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Home , Cabuyao, Laguna (province), Tagaytay

Table of Contents

Volume 18. San Cristobal Sub-basin ...... 3 Geographic location ...... 3 Political and Administrative Boundary ...... 4 Land Cover ...... 5 Sub-basin Characterization and Properties...... 7 Drainage Network ...... 7 Sub-sub basin Properties ...... 9 Water Quantity ...... 10 Stream flows ...... 10 Water Balance ...... 11

LIST OF FIGURES Figure 18-1 Geographical Map ...... 3 Figure 18-2 Political boundary map ...... 5 Figure 18-3 Land Cover Map ...... 6 Figure 18-4 Drainage Network ...... 8 Figure 18-5 Sub-sub basin Map of San Cristobal Sub-basin ...... 9 Figure 18-6 Annual Stream flow, 1990 – 2004 ...... 10 Figure 18-7 Water Balances based on model simulation, 1990-2004 ...... 11

LIST OF TABLES Table 18-1 Geographic Extent of San Cristobal Sub-basin ...... 4 Table 18-2 Municipal land area ...... 4 Table 18-3 Population ...... 4 Table 18-4 Land Cover Classification area and percentage ...... 6 Table 18-5 Some Relief Features and Other Geo-Morphological Parameters ...... 7 Table 18-6 San Cristobal Sub-sub basin properties ...... 10 Table 18-7 Yearly Water Balances based on model simulation (mm)...... 11

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 18. San Cristobal Sub-basin

Geographic location The San Cristobal (Figure 18-1) Sub-basin is situated in the western part of the de Bay Basin covering six towns/cities, namely: Calamba City, , Santa Rosa City, Silang, City, Talisay and Tanauan City.

Calamba City, Cabuyao and Santa Rosa City are all in the Province of Laguna. Calamba City is bounded on the east by . Silang is situated on the eastern part of Province. Cabuyao is located at the northern part of the province and is 45 km away from . Tagaytay City is located in the Province of Cavite and about 56 km south of Manila. Santa Rosa City, Laguna is located 40 km south of Manila. It is bounded on the northwest by Biñan, on the south and southwest by Cabuyao and on the west by the province of Cavite. Bordering the northeast is Laguna de Bay. Another LGU within the San Cristobal Micro- watershed is Talisay and Tanauan City, also in the province of .

Source: LLDA GIS Figure 18-1 Geographical Map

Table 18-1 Geographic Extent of San Cristobal Sub-basin CORNERS NORTHING (UTM) EASTING (UTM) Upper Left 1562334.98913 304314.87500 Upper Right 1562334.98913 281913.90739 Lower Right 1576597.91657 281913.90739 Lower Left 1576597.91657 304314.87500 Source: LLDA GIS

Political and Administrative Boundary The total land area of the sub-basin is 14,065.926 hectares. Calamba City occupies 50.76% of the total land area which can be found in the middle part of the sub-basin to the lakeshore of the Laguna de Bay. Silang, Cabuyao, Tagaytay City, Santa Rosa City, Tanauan City and Talisay share 21.31%, 11.85%, 10.69%, 4.76%, 0.60% and 0.03%, respectively. See Table 18-2 and Figure 18-2 for municipal land area/map within San Cristobal Sub-basin.

Table 18-2 Municipal land area No. Of /City Area (sq.m) Percentage Barangays Cabuyao 8 16,622,836 11.85 Calamba 26 71,232,654 50.76 Sta. Rosa 2 6,681,050 4.76 Tanauan 2 844,690 0.60 Silang 8 29,903,709 21.31 Tagaytay 11 15,003,024 10.69 Talisay 2 48,108 0.03 TOTAL 59 140,336,070 100 Source: NSO, 2007 As of year 2007, the total population making up the San Cristaobal sub-basin is estimated at 292,141. Among the three , Calamba has the highest population of 191,216 accounting for 65% of the total followed by Cabuyao which has the population of 67,047 representing 23% of the total (Table 18-3)

Table 18-3 Population Municipality/City Population Percentage Cabuyao 67047 23 Calamba 191216 65 Sta. Rosa 1237 0.42 Tanauan 407 0.14 Silang 21532 7 Tagaytay 10654 4 Talisay 48 0.02 TOTAL 292141 100 Source: LLDA GIS

Source: LLDA GIS Figure 18-2 Political boundary map

Land Cover

There are nine (9) classes of land cover based on the result of the land cover validation done by LLDA, namely arable, brush, cloud, forest, grass, marsh, plantation, urban, and unclassified. Majority of the watershed is covered by grass land with about 5036.1 ha or 35.8 % followed by brush land with an area of 4023.2 ha or 28.6 %, arable with an area of 1936.4 ha or 13.8 % , urban with an area of 1827.6 or 13 %. The rest of the land cover is classified as plantation, marsh, cloud forest, and with an area of 1174 ha or 8 %, 37 ha or 0.3%, 8 ha or 0.1%, and 4.2 ha or 0.02%, respectively. The unclassified areas comprise of about `1.5 ha or 0.01% of the sub basin. Table 18-4 and Figure 18-3 show the estimated areas of the different land cover classes and the land cover map.

