HYDROLOGIC AND WATER RESOURCES EVALUATIONS FOR SG. LUI WATERSHED 1.0 Introduction The Sg. Lui watershed is the upper part of Langat River Basin, in the state of Selangor which located approximately 20 km west of Kuala Lumpur city between longitudes 101 52 to 101 59 and latitudes 3 6 to 3 13. This watershed drains the western flank of Gunung Hitam (1210 m) and is a major tributary of the Langat River. The preparation of this given task is based on the Water Resources Publication No. 7 (WRP7) and Water Resources Publication No. 9 (WRP9) that published by Department of Irrigation and Drainage (DID), Malaysia. WRP7 is the representative basin report for the year 1971/72 to 1973/74, whereas WRP9 presents report for the year 1974/75 to 1975/76. 2.0 Physical Characteristics of Sg. Lui Watershed In the evaluation of physical characteristic of a watershed, it is good to have the following data layers that can be prepared using GIS. (a) Map delineation (b) Slope assessment (both channel and watershed) (c) Drainage characteristics (d) Land cover (e) Soil types (f) Basin geology However, until this report stage only map delineation, channel and watershed slopes, and drainage data layers are prepared which based on regular digital topographic maps. Special up to date maps should be obtained from the related government agency to present land cover, soil types and basin geology of the watershed. The connection of these data layers for evaluation of any hydrological or hydrogeological study can be extended from the schematic representation shown in Figure 1. 1
Data layers Sub-areas Slopes Drainage Land cover Soil types Evaluation of watershed s physical characteristic Figure 1. The Use of Data Layers in Evaluation of Watershed s Physical Characteristic 2.1 Map Delineation With the advent of current computers, geographic data can be stored in the form of grid cells by using Digital Elevation Models (DEMs). Typically, these grid cells have a resolution of 30 meters and elevation intervals of 1 meter. Using a DEM within a Geographical Information System (GIS), the Digital Terrain Analysis (DTA) can be performed such as slopes, flow lengths and delineate watershed boundaries and stream networks. The ArcView GIS version 3.1 is used to facilitate the map delineation which is started from compilation of the digital topographic maps obtained from the library of UPM. The maps that consist of required layers are converted from.dwg to.dxf files using the AutoCAD. All the.dxf files are then used in the ArcView GIS to create the.shp files, and develop the Triangulated Irregular Network (TIN) surfaces and Digital Terrain Model (DTM). Several hydrologic interpretations from the Digital Elevation Model (DEM) data are performed by using the following Terrain Preprocessing tool. The visualizations of each result are attached in APPENDIX A. (a) Fill Sinks (b) Flow Direction (c) Flow Accumulation (d) Stream Definition 2
(e) (f) (g) (h) (i) (j) Stream Segmentation Watershed Delineation Watershed Polygon Processing Stream Segment Processing Watershed Aggregation Full Preprocessing Setup The basin and locality map for Sg. Lui with rainfall and river gaging stations are shown in Figure 2. This map can be used to compare the result from Flow Accumulation operation given in Figure 3 which seen to be reasonably acceptable. From the Full Preprocessing Setup, many small sub-areas are created for the watershed as shown in Figure 4 which are depend on the inputs from previous operation. Some of the sub-areas can be combined to form an appropriate sub-area for each stream. Aggregation of these sub-areas that is provided through Watershed Aggregation processing is given in Figure 5 which sometimes shows inappropriate form of subareas. A further manually aggregation procedure can be performed using Geoprocessing Wizard tool to produce a better merging of sub-areas according to user s defined sub-areas. Figure 2. Sg. Lui Watershed 3
Figure 3. Result from the Flow Accumulation Process Figure 4. Sub-areas for Sg. Lui Watershed 4
Figure 5. Aggregation of Sub-areas The area and perimeter of each sub-area can be obtained using Tabulate Area tool in View menus as shown in Figures 6 to 8. These menus also provide Derive Slope tool to show the surface slope of watershed as illustrated in Figure 9. Finally by using River Length and River Slope tools in Basin Characteristics menu, the tabulated characteristics extracted for streams in Figure 10 are summarized in Figure 11. From the results shown above, GIS has successfully demonstrates most of the watershed s physical characteristics. In addition of that, some further estimation of watershed s slope and shape as a whole are also presented in this report. As given in the WRP7 and WRP9, the total area of Sg. Lui watershed is 68.1 km 2 and its maximum length is 12 km. The estimated length of main stream is 14 km and its elevation ranged from 80 m to 578 m. Therefore, estimation for the whole watershed slope is as follows: - Difference in elevation, Length of the flow path, E 578 80 498 L 14 km E 498 m Watershed slope, S 0. 0356 L 1000 m 14 km 1 km m 5
