Table of Contents

Volume 15. Pila Sub-basin ...... 3 Geographic location ...... 3 Political and Administrative Boundary ...... 4 Land Cover ...... 5 Watershed Characteristics and Drainage System ...... 6 Watershed Characterization and Properties ...... 6 Sub sub-basin properties ...... 7 Water Quantity ...... 10 Stream flows ...... 10 Water Balance ...... 10

LIST OF FIGURES Figure 15-1 Geographical map ...... 3 Figure 15-2 Political boundary map ...... 5 Figure 15-3 Land cover Map ...... 6 Figure 15-4 Drainage Map ...... 8 Figure 15-5 Sub-sub basin Map of Pila Sub-basin ...... 9 Figure 15-6 Annual Stream flow, 1990 - 2004 ...... 10 Figure 15-7 15-year Water balance based on model simulation ...... 11

LIST OF TABLES Table 15-1 Geographic extent ...... 4 Table 15-2 Municipalities and Barangays covered ...... 4 Table 15-3 Municipal population inside ...... 4 Table 15-4 Land Cover Classification area and percentage ...... 5 Table 15-5 Some Relief Features and Other Geo-Morphological Parameters ...... 7 Table 15-6 Pila Sub-sub basin properties ...... 7 Table 15-7 Yearly Water Balances of the Pila River Basin based on model simulation (mm)...... 10

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 15. Pila Sub-basin

Geographic location The Pila Micro-watershed (Figure 15-1) is situated in the southeastern part of the de Bay Basin covering four (6) , namely: Pila, Victoria, , Sta. Cruz, , .

Pila is located at 14° 233' N, 121° 364' E. Meanwhile, Victoria is situated at 14° 227’ N and 121° 328’ E while Sta. Cruz is located within 14º 17’ N and 121o 25’ E. On the other hand, Nagcarlan is located at coordinates 14º 08’ N and 121º 25’ E while Calauan lies at 14º 09’ N and 121º 19’ E. Lastly, Liliw is located at 14º 199’ N and 121º 429’ E at the South-Western part of Sta. Cruz. The coordinates of the Pila Sub-basin are presented in Table 15-1.

Source: LLDA GIS Figure 15-1 Geographical map

Table 15-1 Geographic extent CORNERS NORTHING (UTM) EASTING (UTM) Upper Left 1564234.62500 327737.50000 Upper Right 1564234.62500 316906.87500 Lower Right 1579749.12500 316906.87500 Lower Left 1579749.12500 327737.50000 Source: LLDA GIS

Political and Administrative Boundary The total land area of the sub-basin is 9,055.195 hectares. Pila sub-basin consists of 60 Barangays in six (6) municipalities. As exhibited in the Table 15-2, one-third of the sub-basin is situated in Pila covering 30 percent of the total land area. This is followed by Victoria, with 27 percent, Nagcarlan with 25 percent, Sta. Cruz with 16 percent Liliw with 0.15 and Calauan with only 0.08 hectares covered.

The total population in Pila Sub basin based on NSO survey in 2007 is 112,164. Most of the population come from the Municipality of Pila with about 39 % of the population in sub –basin. Victoria contributed about 29 % of its total population. The remaining municipality have minimal population contribution inside the sub basin. They are Sta Cruz, Nagcarlan, Liliw and Calaun with only25%, 6%, 0.23% and 0.07% of the total population inside sub basin, respectively as indicated in Table 15-3.

Table 15-2 Municipalities and Barangays covered No. Of Municipality/City Area (ha) Percentage Barangays Pila 17 2779.94 30.70 Victoria 9 2508.29 27.70 Nagcarlan 17 2290.96 25.30 Sta. Cruz 10 1457.89 16.10 Calauan 2 7.24 0.08 Liliw 4 13.58 0.15 TOTAL 60 9,055.19 Source: LLDA GIS

Table 15-3 Municipal population inside Municipality/City Population Percentage Pila 44056 39 Victoria 32594 29 Nagcarlan 6812 6 Sta. Cruz 28364 25 Calauan 81 0.07 Liliw 258 0.23 TOTAL 112,164 100 Source: LLDA GIS

Source: LLDA GIS Figure 15-2 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 arable land with about 3,076 ha followed by plantation with an area of 1,671 ha , urban at about 1,091 ha. The rest of the land cover is classified as forest, grassland, marsh and cloud with an area of 461 ha, 310 ha, 87 ha and 5 ha respectively. The unclassified areas comprise of about 67 ha of the sub basin. Table 15-4 and Figure 15-3 show the estimated areas of the different land cover classes and the land cover map.

