The existing drainage facility of the City consists of concrete- lined canals, open ditches, sidewalk gutters and reinforced pipes laid- out mostly in the City proper. Drainage lines are mainly covered in the City proper, particularly in areas where there is a large volume of traffic. These run alongside City roads and drain into Matanglad River which then flows northward. However, momentary flooding is experienced during heavy rains due to some clogging along the lines. Declogging and desilting have to be done in order to prevent similar events from happening.
Ligao has no centralized sewerage system to treat wastewater coming from various sources. This is one of the sanitation related problems, which renders parts of the City prone to health risks. Domestic and commercial wastes are usually disposed of in individual septic tanks which discharge into waterways, drainage canals or made to percolate underground.
In the recent past, Ligao experienced one of the most devastating flood events that affected City residents in terms of lives lost and damage to infrastructure, properties and crops. Due to this life threatening situations, it is important that the people are protected and their livelihood secured in order to assure development and progress within the City.
Water contamination is quite evident with the discharges in the urban creeks and rivers. Contaminated water flow downstream and result in contamination of the downstream environment, posing threat to the ecosystem and health and welfare of the residents. It is important that measures be taken to mitigate this situation and protect the environment and health of the residents.
Drainage and Sewerage
One of the urban problems besetting cities in the Philippines is flooding, and this has become common in Ligao as evidenced by the previous disastrous flood and mudflow the occurred in year 2006. This is due to the fact that intensive commercial and residential development in Ligao has overtaken the investment in infrastructure, particularly in terms of drainage facilities and flood control infrastructure. Since the existing urban core is downstream of the Mayon Unit which is at higher elevation, the risk of flooding is a perennial occurrence, affecting residences and businesses, prompting the city as well as the national government to implement major flood-mitigation infrastructure for the city. Aside from the major national government infrastructure, there are a number of important issues that need to be addressed such as :
- Under-capacity drainage lines – As urbanization heightens in Ligao heightened its urbanization, the urban land use also changed dramatically increasing the paved areas and correspondingly increasing the runoff volume of surface water runoff. Because of this uUrban drainage lines which were designed for lower runoff volume are suddenly became under-capacity and which resulted to flooding in some of the city’s streets. In addition, silt deposits over the years have also lessened the area of flow inside drainage lines, thus these aremaking these easily filled up which also and resulted in street flooding. Several places were identified as flood prone and the immediate measure is to rehabilitate existing drainage lines in these places which can be funded by the city.
- Accumulated garbage in waterways – Inadvertent dumping of solid waste in waterways resulted to decreased capacity, which results in overtopping of embankments. As uncollected or scattered garbage are left on the streets and go with the flow into street drainage lines and canals, clogging of these lines occur thus also resulting also in the flooding of urban streets.
- Combined drainage and sewer lines – Since the city lacks sewer lines, the wastewater from residential and commercial areas alsoare mixed with the runoff water. ; thus tThe combined volume results into higher water volume to be conveyed by existing drainage lines. This situation also contributes to flooding in urban streets.
- Absence of clear and effective program for watershed management – With the denudation of the watershed areas at the headwaters of the rivers, such as the Matanglad River, which drainsing into Ligao, the massive flashflood waters flow down causing inundation in the lowlands resulting in destruction to lives, properties and public infrastructure. Hence, it is necessary to focus attention on the situations at the watershed areas to lessen or decelerate the flow of runoff into the lower regions.
- General Issues on climate change and variations in weather pattern – With the eventual shifting in weather patterns and climatic conditions bringing degrees of variation to rainfall, it is expected that runoff will be increasing. This will result in more frequent and probably increased possibility of flooding.
Due to the inherent surrounding topography of the urban core of Ligao City, flooding is not an uncommon occurrence. In recent years, the occurrences of flooding have become more and more threatening due to heavy rains caused by erratic climatic conditions brought about by the global change in climate. This is further aggravated by the denudation of forests in the Mayon Unit areas.
Severe flooding in the city, with flood waters reaching around one to two meters on the streets, has been experienced along the National Highway at the junction with Naiera Street. Flood waters gushed forth from Matanglad River which originates at the catchment areas at the side ridges of Mt. Mayon as well as from the watersheds at its foothills. This was probably aggravated by the silted waterways of the Matanglad River as it runs into a mildly serpentine reach through the Urban Core.
Debris deposited at the river bed impedes the flow of water causing deceleration of floodwater as it rushes down. This deceleration causes a backwater effect which, in turn, causes swelling in some areas. Another possible cause may be the accumulated garbage debris which ends up into the river, either from upstream or from various locations within the city. Garbage o n the river bed would tend to lessen the conveyance capacity of the river resulting in excess water overtopping the banks and consequently flooding the city streets.
The streets in the Urban Core area have drainage lines with their outfalls discharging into Mantanglad River and to other waterways located at the western part of the city. Over the years, it is expected that the efficiencies of these drainage lines would somehow decrease due to the accumulation of silt and other materials. It is important that these drainage lines be inspected to find out how to improve their draining efficiencies to reduce or prevent the accumulation of flood waters in the city streets.