The watershed has a small upstream area and enlarged gradually towards downstream which can be categorized as concentrated shape (Bedient et. al., 2008). The perimeter, P and length to the center of area, L ca is estimated to be 34 km and 8.682 km, respectively. Then, the watershed parameters that reflect basin shape (McCuen, 2005) are calculated as shown below. (a) Shape factor, L LL 8.6992 5.3947 3. 173 (b) watershed in miles. Circularity ratio, l F c ca P 0.3 34.5 4 A 4 68.1 0.3 0 0.5 A 68.1 (c) Circularity ratio, R 0. 740 2 34 c Ao 2 1.162 2 A 2 68.1 (d) Elongation ratio, Re 0. 621 L 15 m 0.5 0.5, where L is the length of the Figure 6. Area and Perimeter of Downstream Sub-Area 6
Figure 7. Area and Perimeter of Intermediate Sub-Area Figure 8. Area and Perimeter of Upstream Sub-Area 7
Figure 9. Derived Slope of the Watershed Figure 10. Identified River for Slope Calculation 8
Figure 11. Tabulated Lengths, Slopes, Upstream and Downstream Elevations of the River 3.0 Estimation of Precipitation and Streamflow for Sg. Lui Watershed The preliminary estimation of streamflow and precipitation values in this watershed is shown in Table 1. These include range for average annual precipitation over the basin, discharge per square kilometer of basin area and percentage of annual basin flow occurring in each month. Table 1. Preliminary Estimation Range for annual precipitation (mm) 1550-3450 Annual discharge per unit area (m 3 /s / sq. km) 0.026 Monthly flow as a percentage of mean annual flow (%) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 7.5 6.0 5.8 8.4 9.1 7.5 6.4 6.3 8.2 10.8 13.0 10.9 9
4.0 Monthly Analysis of Sg. Lui Streamflow There is only one gaging site is available for Sg. Lui which is station 3118455 located at longitude 101 52 and latitude 3 11. This station provides the period of record from the year 1965 to 2000 and the streamflow is recorded according to calendar years (January December). The mean annual discharge and discharge per unit area for this station are 1.77 m 3 /s and 0.026 m 3 /s / sq. km, respectively. The example of this calculation is shown in Figure 12. The simple statistics for the data set are performed such as mean, standard deviation, maximum value and minimum value. These can be simply calculated by using functions in Excel which are AVERAGE, STDEV, MAX and MIN for the range of data set as shown in Figure 13. Various plots of monthly data with simple statistics included as given in Figure 14 also can be visualized in Figures 15 and 16. Figure 12. Calculation of Mean Annual Discharge and Discharge per Unit Area 10
Figure 13. Simple Statistics on Monthly Data Figure 14. Simple Statistics Data for Various Plots 11
Figure 15. Various Plots with Simple Statistics Included Figure 16. Various Plots with Simple Statistics Included 12
Mean monthly discharge for the period of record is defined as the average flow for each month for the entire period of record. The plot of mean monthly flows shown in Figure 17 illustrates the yearly streamflow pattern of the stream. The stream seems to have large flows in wet season from October to December and has low flows in dry season of February and March. The pattern of surface runoff and baseflow also can be analyzed from Figures 15 and 16. Some of the flow data for 1972/73 to 1973/74 are given in WRP7 which include peak discharges, low flows, baseflow recession and baseflow component of runoff. The same analysis of flows can be performed for streamflow data from 1965 to 2000 if further characterization of the hydrograph pattern is required. Figure 17. Mean Monthly Discharge Versus Month 13
5.0 Ratio of Mean Monthly Discharge to Mean Annual Discharge Mean monthly flow (MMQ) as a ratio of mean annual flow (MAQ) and as a percentage of mean annual flow show the ratio or percentage of the annual flow occurs in each month of the year. The example of calculation is below and a complete calculated data is given in Figure 18. Mean monthly flow = MMQ Mean annual flow = MAQ MMQ Ratio of MMQ to MAQ = MAQ MMQ Percentage of MMQ to MAQ = 100 MAQ When interested in seasonal aspects of flow at a site or when working with more than one site, it is useful to be able to normalize values for comparison. For example, if two different sites and comparison of the monthly discharge values is required, it would be useful to have a normalized value to compare. For normalization purposes, monthly flow values can be viewed as percentages of annual flow values. The plot of normalized monthly data as shown in Figures 19 and 20 have the same distribution as mean monthly flow in Figure 17. Figure 18. Mean Monthly Discharge as a Ratio or Percentage to Mean Annual Discharge 14
Figure 19. Ratio of Mean Monthly Discharge Mean Annual Discharge Figure 20. Percentage of Mean Monthly Discharge to Mean Annual Discharge 15
References Bedient, P. B., Huber, W. C. and Vieux, B. E. (2008). Hydrology and Floodplain Analysis (4 th ed.). USA: Prentice Hall. Geospatial Hydrologic Modelling Extension HEC-GeoHMS. User s Manual (Version 1.1). Hydrologic Engineering Center, US Army Corps. of Engineers: California, 2003. Mc Cuen, R. H. (2005). Hydrologic Analysis and Design (3 rd ed.). US: Prentice Hall. Sg. Lui Representative Basin Report No. 1 for 1971/72 to 1973/74, Water Resources Publication No. 7. Department of Irrigation and Drainage: Kuala Lumpur, 1977. Sg. Lui Representative Basin Report No. 2 for 1974/75 to 1975/76, Water Resources Publication No. 7. Department of Irrigation and Drainage: Kuala Lumpur, 1978. Viessman, W. J. and Lewis, G. L. (2003). Introduction to Hydrology (5 th ed.). US: Prentice Hall. 16