Basinal and Planform Characteristics of the Kodku and the Godavari Rivers, Kathmandu, Central Nepal

Bulletin of the Department of Geology

Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 15, 2012, pp. 15–22

Basinal and planform characteristics of the Kodku and the Godavari Rivers, Kathmandu, Central Nepal

*Naresh Kazi Tamrakar and Ramita Bajracharya Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal

ABSTRACT

The rivers of the Kathmandu Basin are vulnerable to flash floods and disturbances caused by anthropogenic as well as climatic changes. Two southern tributaries of the Bagmati River: the Kodku and the Godavari Rivers, have been considered for their (i) watershed-scale geomorphic parameters such as relative relief, drainage texture and stream order, (ii) stretch- scale planform parameters such as sinuosity (K), meander belt width (Wblt), meander wavelength (Lm) and radius of curvature (Rc), and (ii) longitudinal profiles and slopes. Both Kodku and the Godavari Rivers are elongate basins with wide ranges of the watershed-scale parameters. The Godavari River is longer, larger and more sinuous compared to the Kodku River. The development of the patterns of the fifth order main stem stretches of both rivers with respect to the stream slopes, and asymmetric patterns of the meander loops indicate anomalous growth of the river stretches.

INTRODUCTION growing trend of urbanization, the rivers have been notably disturbed and instead the rivers have become Two major tributaries of the Bagmati River from threats to the settlement area, as they may unexpectedly the southeastern Bagmati Basin are the Kodku and the flood and inundate the floodplains. There were many Godavari Rivers (Fig. 1). These rivers have a typical flash flooding taking place in the Kodku River. In 1979 source of metasedimentary terrain composing Dhapakhel area was flooded, while in 1981, 2002 and dominantly of limestone of the Phulchoki Group 2007, Imadol and Gwarko areas were flooded and (Stöcklin, 1980). Rivers flow slightly northwestward damaged partially. In 2002 Gwarko area was inundated to contribute Bagmati River segments, i.e., the for more than a week. Similarly, the Godavari River Hanumante River by the Godavari River and the was flooded in 2006 and inundated and partially Manahara River by the Kodku River. Both the Kodku destroyed Balkot and Dharmeshwar areas. Therefore, and the Godavari Rivers are of fifth order with sinuous there is no doubt that the rivers of the Kathmandu valley, pattern. They have wide floodplains but narrow current including the Kodku and the Godavari Rivers bring meander belts. about flash flooding and partly destroy and inundate Urbanization in both the Godavari and the Kodku the cultivated lands and settlement areas. Rivers is very rapid at the present moment. Many civil Understanding the watershed scale relief and river colonies have been erected and roads have been extended system and planforms are crucial in the study of the to facilitate transportation. In this circumstance of river hydrology and the river related hazards (Tamrakar, *Corresponding author: 2004; Shrestha and Tamrakar, 2007; Shrestha and E-mail address: [email protected] Tamrakar, 2011). In light of this, the present study N. K. Tamrakar and R. Bajracharya/ Bulletin of the Department of Geology, Vol. 15, 2012, pp. 15–22

Relative relief CHINA Relative relief (RR), which is defined as the difference Kathmandu in height between the highest point and the lowest point NEPAL on the grid of a square kilometer, can be categorized into six classes as shown in Fig. 2. RR ranges from r e extremely high to low. It is extremely high in Majhgau iv INDIA R ti a and Badikhel, high in Muldol area, and moderate to m u n o moderately low in Taukhel Dhapakhel, Harisidhi and h 27 45’ is Khumaltar. It is low in Imadol area. RR diminishes B from the south to the north of the watershed. KATHMANDU

r Drainage texture e v

i r

R r

v The drainage texture (DT) is defined as the number

i e

v R

i of stream segment passes across per unit length within

a r

m u

a the square grid area (Horton, 1945). According to g

d o

a d

27 35’

B o

K drainage texture, basin can be classified as shown in 27 35’ G Fig. 3, into six categories ranging from extremely coarse to very fine (Singh, 1981). DT ranges from fine to very coarse (Fig. 3). It is fine in the southern mountain area Fig. 1 Location of study area such as Badikhel, moderate in Majhgau and Muldol, coarse in Bulu and Khatrigau, and very coarse in Taukhel, Harisidhi, Khumaltar and Imadol. Areas with bedrocks focuses on generation of watershed scale parameters and relatively high relief constitute relatively fine DT. and river planform parameters for the two southern DT is controlled by distribution of bedrocks and soft tributaries of the Bagmati River. sediments.

