A discordant system or pattern does not correlate to the topography and geology of the area. Discordant drainage patterns are classified into two main types: antecedent and superimposed, while anteposition drainage patterns combine the two. In antecedent drainage, a river's vertical incision ability matches that of land uplift due to tectonic forces. Superimposed drainage develops differently: initially, a drainage system develops on a surface composed of 'younger' rocks, but due to denudative activities this surface of younger rocks is removed and the river continues to flow over a seemingly new surface, but one in fact made up of rocks of old geological formation. Dendritic drainage patterns Dendritic drainage pattern Dendritic drainage systems (from Greek , dendrites, "of or like a tree") are not straight and are the most common form of  drainage system. In this, there are many sub-tributaries (analogous to the twigs of a tree), which merge into tributaries of the main river (the branches and the trunk of the tree, respectively). They are seen to feed a river channel that matches and is strongly accordant to the overriding gradient of the land. Truly dendritic systems form in V-shaped valleys; as a result, the rock types must be quite  impervious and non-porous. Trellis drainage pattern The geometry of a trellis drainage system is similar to that of a common garden trellis. Along a strike valley, smaller tributaries feed into from the steep slopes of mountain sides . These tributaries enter the main river about perpendicular, causing a trellis-like appearance of the system. They form where hard and soft formations exist on both banks of the main river, and are reflective of height, accentuated by erosion. Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America and in the north part of Trinidad.Ritter, Michael E., The Physical Environment: an Introduction to Physical Geography. 2006 Rectangular drainage pattern Rectangular drainage develops on rocks that are of approximately uniform resistance to erosion, but which have two directions of jointing at approximately right angles or 90 degrees. The joints are usually less resistant to erosion than the bulk rock so erosion tends to preferentially open the joints and streams eventually develop along the joints. The result is a stream system in which streams consist mainly of straight line segments with right angle bends and tributaries join larger streams at right angles. This pattern can be found with the Arun River in Nepal.
A discordant system or pattern does not correlate to the topography and geology of the area. Discordant drainage patterns are classified into two main types: antecedent and superimposed, while ante position drainage patterns combine the two. In antecedent drainage, a river's vertical incision ability matches that of land uplift due to tectonic forces. Superimposed drainage develops differently: initially, a drainage system develops on a surface composed of 'younger' rocks, but due to denudation activities this surface of younger rocks is removed and the river continues to flow over a seemingly new surface, but one in fact made up of rocks of old geological formation. Dendritic drainage patterns Dendritic drainage pattern Dendritic drainage systems (from Greek , dendrites, "of or like a tree") are not straight and are the most common form of the drainage system. In this, there are many sub-tributaries (analogous to the twigs of a tree), which merge into tributaries of the main river (the branches and the trunk of the tree, respectively). They are seen to feed a river channel that matches and is strongly accordant to the overriding gradient of the land. Truly dendritic systems form in V-shaped valleys; as a result, the rock types must be quite obviously impervious and non-porous. Trellis drainage pattern The geometry of a trellis drainage system is similar to that of a common garden trellis. Along a strike valley, smaller tributaries feed into the steep slopes of mountainsides . These tributaries enter the main river about perpendicular, causing a trellis-like appearance of the system. They form where hard and soft formations exist on both banks of the main river, and are reflective of height, accentuated by erosion. Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America and in the north part of Trinidad.Ritter, Michael E., The Physical Environment: an Introduction to Physical Geography. 2006 Rectangular drainage pattern Rectangular drainage develops on rocks that are of approximately uniform resistance to erosion, but which have two directions of jointing at approximately right angles or 90 degrees. The joints are usually less resistant to erosion than the bulk rock so erosion tends to preferentially open the joints and streams eventually develop along the joints. The result is a stream system in which streams consist mainly of straight line segments with right-angle bends and tributaries join larger streams at right angles. This pattern can be found with the Arun River in Nepal.
R
anteposition
ante position
R
denudative
denudation
A
the
A
obviously
D
from
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mountain sides
mountainsides
R
right angle
right-angle