Table 18-4 Land Cover Classification area and percentage Land cover Area (sq.m.) Percentage Arable 1936.4 13.8 Brush 4023.2 28.6 cloud 8.0 0.1 Forest 4.2 0.03 Grass 5036.1 35.8 Marsh 37.0 0.3 Plantation 1174.0 8.4 Unclassified 1.5 0.01 Urban 1827.6 13.0 Total 14048 100.00% Source: LLDA GIS

Source: LLDA PDMED Figure 18-3 Land Cover Map

Sub-basin Characterization and Properties

Drainage Network The major surface water resource in the San Cristobal River and its tributaries. The San Cristobal River System, one of the major tributaries draining into the Laguna de Bay, is among the most polluted river affecting the lake's productivity and survival. Its basin represents a typical agro-industrial condition/setting which if properly and scientifically managed could serve as a model for development to other basins with similar or potential characteristics. It contributes about 5 percent of the total freshwater discharge into the Lake.

The drainage map of the San Cristobal Sub-basin is shown in Figure 18-4 while the important watershed characteristics and geomorphological features are in Table 18-5.

Table 18-5 Some Relief Features and Other Geo-Morphological Parameters Parameters Values Area (ha) 14065.926 Perimeter (m) 61936.562 Total number of streams 103 Total length of streams (m) 264480.222 Stream Density (stream/ha) 0.00732 Drainage Density (m/ha) 18.8029 Constance of Channel Maintenance (ha/m) 0.0532 Length of Overland Flow (m) 9.401450 Source: LLDA GIS

Source: LLDA GIS Figure 18-4 Drainage Network

Sub-sub basin Properties

Source: LLDA GIS Figure 18-5 Sub-sub basin Map of San Cristobal Sub-basin

Table 18-6 San Cristobal Sub-sub basin properties Sub-sub basin Name Area (Ha) Perimeter (m) SSB-19A 1017.149 33292.437 SSB-19B 1236.248 24312.851 SSB-19C 276.796 7946.889 SSB-19D 3160.055 57768.765 SSB-19E 292.739 12616.751 SSB-19F 560.266 18727.885 SSB-19G 444.045 18176.377 SSB-19H 1032.396 23217.704 SSB-19I 997.950 26137.283 SSB-19J 368.966 13095.490 SSB-19K 355.435 12040.593 SSB-19L 1256.519 23314.229 SSB-19M 1100.018 22051.880 SSB-19N 558.656 17940.691 SSB-19O 329.502 11627.080 SSB-19P 808.549 20232.287 SSB-19Q 270.284 7376.881

Water Quantity

Stream flows The stream flow from 1990 to 2004 in San Cristobal sub-basin is seen in Figure 18-6 with the highest flow of 10.85393 cubic meters per second happened in 2000 and the lowest flow in 2004 with 3.808363 cubic meters per second as shown in Figure 18-6.

Figure 18-6 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 San Cristobal Sub-Basin, the long term water balances of the basin based on the hydrologic simulation is shown in the Table 19-10Error! Reference source not found.. The 15-year average would show that 0.9% of the total rainfall becomes surface run-off, and about 34.9% of rainfall is lost as actual evapotranspiration. The base flow component of the total run-off is quite minimal, with only about 14% of rainfall. Table 18-7 Yearly Water Balances based on model simulation (mm). Actual Evapo- Direct Change in YEAR Rainfall Baseflow transpiration Runoff Storage 1990 2,386 714 1,380 398 (107) 1991 1,940 715 974 241 10 1992 1,923 677 937 234 75 1993 2,008 597 1,024 292 95 1994 1,581 731 693 281 (124) 1995 2,130 638 1,087 261 144 1996 1,908 736 972 232 (32) 1997 1,727 709 859 250 (91) 1998 2,459 622 1,334 227 276 1999 2,252 785 1,088 395 (15) 2000 3,238 809 1,917 481 32 2001 1,721 786 690 286 (42) 2002 1,699 649 817 220 12 2003 1,555 675 683 198 (2) 2004 1,602 683 637 231 50 Average 2,009 702 1,006 282 19

Figure 18-7 Water Balances based on model simulation, 1990-2004