Physical Natural Characteristics
The City of Olongapo has a total land area of 18,500 hectares with about 2,352.34 hectares or 12.72% built up area. Development is constrained by the generally rolling/rugged mountainous terrain. It is geographically located at 14° and 50’ north latitude to 120° 17’ east longitude and lies 127 kilometers northwest of Manila, a two-hour drive on the average. It is located at the southernmost portion of Zambales Province, on the western coast of Central Luzon. The Municipality of Subic, northeast, bounds it on the north and northwest; by Dinalupihan, Bataan on the southeast by Morong, Bataan and Subic Bay on the southwest. The city is divided into seventeen (17) barangays.
Because of the massive mountain systems that characterized the area of the City, its topography is primarily rolling to steep and rugged along mountain ranges. Of its total area, about 80% is either rolling to steep and the rest are mainly deltaic flat areas which are usually found along the coast of Subic Bay. Based on available slope maps, areas which fall under the category of 0-8 percent or areas which are relatively flat cover about 20 percent of the land, and the rest have slopes ranging from 8 to more than 50 percent. Areas with steep slopes are located on the northern and eastern parts with an aggregate coverage of about 42 percent. In terms of elevation, most of the land is less than 500 meters above sea level.
There are two (2) major mountain ridges, the Kalaklan Ridge and the Salimpoyo Ridge both 1,000 feet above sea level. Kalaklan Ridge is located at the northwestern part of the city and its tip flows down to Subic Bay while Salimpoyo Ridge is located at the western side of the city. About 80% of the city’s land area has slopes of 18% and higher thus limiting land suitable for urban development.
The area is generally composed of volcanic rock which is deposited in various levels. Pyroclastic flows are prominent in the mountains and rock exposures are very common along cuts. On a very limited area like Olongapo City and at the Subic Bay Freeport (SBF), alluvial deposits are prominent especially along shorelines. The most common deposits consist of pyroclastic flows of quaternary origin.
In terms of geologic and foundation stability in the mountainous area, there are no limitations as to what type of structure may be built within the city. It should be considered, however, that due to the very stable and hard character of the rocks on the mountainous regions, earthmoving of this large mass to a flatter slope would indicate a very high cost due to the difficulty in ripping rocks. It is therefore suggested that as much as possible, proposed structures should be located in areas in which the most feasible foundation is appropriate. However, due regard for the volcanic surroundings and the frequent tectonic activities noted in the area must be made for such structures.
On the other hand, the US Navy during its occupancy of the area, conducted a foundation investigation of the areas within the then U.S. Facility now covered by the Subic Bay Freeport. In that study it was learned that there is a high probability that liquefaction will occur during an earthquake with a magnitude of 7 or greater on the Richter Scale with a maximum ground acceleration of 0.3 gravity. Thus, in areas where it is underlain with sandy substrate it is recommended that proper measures be observed in the establishment of foundation underneath the ground surface (World Bank, 1992).
Olongapo enjoys a generally pleasant maritime tropical climate. Average temperature is 80°F or 26°C. Humidity ranges from 75 to 80 degrees. Just like in other parts of the country, the City of Olongapo has two (2) distinct seasons: the dry and the wet seasons. The dry season is from March to June while the rainy season is from July to October. The intervening months of November to February are either too dry or too wet depending on the national situation. The most number of typhoons occur during the month of August.
For the City of Olongapo, the main source of water is the Santa Rita river basin. This particular watershed has a total area of about 92.4 sq. kilometers, with Santa Rita River as its main river which drains into Subic Bay. From the surface water map, Santa Rita River has seven (7) major tributaries. These include Mabayuan, Pamo, Naguraw, Tawirang-Balite, Jadjad, Iram and Licab. Since much of the City lies within an alluvial floodplain, it is also susceptible to perennial flooding, with 10 barangays experiencing chronic floods.
Aside from the Santa Rita River and Mabayuan Creek, Olongapo City also relies on groundwater source for its water supply system. A deepwell is found in San Isidro which supplies the water requirements of Barangay Barretto. In 1999, the beach resort – rich village of Barretto began drawing water from the Subic Water District to supplement its growing needs. Olongapo City also draws from a spring situated in the upland areas of Barangay Cabalan.
Within the Subic Bay Freeport Zone (SBFZ), sources of water are mainly from the Binictican watershed. Others come primarily from Boton and Malawaan rivers which are also located inside the former military reservation. The watershed of the SBFZ is presently covered with forest with some areas allotted for urban use. In the World Bank Report, it was found out that the surface water supply of the SBFZ is not enough to meet the future water demands. It is therefore imperative that with the future growth and development of the former naval facility, an alternative source of water should be determined in the near future. Current projects funded by the World Bank include developing new wells and drawing raw water from whatever sources will the result of the study be, to anticipate this future need.
The most predominant type of land use in the area is grassland or shrublands which cover about 65 percent of the total land area of the City and SBFZ. They are usually found at elevations less than 500 meters above sea level. Practically all of the area has significant lands devoted to grasslands and shrublands. Grasses found in the area come in various types but the most dominant is cogon (Imperata cylindrical). Aside from cogon, there are also talahib (Saccharum Spontaneum), and buho (Schizostachum Lumampas).
Forest lands, on the other hand, cover only 30 percent of the project area. These lands are found inside the former Subic Naval Reservation, particularly in the Boton and Binictican watersheds and parts of the Bataan National Park in Morong. These are also forest lands located in the uplands of Olongapo City.
Trees found in the area are classified into two (2) namely; dipterocarp and non-dipterocarp. Under the dipterocarp group , tree species found include apitong (dipterocarpos grandiflorus) and white lauan (Shorea Contorta). Examples of non-dipterocarp is kupang (Parkia roxburgii). Aside from trees, non-timber species (Calamus species), ferns, vines, and other low growing plants. The rest are either devoted to built areas or agricultural land.
The present urban land use is typical where the majority of the commercial and institutional establishments are lined up along the major thoroughfares of the city. The inner blocks nearest to the main streets basically have a mixed land use, which is either commercial or residential. The interior sections are primarily residential apartments and houses.