Table of Contents
Volume 19. San Juan Sub-basin ...... 3 Geographic location ...... 3 Political and Administrative Boundary ...... 4 Land Cover ...... 6 Sub-basin Characterization and Properties...... 8 Drainage Network ...... 8 Sub-sub basin Properties ...... 10 Water Quantity ...... 11 Streamflow ...... 11 Water Balance ...... 12
LIST OF FIGURES Figure 19-1 Geographical Map ...... 3 Figure 19-2 Political Map ...... 6 Figure 19-3 Land Cover Map ...... 7 Figure 19-4 Drainage Map ...... 9 Figure 19-5 Sub-sub basin Map of San Juan Sub-basin ...... 10 Figure 19-6 Streamflow, 1990-2004 ...... 12 Figure 19-7 Water Balances based on model simulation, 1990-2004 ...... 13
LIST OF TABLES Table 19-1 Geographic extent ...... 4 Table 19-2 Municipalities and Barangays Covered ...... 4 Table 19-3 Population Distribution by Municipality, 2007 ...... 5 Table 19-4 Area Distribution of Land Cover ...... 7 Table 19-5 Some Relief Features and Other Geo-Morphological Parameters ...... 8 Table 19-6 San Juan Sub-sub basin properties ...... 11 Table 19-7 Streamflow Data, 1990-2004 ...... 11 Table 19-8 Yearly Water Balances based on model simulation (units in mm) ...... 12
Technical writer Engr. Erwin Kim P. Mercado, LLDA-PDMED
Technical editors Ms. Adelina C. Santos-Borja Engr. Emiterio C. Hernandez Officer-In-Charge Officer- In Charge Resource Management and Development Officer Project Development Management and Evaluation Division
Map production Mr. Neil V. Varcas, LLDA-PDMED
Volume 19. San Juan Sub-basin
Geographic location The San Juan Sub-basin is located at the southwestern portion of the Laguna de Bay Basin. The sub-basin covers the barangays of two (2) municipalities and three (3) cities, namely: Municipality of Sto. Tomas, Municipality of Malvar, Calamba City, Tanauan City and Lipa City. It also covers small portions of the barangays which belong to Los Baños, Calauan, Bay, and Alaminos. However, these areas do not have significant impact on the San Juan Sub-basin, hence; these areas were not included in this report. Figure 19-1 illustrates the geographic location and boundary of the San Juan sub-basin in the Laguna de Bay.
Source: LLDA GIS Figure 19-1 Geographical Map As to the coordinates of the five municipalities and cities within the San Juan Sub-basin, Calamba City is located at latitude 14°13' N, and longitude 121°10' E while Malvar’s geographical coordinates are 1403’ N and 12110’ E. Sto. Tomas on the other hand, is located at 1405 N, 12110’55”E. Tanauan City is located within 14°5’ N and 121°6’ E at the North- Eastern part of Batangas. As for Lipa City in Batangas, it is located in latitude 13o 57’ N and longitude 121o 10’ E. The geographic extent of the sub-basin is presented in Table 19-1.
Its total land area is about 20,421.391 hectares. The City of Tanauan and Sto. Tomas have the largest land areas within the sub-basin while Malvar has the least. However, in terms of the number of barangays covered by the sub-basin, Sto. Tomas has the greatest proportion (100 percent), followed by Calamba City (90.74 percent), Tanauan City (58.33 percent), Malvar (40 percent) and Lipa City (4.17 percent).
