Erren River originates in Neimen, Kaohsiung. Its main stream is 61.2 kilometers long, and its basin occupies an area of 339.2 square kilometers. The meander of Erren River is at the upper and middle section of the river where the mudstone region that crosses Tianliao, Neimen and Longci in Tainan City is located. The typical heavy rainfall in this region results in a special meandering channel. The channel curvature increases as the meander develops, causing the river to cut through the neck of the meander to form a straight channel. The meander is then cut off and becomes an oxbow lake at the lower section, while the small hills at the middle section turn into meander cores.