MMSU Science and Technology Journal ISSN: 2012 0060 Vol. 4 No. 1/January-June 2014

THE HYDROLOGICAL CAPACITY OF THE QUIAOIT RIVER WATERSHED (QRW)

Virgilio Julius P Manzano Jr.* and Nathaniel R. Alibuyog

Abstract

Water balance and hydrological processes under changing climate, land-use, and land cover at various scales (temporal and spatial) were investigated upon at the Quiaoit River Watershed (QRW) in , . Dependable groundwater and surface water supply vis-a-vis water demand for agricultural, domestic, environmental, and commercial purposes were assessed and examined. Data sets were gathered using- field based monitoring at the point, reach, and catchment scales.

Results indicate that water demand for all uses within the QRW is 138,865m3/day, which is around 42% of the estimated Total Resource Capacity of 336,100.8m3/day. This implies that water supply is presently adequate to meet existing agricultural (172,065.1m3/day) and domestic (10,370.4m3/day) needs. Nonetheless, supply is coming under pressure from changing land-use and urban development. In addition, land cover has changed drastically in the QRW, which imposes a negative impact on its water resources. The built-up area has almost doubled (391.24 to 743.69ha) in seven years. As such, the area of inland water decreased from 257.95ha to 33.50ha due to the increasing extraction of water for agricultural use.

Keywords: changing climate, land-use, land cover, agricultural demand, dependable groundwater and surface water

*Corresponding Author: Current Address: MMSU-College of Engineering, City of , Ilocos Norte e-mail: [email protected]

12 VJP Manzano Jr and NR Alibuyog Hydrological Capacity of QRW

Introduction The Quiaoit River Watershed (QRW) is a sample case, because it is the major Inherent in the growth of a community source of domestic water supply and are the disturbing issues of its water irrigation for thousands of Ilocanos in the City resources. The peculiarity is derived from a of Batac and the towns of and combination of factors; among them is the . While water resources in the QRW interaction of sustained increase of maybe considerable, they are not infinite. To population and activities with water and land know the reliable and dependable water, it is over limited space. The increase in indispensable to determine the water population per unit area necessitates a balance of the QRW vis-a-vis the number of proportionate increase in water demands its users. from agricultural, environmental, industrial, and domestic purposes. With limited water Due to the constraints of available resources among competing users, the trend information, the study assessed the extent of of development has been reoriented to water supply availability in the QWR, Batac protect the economic, social, and City, Ilocos Norte, as well as its capability environmental needs for future generations and sustainability in coping with future water and to provide secure and equitable access demands. Likewise, it looked into empirical to water for all users. data as bases for developing a transparent process that will serve as anchor in Population pressure and continuous formulating effective and efficient water denudation of the watersheds exacerbated resources management policies. Specifically, the declining water resources availability of the research quantified water supply and a locality. In fact, water resources are the water demand/requirements in the most important condition for agricultural agricultural, domestic, environmental, and development heading to economic commercial sectors of the QRW. Through the development and progress of a society. This findings, policy makers would have a basis in necessitates an efficient planning and evaluating responses to potential shortfalls of management of the watershed in a locality water supply in the future. to maintain a reliable and adequate water supply. There is an increasing awareness Methodology that water resources exist in limited quantities, and available supply varies Locale and Description of the Study Area considerably in a year. Hence, the The QRW has a total land area of management process of water resources 2 must prevent and resolve conflicts among 190.18km covering the City of Batac and the different users (Lilburne et al, 1998; Salman municipalities of Paoay and Currimao, Ilocos et al, 2001). Norte (Figure 1). About 70% of the total watershed area is located within the city Demand pressure on the existing itself. It is located in the northwest corner of vital water resources from agriculture, the island of , about 11km (6.8mi) from domestic, environment, and industry is the eastern shores of the . It anticipated to rise progressively and soar up summits as high as 520m above sea level. dramatically in the next decade. With the The watershed falls within latitude 17° 07’ increased water requirements for social and north and longitude 120° 32’ to 120° 28’ east. economic activities, possible water shortage The area is about 18km to City, the which has already been experienced by province capital; 225km to the regional other localities elsewhere, may pose serious center (San Fernando, ), and about threats. 472km to Metro .