WATERSHED-SCALE PARAMETERS OF Stream order THE KODKU RIVER Stream ordering refers to the determination of the hierarchical position of a stream within a drainage basin. Watershed-scale parameters incorporate relative Stream order is defined as ‘a measure of the position relief, drainage texture and stream order for of a stream in the hierarchy of tributaries’ (Leopold, determination of which the spatial aspect of the whole Wolman and Miller, 1964). In this study, the drainage watershed is considered. order was determined using the method proposed by

Table 1: River morphological data of the Kodku and the Godavari Rivers Parameter Kodku River Godavari River 5th 4th 3rd 5th 4th 3rd Channel length (m) 11995.2 446.25 3427.2 13280.4 2266.415 1511.71 Belt length (m) 8996.4 339.15 3391.5 8192.27 1630.941 1445.99 Sinuosity 1.33 1.315 1.01 1.62 1.38 1.05 Meander belt width (m) 125.97 44.625 54.76 138.92 55.99 73.94 Meander wave length (m) 248.80 142.8 226.34 301.80 287.74 209.61 Radius of curvature (m) 65.56 60.018 55.89 90.15 110.89 103.93 Slope (m/m) 0.46 1.309 3.58 0.83 5.16 13.60 Average slope 2.58 4.18 *Sinuosity (K): S = sinuous (1.05 to 1.5); St = straight (<1.05) based on Leopold and Wolman (1957)

Study85024ShivapuriNStream Kmo 15’30’ area order Range Basinal and planform characteristics of the Kodku and the Godavari Rivers, Kathmandu, Central Nepal

85o20’00” 85o22’30” 85o20’00” 85o22’30” o o 27 40’00” 27 40’00” Imadol Imadol 15

1300 K 1300 K Datidol o Datidol d 30 o

o o 27 40’00” 27 40’00”

d k k u

Khumaltar u Khumaltar

Sitapakha R Sitapakha R 30 i v i v e e r r

Harisidhi Harisidhi N N

Dhapakhel Dhapakhel o o 27 37’30” 27 37’30” 0 500 1000 Km Thaiba 0 500 1000 Km 0.8 Thaiba 60 1340 1340 Khatrigau Khatrigau o o 27 37’30” 27 37’30”

Taukhel Taukhel

Tasinchok Khola Tasinchok Kh e ola Guhe G uh Bulu Bulu

r r e 0.4 v e 0.6 v 60 i 1540 i 1540

R R 120

u u

1440 k 1440 k

d d

o Badikhel Badikhel

K K o o 27 35’00” 27 35’00” Muldol Muldol 240 Majhgau Majhgau

1840 1840 1780 1780 1800 1800 o o 27 35’00” 27 35’00” Legend Legend Relative relief Major road Extremely high (>240) Drainage texture Major road Watershed boundary High (120–240) Very fine (0.0–0.2) Watershed boundary Sub-watershed boundary Moderate (60–120) Fine (0.2–0.4) Sub-watershed boundary Moderately low (30–60) Moderate (0.4–0.6) line defining equal drainage line defining equal relative Low ( 15–30) Coarse (0.6–0.8) 0.6 texture 60 relief Extremely low (0–15) Very coarse (>0.8) o 85o20’00” 85o22’30” 85 20’00” 85o22’30”

Fig. 2 A map showing relative relief in the Kodkhu watershed. Fig. 3 A map showing drainage texture in the Kodkhu watershed.

Strahler (1957; 1969). stream stretches for about 3427.2 m from Majhgau up The Kodku Watershed constitutes three sub- to the confluence of the Kodku River with the Guhe watersheds, of which the elongate Kodku sub-watershed Khola (Figs. 4 and 5; Table 1). The fourth order main is contributed by the Guhe sub-watershed from the east stem river stretches for 446.25 m up to Tasinchok where and the sub-watershed (Muldol area) from the southwest. it confluences with the major tributaries extending from The Kodku mainstem River is the fifth order river. There the Muldol sub-watershed. The fifth order main stem are altogether twenty-two 2nd order, six 3rd order and river stretches for about 11,995.2 m and finally two 4th order streams in the watershed. The third order contributes the Manahara River.

