Stream Flow fluctuations and Land Use Changes

in Bandung Basin

Ida Narulita

Research Center for Geotechnology

Indonesian Institutes of Sciences (LIPI)

Introduction Study area Methods Results

Analyses conclusion

BackgroundWithin several last decades floods and droughts happened almost every year, and getting more and more severe.On the other hand, some areas pose the problems of water scarcity.

CHANGE IN HYDROLOGIC REGIME OF THE WATER SHED

Causes:

Rainfall pattern changeLand Use / Land Cover Change

FOTO: SOBIRIN 2005

Research objectives:

To gain a better understanding on the impact significance of changes of rainfall and land Use/land cover patterns on the watershed hydrologic regime.

Principal methods:

Parameters

Correlation analysis between rainfall depth and land use/land cover density to hydrologic regime

Rainfall: monthly depth (mm) Land use/Land cover density: indexed by run off

coefficient for each type of Land use/Land cover according to CN-NRCS methode

Hydrologic regime: Baseflow and highflow discharges changes

Data Monthly Rainfall Data from 19 stations spread

over the study area (Bandung Basin) for the period of 1986-2010 (25 years).

Hydrograph for the period 1980 - 2009 recorded at Nanjung AWLR station, the outlet of the Upper Citarum watershed.

Land use map of 1976, 1994, 1999, 2001, 2004 and 2008 of Bandung basin derived from satellite imageries (Landsat MSS, ETM satellite images +7 and Aster).

Study Area : Bandung Basin

Distribution of rainfall stations and discharge station at Bandung Basin

Btsdas_Citarum_0605_polylineut Legend

drainage Legend

Posisi_St_Bdg Legend

Stas_Nanjung Legend

Batas DasLine

Waduk Saguling

Anak SungaiBadan Sungai

Stas. Pencatat Hujan

Stasiun Pencatat Luah Nanjung

Methods

Monthly Isohyet Mapping:Daily rainfall data collectionData series correction by Double Mass

Curve.Selection of representative stations to

determine regression equations between rainfall and elevation

isohyet map construction using the obtained regression equations

Method

Regression Equation between Monthly Rainfall and Elevation of Northern Slope of

Bandung Basin

Method

Digital Topography Map

Method

Satellite Imagery Processing for land cover mapping: case studi

Bandung Basin

Method

Administration Administration BoundaryBoundary

Watershed Watershed BoundaryBoundary

4 Scene Satellite Imagery covering Bandung Basin

Landcover density index: Land use types area * Run off coeff icient

Run Off Coefficient derived from CN-NRCS graph

Method

Landuse Type CN % RO/RF Factor

Forest 60.5 0.6 0.14 0.28

Plantation 69 0.67 0.19 0.38

Dryland 78.5 0.78 0.27 0.34

Wetland 70 0.72 0.22 0.44

Settlement 93 0.93 0.425 0.85

Stream Flow Separation

Recursive digital filter equation:

q1 = αqi-1+ β (1 + α) (Qi –Qi-1)

And : qB1 = Q1 – q1

Q1 = TF (Total Flow) series

q1 = HF (high flow) series

qB1 = BF (base flow) series

i = time index (day)

α, β, = separator parameters (α = 0.95; β = 0.5)

Method

Result Curve of Base Flow - High Flow Separation

at Nanjung 1980

Method

Result

Monthly Isohyet Maps

Result

Januari 1986 Pebruari 1986 Mei 1986

Juli 1986 Nopember 1986 Desember 1986

Variability of Average Monthly Rainfall at Bandung Basin (1986 -2010)

Result

Landuse Changes in Bandung Basin

Result

The Changes of forest area pattern in Bandung Basin occurred in 1976, 1994, 1999, 2001 and 2008

1976 1994 1999 2001 2008

Landuse Changes in Bandung Basin

Result

The Changes pattern of plantation area in Bandung Basin occurred in 1976, 1994, 1999, 2001 and 2008

1976 1994 1999 2001 2008

Landuse Changes in Bandung Basin

Result

The Changes pattern of upland field in Bandung Basin occurred in 1976, 1994, 1999, 2001 and 2008

1976 1994 1999 2001 2008

Landuse Changes in Bandung Basin

Result

The Changes pattern of settlements in Bandung Basin occurred in 1976, 1994, 1999, 2001 and 2008

1976 1994 1999 2001 2008

Landuse Changes in Bandung Basin

Result

The Changes pattern of paddy field in Bandung Basin occurred in 1976, 1994, 1999, 2001 and 2008

1976 1994 1999 2001 2008

Landuse (Land Cover) at Bandung Basin (1976 – 2008)

Result

Total Landuse/Landcover Index of Bandung Basin (1976 – 2008)

Result

Slow rate Sharp rate

Fast rate

Recapitulation of Streamflow separation

result

Result

Stream Flow Separation

Result

Streamflow discharge

Result

The Diagram of Landuse /Landcover Index, High Flow, Base Flow and Average Monthly Rainfall Depth

Result

Conclusion Landuse/landcover changes appear since 1994 with maximum decrease of vegetation cover density

rate happened in the period of 1998 to 2001. In the period of 2001 to 2008, vegetation cover density continuously decreased at a fast rate. During 1976 – 2008, land use changes in Bandung basin were decreasing forests (16 %), plantations (8%) and paddy fields (13.4%) and increasing upland fields (17 %) and settlements (21%).

Annual rainfall fluctuation is relatively constant, with 6 – 10 yearly variation. Monthly rainfall fluctuation shows strong increase in amplitude, especially after 2004.

Prior to 2003, base flow and high flow curves fluctuated according to the rainfall, however since 2003 the base flow curve shows a decreasing trend while the high flow curve shows an increasing trend.

Constant Base Flow decrease and/or High Flow increase appear after rapidly changes of the vegetational cover at 2003. This indicates that the hydrologic regime is influenced by the landuse change rather than by the rainfall fluctuation. More significant BF decrease and HF increase appear after 2006, likely enhanced by rainfall intensity increase

Conclusion

Research Question

Does land use changes influence rainfall pattern?

Which one, between land cover and rainfall fluctuation , affects more hydrologic regime?

Next Question