13 VJP Manzano Jr and NR Alibuyog Hydrological Capacity of QRW

and planted to rice during the wet season. During the dry season, corn, tobacco, and vegetables are planted. On the upland and hilly areas, agricultural activities are also common along the river, tapping its water for irrigation especially during the dry season. Most of the commercial activities are concentrated in the central and western parts of the watershed.

Demographic Characteristics

Demographic attributes of the study area such as population size, growth rate, number of households, as well as the age and sex structure, educational attainment, income, sources of income, etc. of the resident-respondents were gathered. The descriptive method of research was used. Structured questionnaires were primarily used to gather needed demographic data. Meanwhile, supplemental information was Fig.1. Quiaoit river watershed boundary gathered from secondary data and through showing the administrative boundaries interviews. covered and its relative location in the province of Ilocos Norte Water Resources Inventory and Estimation of Water Supply The climate is Type I, with two Water supply is the amount of water pronounced seasons - dry (from Nov to Apr) available for use from the discharge of and wet (during the rest of the year). The surface water and groundwater sources. average annual rainfall is 2550mm (100.39 Series of water resource assessments in the inches). Great seasonal temperature ranges study area were conducted to estimate water befall the area. The highest temperature is supply availability. recorded in Apr and May with an average of o as high as 34.1 C. The area is exposed to A. Surface Water southeast monsoon and cyclonic storms. Frequently, 30% of the weather Streamflow data sets were gathered disturbances, which hit the Philippines every from the network of automatic stream year, dash across the project area. However, gauging stations that were installed for this it is shielded from the northeast and trade study. The class interval method was winds by the mountain ranges of the followed in constructing the flow duration Cordilleras. The average relative humidity of curves for monthly and seasonal streamflow the area is 78.4%. Climatological data were data. The 80%-time availability of flow was obtained from the MMSU Agromet Station taken as the dependable proportion for and from PAGASA-Laoag Station. agricultural and domestic purposes.

At present, the pattern of cultivation is Further, a survey of all currently closely related to the slope or landform. The available reservoirs and water impounding level lowland areas are intensively cultivated structures in the area was done. Their

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Fig. 2. Climate of the Quiaoit River Watershed capacity and other technical characteristics Recharge Estimation were recorded. The watertable fluctuation method B. Groundwater Supply (Healy and Cook, 2002; Risser et al, 2005) was used to estimate the recharge. This Groundwater characteristics such as method was based on the premise that the Transmissivity (T), Hydraulic Coefficient (K), rise in groundwater levels in unconfined and Storage Coefficient (Sc), which served aquifers was due to the recharging water at as basis for the ability of groundwater to the water table. Recharge was calculated meet the required current and projected using the formula: water demand were determined using pumping tests. dh h  h R  S  S 2 1 y dt y t Likewise, the safe water yield and approximate volume of water withdrawal from groundwater resource were estimated Where: R = recharge rate, from actual aquifer testing. Existing shallow Sy = specific yield, and deep wells in the study area were dh = change in water level, and randomly selected as the test wells. dt = change in time. Meanwhile, additional groundwater information was obtained from the Shallow Tubewell (STW) Irrigation Project – Groundwater fluctuations were Department of Agriculture-University of the monitored twice a month in each of the Philippines Los Baños. established observation wells.

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Estimation of Current and Future Demand share of average precipitation that is likely to contribute to crop needs. The net This activity involved estimating the requirement was corrected according to soil current and projected water demand for permeability (some water is lost by domestic and agricultural purposes in the percolation), as well as via an efficiency study area. coefficient that considers the plot irrigation, which is conducive to some water loss at the Domestic water demand drainage end (http://www.fao.org/docrep/ s2022e/s2022e07.htm). Population data (10-15 years record), per capita consumption, levels of economic Evapotranspiration (ET). Actual water productivity, and the like were gathered from consumption (evapotranspiration) of crops the Socio-Economic Profile filed at the City planted in the QRW was estimated using the Engineering and Planning Office of Batac Fao-Penman Monteith equation. It was City. Additional data sets were gathered adapted from the FAO Irrigation and through interviews and questionnaires. Drainage Paper No. 56.