Table 19-1 Geographic extent CORNERS NORTHING (UTM) EASTING (UTM) Upper Left 1545663.50000 309923.09375 Upper Right 1545663.50000 288606.83957 Lower Right 1573821.50000 288606.83957 Lower Left 1573821.50000 309923.09375 Source: LLDA GIS
Political and Administrative Boundary The San Juan sub-basin is one of the largest sub-basins within the Laguna de Bay region (Figure 19-2). It covers 123 barangays located in 10 municipalities and cities coming from the three provinces of Laguna, Batangas and Cavite. Four of which (Alaminos, Bay, Calamba and Los Baños) are situated in Laguna, other five (Tanauan, Lipa, Malvar, Sto. Tomas and Talisay) in Batangas while the remaining in the Province of Cavite (Tagaytay City). Table 19-2 shows the detailed figures on the jurisdiction of the sub-basin. Sto. Tomas is the largest municipality accounting for almost 44% (8,879.32 hectares) of the total area of the sub-basin. In view of barangays covered, Calamba City and Tanauan City have the most with 33 both, followed by Sto. Tomas with 30.
Table 19-2 Municipalities and Barangays Covered MUNICIPALITY/CITY NUMBER OF BARANGAYS AREA (ha) PERCENTAGE (%) Calamba City 33 2795.588 13.68% Tanauan City 33 5232.298 25.61% Sto. Tomas 30 8879.320 43.45% Malvar 7 1438.652 7.04% Lipa City 8 1960.992 9.60% Los Baños 5 57.142 0.28% Bay 1 0.35 0.00% Alaminos 4 39.97 0.20% Tagaytay 1 15.807 0.08% Talisay 1 13.979 0.07% TOTAL 123 20,434.10 100% Source: LLDA GIS Based on the 2007 Census of Population by the National Statistics Office, the total population within the San Juan sub-basin is estimated at 376,555. Number of inhabitants residing in the barangays within the territories of Lipa City, Tagaytay City and Talisay, Batangas were not considered in the total number of population within the sub-basin since the same are not under the jurisdiction of LLDA
Tanauan City, having the largest area percentage making up the sub-basin, also shared the highest number of inhabitants with 38% or 142,537. On the other hand, Los Baños contributes the least number of population at 1,479 (0.39%). Average growth rate was determined at 2.94%. Table 19-3 shows the detailed population data of each municipalities as well as the annual growth rate.
Table 19-3 Population Distribution by Municipality, 2007 MUNICIPALITY POPULATION ANNUAL GROWTH RATE (%) Calamba City 65,931.42 3.48 Tanauan City 142,537 2.69 Sto. Tomas 113,105 4.82 Malvar 41,730 3.42 Los Baños 1,479.47 2.57 Bay 2,081.00 2.07 Alaminos 9,691.20 1.55 TOTAL 376,555 National Statistics Office, 2007 Census of Population
Source: LLDA GIS Figure 19-2 Political Map
Land Cover Based on the land cover validation undertaken by LLDA PDMED, grassland, brushland and plantation occupy vast areas of the sub-basin having 30%, 26% and 19% of the total area, respectively. Table 19-4 shows the land cover distribution in the sub-basin of San Juan while Figure 19-3 shows the land cover map.
Table 19-4 Area Distribution of Land Cover LAND COVER AREA (ha) PERCENTAGE Urban 885.01 4.33% Forest 928.81 4.55% Arable 3341.08 16.36% Plantation 3827.55 18.74% Grassland 6049.20 29.62% Brushland 5351.24 26.20% Marsh 21.90 0.11% Unclassified 9.47 0.05% Cloud 8.95 0.04% TOTAL 20423.21 100.00% Source: LLDA GIS
Source: LLDA GIS Figure 19-3 Land Cover Map
Sub-basin Characterization and Properties
Drainage Network The drainage map of the San Juan Sub-basin is shown in Figure 19-4 while the important watershed characteristics and geomorphological features are in Table 19-5.