Table 15-4 Land Cover Classification area and percentage Land cover Area (sq.m.) Percentage Arable 3,076 34.0 Brush 2,286 25.2 cloud 5 0.1 Forest 461 5.1 Grass 310 3.4 Land cover Area (sq.m.) Percentage Marsh 87 1.0 Plantation 1,671 18.5 Urban 1,091 12.0 Unclassified 67 0.07 Total 9,055 100.00% Source: LLDA GIS

Source: LLDA GIS Figure 15-3 Land cover Map

Watershed Characteristics and Drainage System

Watershed Characterization and Properties The peak flow and time it takes for the total flood flow to reach a given station are affected by the size of the watershed area. The larger the size of a given watershed, the slower the peak flow and it takes a longer time for runoff from the headwater to reach a given station. The boundary of a watershed is delineated by following the ridge surrounding the watershed, which is known as the natural or topographic divide (Figure 15-4). The Pila Micro-watershed is composed of two main river systems, which are the Banca-Banca river system and Pila river system. The Pila sub-basin has an area of 27.37 sq. km. and 21.93 km perimeter, has the highest elevation at rangers from 491 – 630 masl and the lowest at ~5.0 masl. Table 15-5 provides some relief feature and Geo-morphological parameters of the sub basins..

Table 15-5 Some Relief Features and Other Geo-Morphological Parameters Parameters Values Area (ha) 9055.195 Perimeter (m) 46009.663 Total number of streams 44 Total length of streams (m) 54371.320 Stream Density (stream/ha) 0.00486 Drainage Density (m/ha) 6.0044 Constance of Channel Maintenance (ha/m) 0.1665 Length of Overland Flow (m) 3.002216 Source: LLDA GIS

The length of the main stream indicates the steepness of the watershed. Steep and well-drained watersheds usually have numerous small tributaries. On the other hand, in the plains where the soils are deep and permeable, a watershed has relatively long tributaries, which are maintained as perennial streams. Map measure can be used to determine the length of the stream. The main stream’s length of Pila sub-basin (Pila River) is 6.95 km with a total of 44 streams including those which are intermittent. The total length of the streams is 54371.32 m while the stream frequency or density is 0.00486 stream/ha. Meanwhile the drainage density is 6.0044 m/ha. Its watershed shape factor is 0.71 with the general channel gradient at 0.29 percent.

Sub sub-basin properties

Table 15-6 Pila Sub-sub basin properties Sub basin Name Sub-sub basin Name Area (Ha) Perimeter (m)

Pila SSB-15A 3089.044 35856.926 Pila SSB-15A 0.000 0.344 Pila SSB-15B 177.752 6835.080 Pila SSB-15C 415.346 9944.284 Pila SSB-15D 1537.746 21979.708 Pila SSB-15E 2291.650 24218.874 Pila SSB-15F 1147.406 18001.823 Pila SSB-15G 396.252 12028.407 Source: LLDA GIS

Source: LLDA GIS

Figure 15-4 Drainage Map

Source: LLDA GIS Figure 15-5 Sub-sub basin Map of Pila Sub-basin

Water Quantity

Stream flows The stream flow from 1990 to 2004 in Pila watershed is seen in Figure 15-6 with the highest flow of 5.497163 cubic meters per second happened in 1999 and the lowest flow in 1997 with 2.02299 cubic meters per second.

Source: LLDA PDMED Figure 15-6 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 . 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 Pila sub basins, the long term water balances of the basin based on the hydrologic simulation is shown in the Table 15-7Error! 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.

Table 15-7 Yearly Water Balances of the Pila River Basin based on model simulation (mm). Actual Evapo- Direct Change in YEAR Rainfall Baseflow transpiration Runoff Storage 1990 2,399 762 1,252 431 (45) 1991 1,871 806 776 294 (5) 1992 1,892 757 865 252 17 1993 1,887 616 888 254 129 1994 1,508 803 555 260 (110) 1995 2,101 699 1,018 242 143 1996 2,078 816 1,045 253 (36) Actual Evapo- Direct Change in YEAR Rainfall Baseflow transpiration Runoff Storage 1997 1,330 742 446 221 (80) 1998 2,238 738 1,075 188 237 1999 2,586 779 1,375 420 12 2000 2,167 799 980 363 25 2001 1,719 818 614 303 (15) 2002 1,890 726 874 277 13 2003 1,843 767 770 297 8 2004 1,699 746 687 250 16 Average 1,947 758 881 287 21 Source: LLDA PDMED

Source: LLDA PDMED Figure 15-7 15-year Water balance based on model simulation