ABSTRACT

The perpetual transformation of instable river banks in the Kathmandu-Valley caused by lateral and depth erosion leads to an enormous loss of fertile soil and endangers the urban infrastrucure.

By means of an analysis of the riverine morphology in the Kathmandu-Valley the author attempts to establish an appropriate method for the evaluation of rivers. One of the objectives of the procedure is the estimation of the stability of river banks.
The work is based on investigations of rivers in the Kathmandu-Valley with special reference to the Bagmati.

The thesis consists essentially of two parts:

• a: The documentation of the riverine morphogenesis.
• b: The description of the inventory and evaluation method.

The description of Nepal and the Kathmandu-Valley emphasizes relevant geographical criteria which have a most important impact upon the riverine morphology.
The actual analysis of the riverine morphology in the Kathmandu- Valley reveals that the extensive alluvium, the low drop of the rivers and the extreme precipitation during the monsoon favours the lateral erosion of the river banks and leads to meandering rivers.
Next to geological and climatical factors it is above all the human being who influences the outer appearence of rivers and creeks.
The author distinguishes direct and indirect human influences on the stability of the river banks. Different forms of erosion are the results of various human influences.

An adequate method of inventory is designed in order to record the above mentioned factors. The procedure of the inventory is based upon selected methods used in German-speaking countries which the author describes in general terms.

The inventory is based on two principales:

• a: The division of the rivers in homogeneous segments.
• b: In order to standardize the documentation and to minimize the individual subjectivity the author defines nominations which can be used as a multiple choice system for the description of the rivers.

This is done by a five page standard form.
In addition, the author suggests the mapping of relevant structural elements such as erosion or vegetation etc.
Erosion and vegetation are the criteria for the evaluation of the bank stability.
Next to these criteria, the geology and the sinuosity (the ratio between the thalweg length and the air-line distance) are taken into consideration to judge the potential risk of erosion.
The condition of 25 river segments of the Bagmati with a total length of 31.1 km are illustrated in a graphic and a table.