17 N. K. Tamrakar and R. Bajracharya/ Bulletin of the Department of Geology, Vol. 15, 2012, pp. 15–22

o 85o20’00” 85o22’30” 85 20’00” 85o22’30” o o 27 40’00” 27 40’00” Imadol Imadol

1300 1300 K K o Datidol o Datidol o d d o 27 40’00” 27 40’00”

k k u

Khumaltar u Khumaltar R

R Sitapakha Sitapakha

i i v v

e e

r r N

Harisidhi N Harisidhi 0 500 1000 Km

Dhapakhel 0 500 1000 Km Dhapakhel Fifth order o o stretch 27 37’30” 27 37’30” Thaiba Thaiba

1340 1340 Khatrigau Khatrigau Fourth order stretch o o 27 37’30” 27 37’30”

Taukhel Taukhel

Tasinchok K Tasinchok h e ho K ola G uh la Guh e Third order Bulu Bulu stretch

r e v r i 1540 e 1540 R v i

1440 1440 u

d k

Badikhel d Badikhel

o K

o o K

27 35’00” Muldol

27 35’00” Muldol Majhgau Majhgau

1840 1840 1780 1780 1800 1800 o o 27 35’00” 27 35’00” Legend Legend Stream order 1st order Major road Major road 2nd order Watershed boundary Watershed boundary 3rd order Sub-watershed boundary Sub-watershed boundary 4th 5th 1960 Elevation Meander belt width 85o20’00” 85o22’30” 85o20’00” 85o22’30”

Fig. 4 A map showing stream order in the Kodkhu watershed. Fig. 5 A map showing stream stretches and a meander belt of the Kodkhu River. PLANFORM PARAMETRES OF THE Meander wavelength (Lm) of the river is the distance KODKU RIVER between two successive crests or two successive trough

of the curved channel. Meander belt width (Wblt) is a Sinuosity, meander belt width, meander straight line between the crest of the bend to the crest wavelength and radius of curvature of the next bend lying downstream, or is the distance between lines defining the confinement of the lateral The planform geometry is well attributed by various boundaries of the channel. parameters: sinuosity, meander wavelength, meander belt width, and radius of curvature. Sinuosity (K) is the Radius of curvature (Rc) is the radius of a circle ratio of stream channel length to down-valley distance. drown through the apex of the bend and the two

18 Basinal and planform characteristics of the Kodku and the Godavari Rivers, Kathmandu, Central Nepal

2200 2nd order 2000 3rd order Knick point 1800 Knick 4th order 5th order point 1600

1400 Elevation (m) Guhe Khola 1200 0 2 4 6 8 10 12 14 16 Distance (km)

Fig. 6 A Longitudinal profile of the Kodku River. WATERSHED-SCALE PARAMETERS OF crossover midpoint of river, and is defined as the curved THE GODAVARI RIVER surface formed by the meandering stream channel. All these parameters were calculated from the topographic Relative relief map enlarge to 1:10,000-scale. The southern half of the Godavari watershed has The result of planform parameters are listed in Table extremely high relief (Fig. 7). The RR gradually 1. Sinuosity indices of the third, fourth and fifth order decreases towards NW. High RR is found in Godavari, main stem stretches of the Kodku River are 1.01, 1.32, from where RR diminishes through moderate to low in and 1.33, respectively showing sinuous nature according Taukhel and Lubhu, and becomes extremely low in to classification of Leopold and Wolman (1957). The Ikudol where the Godavari River confluences with the

Meander belt width (Wblt) of the fifth order main stem Hanumante River. Mountain slope with bedrocks show river is 125.97 m, while meander wavelength (Lm), and high RR whereas soft valley fill sediments represent Radius of curvature (Rc) are respectively, 248.80 m and low to extremely low RR. 65.56 m. Both Wblt and lm diminish from the 3rd to the 4th order stretches, and increases drastically in the Drainage texture 5th order stretch. Rc however remains almost similar. DT of the Godavari Watershed ranges from fine to very coarse (Fig. 8). It is fine in the central region of LONGITUDINAL PROFILE OF THE the watershed including Godavari, and becomes coarse to very coarse in both northwestward and southeastward KODKU RIVER regions. DT in extremely coarse in Lubhu and Godavari The longitudinal profile of the Kodku River reflects Bhanjyang (ridge) areas, and is moderate in Ikudol, its gradient throughout its length (Fig. 6). The slopes Ghimiregau and Kotdanda areas (Fig. 8). of the 5th, 4th and 3rd order stretches are 0.46 m/m, 1.31 m/m and 3.58 m/m, respectively. The average slope Stream order of the Kodku River is 2.58 m/m. Two distinct knick The Godavari Watershed comprises four sub- points, one close to the emergence of the 3rd order and watersheds; the Godavari sub-watershed, the Chisapani another close to the emergence of the 4th order streams, sub-watershed, Lubhu sub-watershed and the are present. The 3rd and 4th order main stem Kodku Charkhande sub-watershed. The latter three sub- River stretches have tendency to erode their channel. watersheds contribute laterally from the east to the