Table 19-5 Some Relief Features and Other Geo-Morphological Parameters PARAMETERS VALUES Area (ha) 20421.39 Perimeter (m) 96254.684 Total number of streams 31 Total length of streams (m) 196913.593 Stream Density (stream/ha) 0.0015 Drainage Density (m/ha) 9.6425 Constance of Channel Maintenance (ha/m) 0.1037 Length of Overland Flow (m) 4.8213 Source: LLDA GIS
Source: LLDA GIS Figure 19-4 Drainage Map
Sub-sub basin Properties
Source: LLDA GIS Figure 19-5 Sub-sub basin Map of San Juan Sub-basin
Table 19-6 San Juan Sub-sub basin properties SUB-SUB BASIN NAME AREA (Ha) PERIMETER (m) SSB-18A 7985.704 108295.963 SSB-18B 997.966 18844.909 SSB-18C 561.348 15217.305 SSB-18D 1321.432 19667.447 SSB-18D 0.343 2271.800 SSB-18E 972.934 13621.702 SSB-18F 594.739 14860.921 SSB-18G 1716.078 29161.803 SSB-18H 971.126 26425.894 SSB-18I 1419.672 27654.548 SSB-18J 515.686 20892.736 SSB-18K 209.367 8152.229 SSB-18L 582.157 18288.979 SSB-18M 400.268 16590.883 SSB-18N 1158.686 16705.088 SSB-18O 1014.229 25789.770 Source: LLDA GIS
Water Quantity
Streamflow
The yearly average streamflow of the San Juan sub-basin from Year 1990 to Year 2004 is illustrated in Table 19-7 and Figure 19-6 wherein the highest peak flow can be observed in Years 1999 and 2000 with almost 10.67 m3/sec and 11.31 m3/sec, respectively. On the other hand, the lowest was recorded in Years 1997 (4.58 m3/sec) and 2003 (4.95 m3/sec).
Table 19-7 Streamflow Data, 1990-2004 YEAR STREAMFLOW 1990 10.66455 1991 7.582415 1992 7.464764 1993 8.64358 1994 5.937204 1995 8.135792 1996 6.915276 1997 4.584825 1998 7.647382 1999 10.66522 2000 11.31476 2001 6.45754 2002 5.818203 2003 4.958207 2004 5.570332 Source: LLDA PDMED
Source: LLDA PDMED Figure 19-6 Streamflow, 1990-2004
Water Balance
The Sacramento Soil Moisture Accounting (SAC SMA) Hydrologic Model is used to simulate watershed rainfall-runoff relationship and to generate the long-term water balance of the 24 sub- basins of Laguna de Bay. The SAC SMA accounts for all water entering, stored in, and leaving a drainage basin. Though many parameters are used in this water balance accounting process, precipitation has the main impact on runoff.
For San Juan River Basin, the long term water balances of the basin based on the hydrologic simulation is shown in the table below. The 15-year average would show that 47.56% of the total rainfall becomes surface run-off, and about 37.22% of rainfall is lost as actual evapotranspiration. The base flow component of the total run-off is quite minimal, with only about 14.17% of rainfall, while the remaining 1.06% is stored as soil moisture and contributes to groundwater aquifer (Figure 19-7).
Table 19-8 Yearly Water Balances based on model simulation (units in mm) ACTUAL EVAPO- DIRECT CHANGE IN YEAR RAINFALL BASEFLOW TRANSPIRATION RUNOFF STORAGE 1990 2,300 721 1,278 397 (96) 1991 1,938 732 937 247 22 1992 1,889 682 948 229 31 1993 2,115 598 1,108 272 138 1994 1,557 751 656 268 (119) 1995 2,107 639 1,055 260 153 1996 1,782 740 871 222 (51) 1997 1,331 705 508 211 (93) 1998 2,035 616 979 181 259 1999 2,423 786 1,212 422 3 2000 2,552 802 1,326 376 48 2001 1,769 799 714 303 (47) ACTUAL EVAPO- DIRECT CHANGE IN YEAR RAINFALL BASEFLOW TRANSPIRATION RUNOFF STORAGE 2002 1,583 662 696 220 4 2003 1,438 668 591 190 (11) 2004 1,625 685 648 232 60 AVERAGE 1,896 706 902 269 20 Source: LLDA PDMED
Source: LLDA PDMED Figure 19-7 Water Balances based on model simulation, 1990-2004