Concerned this plant is invasive and doesn't protect against soil erosion

Concerned this plant is invasive and doesn't protect against soil erosion

Observation - Concerned this plant is invasive and doesn't protect against soil erosion - Southern Africa. Description: This plant started coming up in spring 2015 (Sept/Oct). By Jan/Feb 2016 they had become very thick and quite tall. Now some of the plants are as long as 3meters. There are so many growing so close together. The plants have a very shallow roots system and

This plant started coming up in spring 2015 (Sept/Oct). By Jan/Feb 2016 they had become very thick and quite tall. Now some of the plants are as long as 3meters. There are so many growing so close together. The plants have a very shallow roots system and with a big tug you can get the 2 meter tall ones out the ground. This doesn't seem ideal for soil erosion protection on a river bank. When it rains hard, some of the plants are underwater (about 40cm deep with a big rain).

They are very straight, narrow plants with a maroon coloured flower. The flower looks like it will become many tiny seeds.