19 N. K. Tamrakar and R. Bajracharya/ Bulletin of the Department of Geology, Vol. 15, 2012, pp. 15–22

o 1288 85o22’30” 85o25’00” 1288 85 22’30” 85o25’00” o o 27 40’00” 27 40’00” N N o o 27 40’00” 27 40’00” Ikudol C Ikudol C h h 1310 a 1310 a rk 0 500 1000 2000 Km rkh 0 500 1000 2000 Km han and de e K 0.6 K ho ho 15 la 0.8 la Lubhu Lubhu 30 a a l 1330 60 l 1330 o o h Lu 120 h Lu

K b i K bh hu r u i K a K r v a h a h v o d o d a o D la o D l 240 a G h G h 0.8 a a m Damaitar m Damaitar i i l l o o 0.6 K K o h o h 27 37’30” Kotdanda 27 37’30” o Kotdanda o

l o l o a 27 37’30” a 27 37’30” Ghimiregaun Ghimiregaun 0.4

Taukhel Taukhel

a 240 la l o ho Kh K in in s rs r a a N 2140 N 2140

Godavari Godavari

a l 0.4 Ch o

a is Ch l a h is

o pa ap

ni K a

h K ni ho i Kho r K la l

o a o i

27 35’00” S a

27 35’00” S r u ug g v u

a o ur o re 27 35’00” 27 35’00” e a v K Kh ho

a ola d la d 1960

1960 o

o 0.6 G G 0.8

Godavari Godavari 2480 Bhanjyang 2480 Bhanjyang

Legend Legend Relative relief Extremely high (>240) Major road Drainage texture Major road High (120–240) Watershed boundary Very fine (0.0–0.2) Watershed boundary Moderate (60–120) Sub-watershed boundary Fine (0.2–0.4) Sub-watershed boundary Moderately low (30–60) line defining equal drainage Moderate (0.4–0.6) line defining equal relative Low ( 15–30) 240 relief 0.8 texture Coarse (0.6–0.8 Extremely low (0–15) Very coarse (>0.8) 85o22’30” 85o25’00” 85o22’30” 85o25’00”

Fig. 7 A map showing relative relief in the Godavari watershed. Fig. 8 A map showing drainage texture in the Godavari watershed.

elongate Godavari Watershed. The Godavari main stem River is a fifth order river. There are altogether fourty PLANFORM PARAMETRES OF THE 2nd order, fourteen 3rd order and four 4th order streams GODAVARI RIVER in the watershed. The third order stream stretches for about 1511.71 m from the Godavari Bhanjyang up to Sinuosity, meander belt width, meander the confluence with the third order tributary coming wavelength and radius of curvature from the eastern hill (Figs. 9 and 10; Table 1). The Sinuosity indices of the third, fourth and fifth order fourth order main stem river stretches for 2266.42 m main stem stretches of the Godavari River are 1.05, up to Godavari where it confluences with the Chisapani 1.38, and 1.62, respectively showing sinuous nature of Khola from the eastern hill. The fifth order main stem the 3rd and 4th order stretches, while meandering pattern river stretches for about 113280.4 m and finally of the 5th order main stem Godavari River, according contributes the Hanumante River.

20 Basinal and planform characteristics of the Kodku and the Godavari Rivers, Kathmandu, Central Nepal

o o 1288 85o22’30” 85o25’00” 1288 85 22’30” 85 25’00” o o 27 40’00” N 27 40’00” N o o 27 40’00” 27 40’00” Ikudol C Ikudol h Ch 1310 a 1310 a rkh 0 500 1000 2000 Km rkh 0 500 1000 2000 Km and and e e Kh Kh ola o la Lubhu Lubhu la o 1330 1330 h L K Lu u i b b r hu hu a a l o K K v h h a K o d h dava ri o G o o l Fifth order la G a D D stretch h h Damaitar a Damaitar a m m

i i l l o o o o 27 37’30” 27 37’30” K K Kotdanda h h o o o o 27 37’30” la Ghimiregaun 27 37’30” la Ghimiregaun

Taukhel Taukhel

240 la la o o Kh Kh in in rs rs a a 2140 N 2140 N

Godavari Godavari Fourth order

a l stretch o Ch

a i C l s h h a

isa o p

K p an

an h i K i i K h

K o r h la

o o o la i

S 27 35’00” a r 27 35’00” ug Su v u g r a u o e o r v e a K 27 35’00” ho 27 35’00” K a h d la ola

1960 o 1960 o

G Second G order stretch

Third order stretch Godavari 2480 Godavari 2480 Bhanjyang Bhanjyang Legend Stream order Legend 1st order Major road 2nd order Major road Watershed boundary 3rd order Watershed boundary Sub-watershed boundary 4th Sub-watershed boundary 5th Meander belt width 1960 Elevation 85o22’30” 85o25’00” 85o22’30” 85o25’00”