The flooding and drainage situations in the city’s urban core are depicted below.
Flooding and Drainage Situation for Ligao City Urban Core
Coupled with the problems of flooding, the issue of waste water and sewerage has also been a cause of concern. Currently, untreated wastewater is being discharged directly into the waterways causing contamination of the water bodies. This contaminated water threatens not only the physical environment and the ecosystem, but also the health and welfare of the local population. In the Urban Core, waste water originating from residential and commercial areas discharge directly into city canals which outfall into Matanglad River and other waterways at the western areas. This cause the contamination of the existing surface water causing pollution to areas downstream.
Water contamination problems in the coastal areas were brought to the attention of city officials . Although not as severe, the discharges of liquid, and sometimes solid waste, cause the contamination of the coastal areas which have unfavorable consequences to its marine and fishery resources as well as tourism potentials .
Some mitigation measures need to be done to avert the immediate disaster of flooding and the growing threat of water contamination. The following are the measures which need to be addressed with reference to the Drainage and Sewerage Scheme for Ligao City’s Urban Core.
- Control of flood waters – As described, flood waters originate from the Mayon Unit areas winding into the water ways which run through and alongside the Urban Core particularly the Matanglad River and the Nasisi River. Of the two rivers, Matanglad River’s tributaries, particularly the eastern tributary, have been found to be the major causes of flashflood in the Urban Core. By controlling the flow into the eastern tributary either by a flood gate upstream or by a diversion channel, it may be possible to lessen the floodwaters, which cause the inundation of city streets. The flood infrastructure will consist of flood control gates and diversion channels, the purpose of which is to divert the flow to other tributaries or to other waterways which can safely convey the flow with less detrimental effects downstream. These shall be located along the peripheries of urban areas and selected Barangay Centers, especially along waterways. The scheme is shown below.
- Desilting and Clearing of the Lower Reaches of Matanglad River. The Matanglad River, especially its reaches inside the city’s Urban Core, is already silted over the years due to deposition of materials swept from its upstream sources. Also, garbage debris inadvertently thrown into the waterways has contributed to the slowing down of water flow, lowering its conveyance capacity and consequently flooding some parts of the city’s uUrban cCore. Maintenance of the silted reaches of Matanglad River becomes necessary by clearing and removing deposited materials from its bed. This activity should be done practically from the point where the river enters the urban area until its confluence near the railroad tracks. Soil and other deposited materials that have been removed shall be disposed in areas where fill materials are needed, while solid waste should be disposed in the city’s disposal facility.
- Drainage Improvement inside City Streets. Runoff within the city is expected to increase over the years due to lesser chances of ground infiltration and retarded overland flow. This situation is caused by paving of certain areas due to increasing settlements and consequently the expansion of Ligao City’s Urban Core. Because of these situations, some of the city’s drainage lines are will be rendered under-capacity resulting in somecases of momentary flooding. In addition, a number of the drainage lines may already be silted and the reduced flow capacity also contributes to momentary flooding. It is important that a thorough investigation of the drainage lines be done, and to undertake rehabilitatione of old lines as well as toand construct new drainage lines along for some of the streets within the uUrban cCore.
- Drainage Master Plan for the City’s Urban Core. With the changing landscape in the surroundings of Ligao City as well as the increased development of the Urban Core, it is important that the city’s drainage infrastructure be made responsive. Henceforth, more proactive planning should be done in conformance to the projected land use. The Drainage Master Plan shall incorporate improvements and construction of infrastructure within the urban core and along peripheral waterways in order to secure the area from unprecedented flooding which have become more and more frequent.
- Establishment of Wastewater Treatment System. With increasing urbanization and development, one of the environmental threats that the city is facing is pollution and contamination of surrounding water bodies. As stipulated in R.A. No. 9275 or the Clean Water Act, water districts are mandated to provide sewerage services to their respective areas. Also, as stated in this Act, LGUs shall identify suitable sites for the location of future waste water treatment facilities. With respect to suitability , one major consideration would be the availability of the sites, preferably the lowest point in the catchment area and proximity to points of discharge . The areas suitable for this purpose are those near the Matanglad and Nasisi Rivers at the western edge of the Urban Core as indicated below.
- Protection of Water Quality in the Coastal Areas. The increasing population and consequently, increase in the number of settlements in the coastal areas have also brought some concerns over the deterioration of water quality of the coastal regionstherein. This , which is detrimental not only to the marine and fishery resources but also to the tourism values of the beaches. It is important that water quality in the coastal waters be protected and its pristine quality be maintained through constant monitoring of water quality, construction of as well as implementing infrastructure and implementation of management measures to prevent pollution. The monitoring of wWater quality monitoring can be done by the City’s environmental division in cooperation with regional offices of the DENR and the DA through the BFAR. Infrastructure measures will may be in terms of drainage, septage/sewerage and solid waste facilities which need to be established in the barangays along the coast. Management measures shall may be in terms of education and information campaigns and, advocacy and awareness-building among constituents. These shall empower them to manage solid and liquid waste being discharged in order to minimize or prevent altogether coastal contamination and pollution.