On the other hand, domestic water Influencing factors that determined demand was determined through this the amount of evapotranspiration include the formula: climatic factors (air temperature, humidity, radiation, cloud cover, and wind) and the Domestic Water Demand (lpd) = per capita nature of the plants together with their growth consumption X population stages. Influence of the amount of moisture in the soil at the time (soil moisture tension) Projection of future population was also considered. On the other hand, the estimates was computed using a) Short major factors that estimated the irrigation Term Estimate (Geometric Growth Method) water requirements are as follows: 1) and b) Long Term Forecasting (Mathematical evapotranspiration; 2) crop growth stages; 3) Logistic Curve Method). water available within the root zone of the soil; and 4) soil drainage and water lost Different scenarios of water demand through seepage and deep percolation. were formulated to analyze the corresponding effects of each scenario on Inventory of livestock and poultry water supply availability in the future. farms. Actual survey and inventory of livestock and poultry farms were done. The Agricultural Water Demand (including point location of these establishments were Livestock and Poultry) noted using GPS.

Crop water requirements. Monthly water Mapping requirements of the crops in the area were determined using a simple formula. The crop The GIS programs, such as ArcInfo area is multiplied by the reference and ArcView, were used to generate needed evapotranspiration (ET), with an additional maps to show the location, boundaries, and multiplicative crop coefficient (Kc), indicating water users of the study area. plant requirements relative to ET. Rainfall was then accounted for by estimating the

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Results and Discussion 259,292.40m3/day. On the other hand, the daily available surface water supply amounts Water Supply to 59,303.63m3/day and 17,504.81m3/day for the wet and dry season, respectively. Given The water sources are surface and these flow rates, it is not surprising that it groundwater. Surface water in the study area easily runs dry during the dry season. is extracted for irrigation and other purposes using pumping systems. The latter is readily The total amount was estimated to be being tapped through shallow tubewells and 336,100.84m3/day. Logically, if the quantity is the major source of irrigation and other of water taken from QRW exceeds the purposes during low flows of surface water, usable supply, the river will die off and will normally during the dry season. All in all, the run dry eventually. QRW has around 2000 shallow tubewells, two Small Water Impounding Projects Estimated Groundwater Recharge (SWIPs), and several watercourse extraction and Safe Yield points. Groundwater recharge in the QRW is The usable supply of ground and due almost exclusively to aerial recharge surface water is the proportion of water from precipitation and its magnitude is suitable for a particular purpose, which can controlled by groundwater evapo- be efficiently. This should be available over a transpiration. As shown in Table 2, long period and its withdrawal should be calculated groundwater recharge was ecologically acceptable (Schiller, 1992; 529,381.95m3/day corresponding to 51.81% Evans and Evans, 2011). The daily available of the annual rainfall. water supply is shown in Table 1. Usable water progressively dropped as the dry On the other hand, nothing can be season advances following the lowering of said about the long-time record of the annual the magnitude of rainfall, which is already change in water table level and annual draft very minimal in the second month (Nov) of in the study area for safe yield computation. the dry season. This decrease in usable This reflects one limitation of the study. water supply is compounded by higher Nonetheless, based on the generally-valid evapotranspiration. Groundwater and surface criteria that water withdrawal should not water supplies begin to be replenished at the exceed the natural recharge amounts, the onset of wet season (normally in late May) safe yield was taken as 60% of the long-term and reach a peak corresponding to the natural groundwater recharge (volume highest magnitude of rainfall. basis). Additionally, the safe yield percentage was based on the groundwater resources The volume of groundwater that can studies by Burgh (1975) and Pastor (1998), be safely withdrawn across seasons is who suggested that at least 67% of the

Table 1. Usable supply of surface and groundwater ESTIMATED AMOUNT (m3/day) SOURCE TOTAL Wet Season Dry Season Surface water 59,303.63 17,504.81 76,808.44 Groundwater (Safe Yield) 143,632.20 115,660 259,292.40 TOTAL 202,935.83 133,165.01 336,100.84