Fig. 9 A map showing stream order in the Godavari watershed. Fig. 10 A map showing stream stretches and a meander belt of the Godavari River. to classification of Leopold and Wolman (1957). The LONGITUDIANAL PROFILE OF THE Meander belt width (Wblt) of the fifth order main stem GODAVARI RIVER river is 138.92 m, while meander wavelength (Lm), and Radius of curvature (Rc) are respectively, 301.80 m and The longitudinal profile of the Godavari River shows 90.15 m. Wblt of the 5th order stretch is almost three concave type of slope (Fig. 11). The slopes of the 5th, times that of the 4th order stream. Lm gradually increases 4th and 3rd order stretches are 0.83 m/m, 5.16 m/m and from the 3rd order to the 5th order stretch. Rc however 13.60 m/m, respectively. The average slope of the diminishes from the 4th to the 5th order stretch. Godavari River is 4.18 m/m. The slope angles of all the stretches of the Godavari River are quite larger compared to those of the Kodku River.

21 N. K. Tamrakar and R. Bajracharya/ Bulletin of the Department of Geology, Vol. 15, 2012, pp. 15–22

2600 2nd order 2400

2200 3rd order

2000 4th order

5th order Dhamilo Khola Charkhande Khola 1800 Narsin Khola Lubhu Khola Elevation (m) 1600 Knick point 1400

1200 0 2 4 6 8 10 12 14 16 Distance (km)

Fig. 11 A Longitudinal profile of the Godavari River.

DISCUSSION AND CONCLUSION REFERENCES The Kodku and the Godavari Watersheds are elongate Horton, R.E., 1945. Erosional development of streams and and the former is contributed by two sub-watersheds, the streams and their drainage basins: Hydrological approach to quantitative geomorphology. Bulletin of and the latter by laterally the three sub-watersheds from the Geological Society of America, Vol. 56, pp. 275–370. the east. The Godavari River is longer and more sinuous http://dx.doi.org/10.1130/0016- than the Kodku River. In both rivers drainage texture 7606(1945)56[275:EDOSAT]2.0.CO;2 is fine to very coarse and relative relief is extremely Leopold, L.B. and M.G. Wolman, 1957. River channel high to low or extremely low, showing very contrasting pattern-braided, meandering and straight, USGS ranges of parameters, which are perhaps owing to the Professional Paper 282B. spatial variation of distribution of topographic highs Leopold, L.B., Wolman, M.G. and Miller, J.P., 1964. Fluvial and differences in stiffness in lithology. processes in Geomorphology, W.H. Freeman, San fransisco. The Kodku River falls under the sinuous river Shrestha, P. and Tamrakar, N.K., 2007. Streambank category whereas the Godavari River falls under the erodibility and lateral instability hazard in the Manahara meandering river category. Considering the slopes of River, Kathmandu Bsin, Nepal. Journ. Nepal Geol. the fifth order streams the sinuosity of these rivers show Soc., v. 35, pp. 55–66. Shrestha, P. and Tamrakar, N.K., 2011.Effects of human anomalous patterns because more sinuous stream of disturbances and climate on morphological changes of the Godavari River has been developed in the slope Bagmati River, central Nepal. Jour. Nepal. Geol. Soc., which is two times that of the Kodku River. Special Issue, v. 43, pp. 205–218. In terms of meander belt width, meander wavelength Singh, S., 1981. Estimation of drainage density, National Geographer, Vol. 16. No. 2, pp. 81–89. and radius of curvature, the Godavari River is larger Stöcklin, J., 1980. Geology of Nepal and its regional frame. compared to the Kodku River. In both rivers, the Jour. Geol. Soc. London, v. 137, pp. 1–34. planform parameters increase drastically when rivers http://dx.doi.org/10.1144/gsjgs.137.1.0001 emerge out as the fifth order main stem. Considering Strahler, A.N., 1957. Quantitative analysis of watershed the meander loops of both rivers, they show in most of geometry. Trans-American Geophysical Union, v. 38, the cases asymmetrical patterns, indicating frequent pp. 913–920. retardation and dilation. This is presumably due to http://dx.doi.org/10.1029/TR038i006p00913 disturbances (effects of pulses arising from flash Strahler, A.N., 1969. Physical Geography. 3rd edition, John Willey and Sons, Inc. New York. flooding, or any other natural and anthropogenic Tamrakar, N.K., 2004. Disturbances and instabilities in disturbances) to the rivers. the Bishnumati River corridor, Kathmandu basin, JUSAN, v.9, pp. Issue 16, pp. 7–18.