting in a quite small
delta. Some of these have been dammed up to lower the risk of
flooding. Some have silted up. Others flow without interruption. Most of the damming-up was done before 1932, when the Zuiderzee was turned into the freshwater
IJsselmeer lake. The whole delta had been prone to flooding in times of northwestern
gales, pushing back the saline Zuiderzee water into the delta. The modern-day names of the delta branches are, west to east, the: • Keteldiep • Kattendiep • Noorddiep (local drainage ditch only) • Ganzendiep • Goot Of these, the first-stated two are the main navigations. The Noorddiep has been stopped up at both ends. Another branch, De Garste, had already completely silted up by the middle of the nineteenth century. Until about 1900, the Ganzendiep up to the Goot fork was known as IJssel proper The IJssel, now mainly a Rhine branch as to its water, has retained most of the character of a distinct river in its own right. It has its own tributaries and, as to the Old IJssel (
Oude IJssel), a former
headstream.
Tributaries and connecting canals The following
canals, long ditches and
tributary streams feed the IJssel, in downstream order: •
Apeldoorns Kanaal (west) near the
town of
Dieren • river
Oude IJssel (east) at the
city of
Doesburg • the
Berkel stream (east) at the city of
Zutphen • the
Twentekanaal (east) between Zutphen and the village of
Eefde (
municipality of
Gorssel) • the
Schipbeek stream (east) near the city of
Deventer • the
Grift stream (west) at the town of
Hattem; its lower reaches have been
channelised to form the mouth of the
Griftkanaal • the
Willemsvaart canal (east) at the city of
Zwolle • the
Zwolle-IJsselkanaal (east) near Zwolle == River crossings ==