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Home , Lumban, Pakil, Pangil, Tagaytay

Table of Contents

Volume 21. Biñan Sub-basin ...... 3 Geographic location ...... 3 Political and Administrative Boundary ...... 4 Land Cover ...... 6 Sub-basin Characterization and Properties...... 7 Drainage Network ...... 7 Sub-sub basin Properties ...... 10 Water Quantity ...... 11 Stream flows ...... 11 Water Balance ...... 11

LIST OF FIGURES Figure 21-1 Geographic extent Map ...... 3 Figure 21-2 Political boundary map ...... 5 Figure 21-3 Land Cover Map ...... 7 Figure 21-4 Drainage Map ...... 9 Figure 21-5 Sub-sub basin Map of Biñan Sub-basin ...... 10 Figure 21-6 Annual Stream flow, 1990 – 2004 ...... 11 Figure 21-7 Yearly Water Balances ...... 12

LIST OF TABLES Table 21-1 Geographic Extent ...... 4 Table 21-2 and Barangays Covered ...... 4 Table 21-3 Population Distribution by , 2007 ...... 6 Table 21-4 Land Cover Classification area and percentage ...... 6 Table 21-5 Some Relief Features and Other Geo-Morphological Parameters ...... 8 Table 21-6 Biñan Sub-sub basin properties ...... 11 Table 21-7 Yearly Water Balances based on model simulation (mm)...... 12

Technical writer For. Ma. Carolane P. Gonzales, 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 21. Biñan Sub-basin

Geographic location The Biñan Sub-basin (Figure 21-1) is situated in the western part of the de Bay Basin and southern part of Metro traversing the towns/cities of San Pedro and Biñan in the province of Laguna while the towns of Carmona, General Mariano Alvarez, Silang, City

The Biñan Sub-basin is bounded by Laguna Lake on the north and in the south. The Biñan sub-basin is bounded within the jurisdictional boundaries of six towns and a city which includes Biñan and San Pedro in Laguna, GMA, Carmona, Silang and Tagaytay City in . The geographic coordinates of the Biñan Sub-basin is listed below in Table 21-1.

Source: LLDA GIS Figure 21-1 Geographic extent Map Table 21-1 Geographic Extent CORNERS NORTHING (UTM) EASTING (UTM) Upper Left 1562641.25000 294844.93750 Upper Right 1562641.25000 280914.68750 Lower Right 1588909.12500 280914.68750 Lower Left 1588909.12500 294844.93750 Source: LLDA GIS

Political and Administrative Boundary The total land area of the sub-basin is approximately 8,406.732 hectares. Silang occupies more than one third of the total land area consisting of 29,308,944 square meters or about 34.86 %. Carmona and Biñan hold almost the same size of coverage with about 21,940,464 and 19,292,828, respectively. On the other hand, GMA, San Pedro and Tagaytay have small land area inside the sub basin with only 7,844,917 sq.m or 9.33%, 3,941,634 sq.m or 4.69% and 1,738,542 or 2.07%, respectively. See Table 21-2 and Figure 21-2 for municipal land area map within Biñan sub basin

Table 21-2 Municipalities and Barangays Covered Municipality/City No. Of Barangays Area (sq.m) Percentage Carmona 14 21,940,464 26.10 Binan 21 19,292,828 22.95 GMA 27 7,844,917 9.33 San Pedro 5 3,941,634 4.69 Silang 27 29,308,944 34.86 Tagaytay 3 1,738,542 2.07 TOTAL 97 84,067,328 100 Source: LLDA GIS

Source: LLDA GIS Figure 21-2 Political boundary map

Based on the 2007 Census of Population by the National Statistics Office, the total population within the sub-basin is estimated at 63,563. Pangil, having the largest area percentage making up the sub-basin, also shared the highest number of inhabitants with 36% or 23,187. It is followed by with 32% or 20,040 residents. Pakil has the most number of barangays (7) within the sub-basin. On the other hand, is the least populated at 341 (1%) though there are the four (4) of its barangays located within the jurisdiction of the sub-basin. Table 21-3 shows the detailed population data of each municipalities as well as the annual growth rate.

Table 21-3 Population Distribution by Municipality, 2007 Municipality/City Population Percentage BIÑAN 188,540 37.76 CARMONA 68,135 13.65 GMA 116,773 23.39 SAN PEDRO 79,740 15.97 SILANG 44,553 8.92 TAGAYTAY CITY 1,591 0.32 Total 499,332 100 Source: NSO, 2007

Land Cover

There are six (6) classes of land cover based on the result of the land cover validation done by LLDA, namely arable, brush, grass, marsh, plantation Majority of the sub-basin is covered by brush land with about 843.84ha or 37.14 % followed by grass land with an area of 690.60 ha or 30.39 %. The rest of the land cover is classified as plantation, arable, urban and marsh with an area of 315.46 ha or 13.88 %, 244.57 ha or 10.76%, 131.37 ha or 5.78%, and 46.50ha or 2.05%, respectively. Table 21-4 and Figure 21-3 show the estimated areas of the different land cover classes and the land cover map.

Table 21-4 Land Cover Classification area and percentage Land cover Area (sq.m.) Percentage Arable 244.57 10.76 Brush 843.84 37.14 Grass 690.60 30.39 Marsh 46.50 2.05 Plantation 315.46 13.88 Urban 131.37 5.78 Total 2272.331 100.00% Source: LLDA GIS

Source: LLDA GIS Figure 21-3 Land Cover Map

Sub-basin Characterization and Properties

Drainage Network Biñan sub-basin has an aggregate area of approximately 86 km2; the main channel length is about 30 km and drains north to northeast towards . The Biñan micro-watershed consists of three principal rivers namely, Biñan River, Soro-soro River and Carmona River. The Biñan River acts as the main river body while the Soro-soro and Carmona rivers serve as the tributary. The Soro-soro River has the longest channel length of about 29 km; the Biñan River has a stream length of 18 km, while Carmona River has stream length of 10 km. The headwaters of Biñan and Carmona River originate from the eastern slopes of the Cavite highlands while the Soro-soro tributary originates from Tagaytay. The drainage map of the Binan Sub-basin is shown in Figure 21-4 while the important watershed characteristics and geomorphological features are in Table 21-5.

Table 21-5 Some Relief Features and Other Geo-Morphological Parameters Parameters Values Area (ha) 8603.219 Perimeter (m) 65342.609 Total number of streams 51 Total length of streams (m) 96705.721 Stream Density (stream/ha) 0.00593 Drainage Density (m/ha) 11.2406 Constance of Channel Maintenance (ha/m) 0.0890 Length of Overland Flow (m) 5.620321 Source: LLDA GIS

Source: LLDA GIS Figure 21-4 Drainage Map

Sub-sub basin Properties

Source: LLDA GIS Figure 21-5 Sub-sub basin Map of Biñan Sub-basin Table 21-6 Biñan Sub-sub basin properties Sub-sub basin Name Area (Ha) Perimeter (m)

SSB-21A 2959.594 68210.756 SSB-21B 218.383 8445.651 SSB-21C 659.042 12191.146 SSB-21D 1596.081 28821.273 SSB-21E 761.261 24909.507 SSB-21F 495.158 12239.479 SSB-21G 569.176 17682.886 SSB-21H 388.904 10814.194 SSB-21I 955.621 24651.224 Source: LLDA GIS

Water Quantity

Stream flows The stream flow from 1990 to 2004 in Biñan sub basin is seen in figure 15-16 with the highest flow of 12.67819 cubic meters per second happened in 2000 and the lowest flow in 1994 with 1.6944 cubic meters per second as shown in Figure 21-6.

Source: LLDA PDMED Figure 21-6 Annual Stream flow, 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 Biñan sub basin, the long term water balances of the basin based on the hydrologic simulation is shown in the Table 21-7Error! Reference source not found.. The 15-year average would show that 45.3.1% of the total rainfall becomes surface run-off, and about 38.9% of rainfall is lost as actual evapotranspiration. The base flow component of the total run-off is quite minimal, with only about 144.7% of rainfall, while the remaining 1.1% is stored as soil moisture and contributes to groundwater aquifer Figure 21-7.

Table 21-7 Yearly Water Balances based on model simulation (mm). Actual Evapo- Direct Change in YEAR Rainfall Baseflow transpiration Runoff Storage 1990 2,337 699 1,373 391 (126) 1991 1,837 644 1,004 212 (23) 1992 2,015 656 1,050 212 98 1993 1,605 571 709 235 90 1994 1,138 692 372 213 (139) 1995 1,758 603 805 203 147 1996 1,777 728 846 214 (11) 1997 1,349 708 549 214 (121) 1998 2,028 620 968 191 248 1999 1,998 776 883 341 (2) 2000 4,684 796 3,374 490 24 2001 1,777 723 833 246 (25) 2002 2,098 630 1,200 219 49 2003 2,023 680 1,069 243 31 2004 1,647 675 778 172 21 Average 2,005 680 1,054 253 17 Source: LLDA PDMED

Source: LLDA PDMED Figure 21-7 Yearly Water Balances