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potential recharge amount is the drawdown and subsequent water extraction recommended limit to be extracted to avoid from the lower aquifer, which may deteriorate undesirable effects like groundwater ‘mining’. the water quality. Furthermore, the assumption of safe yield was implied by its definition: Safe yield is the Water Demand: Domestic and Agricultural amount of naturally-occurring groundwater that can be withdrawn from an aquifer on a The map of major water users in the sustained basis, economically and legally, QRW is shown in Figure 3. The biggest without impairing the native groundwater chunk of water demand was tied up with quality or creating undesirable effect such as agriculture. On the other hand, a environmental damage (Fetter, 1994). With considerable portion was attributed to this, computed safe yield was 317,629.17 domestic demand, while commercial m3/day. establishments imposed a negligible demand. If the water discharge is higher than its recharge, it would lead to water table

Table 2. Estimated recharge rate and volume, and safe yield in the QRW

RECHARGE (Based on Water Balance) RECHARGE SAFE YIELD LOCATION AREA (ha) Rate (%) Volume (m3/day) (m3/day)

QRW 18,229.75 51.81 529,381.95 317,629.17

Fig.3. Map of major water users in the QRW

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Domestic Water Use and hope. The QRW streamflow (70%) and groundwater (80%) have been predominantly Domestic water was used primarily used for agricultural purposes. Due to large for drinking, cooking, washing, bathing, and upstream diversions for agriculture and the doing other household chores. It is a basic absence of policies to protect in-stream need required in the QRW. The present flows, QRW flows are routinely low by domestic demand, as shown in Table 3, was midsummer. At that time, groundwater is found to be 10,370.36m3/day based on an tapped via shallow tubewells. As reflected in average per capita daily consumption of Table 4, water for agricultural use is 145L. It was observed that the average daily 172,065.10m3/day. Assuming a 50% requirement per person was influenced by increase in an area planted with crops and his/her standard of living, consumption used for raising animals, agricultural demand habits, and water availability, which means would become 258,097.7m3/day. that consumption levels varied widely. Crop Water Requirements and Irrigation The expected increase in population per unit area proportionately increases with The total water requirement is domestic water demand. In 2025, the distributed unevenly across the study area projected water demand was 13,637.16m3/ with irrigated crops distributed based on day. access to good quality water, topography, micro-climate, land ownership, and zoning. In Agricultural Water Use addition, different crop types require different amounts of water. Likewise, water Ganotisi and Cruz (1996) stressed requirement occurs unevenly across the that water is important to agricultural year, with peak requirements for most crops production. Water availability in the farms occurring during the summer months, can spell the difference between desolation generally coinciding with low rainfall. This

Table 3. The existing and projected domestic water demands from the QRW

Table 4. The existing and projected agricultural water demand from the study area

PRESENT PROJECTED INCREASE IN WATER DEMAND (m3/day) USER DEMAND (m3/day) 10% 20% 30% 40% 50% Agricultural (crops and 172,065.1 189,271.7 206,478.2 223,684.7 240,891.2 258,097.7 animals)

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temporal variation in water extraction for As shown in Table 5, rice (25.31%) irrigation can create problems even if the and corn (19.34%) had the biggest water annual requirement may be within the annual demand. Water on rice farms within the capacity of the resource. One of which is QRW has been used to meet several excessive short-term drawdown in essential requirements. The most important groundwater systems due to the of these include the following: a) preparing concentration of extraction within a short time the land for crop establishment; b) meeting frame. Moreover, drawdown is greatly the evapotranspirational demand of the influenced by aquifers with low atmosphere on the crop yield; and c) transmissivity. Generally, when the discharge maintaining adequate moisture in the soil rate is higher than the recharge rate, it and around the roots to allow uptake of soil would lead to water table drawdown; nutrients. eventually, further extraction of water from lower aquifer may deteriorate the water Meanwhile, even with the advent of quality. modern irrigation technologies, most farmers

Table 5. Crop water demand from the QRW

CROP WATER DEMAND CROP m3/season m3/day Rice 4,352,184.00 43,521.84 Corn (white) 2,494,213.45 33,256.18 Corn (hybrid) 4,035,038.74 47,471.04 Tomato 915,296.60 12,203.95 Garlic 266,640.00 3,555.20 Onion 160,703.20 2,142.71 Eggplant 1,025,032.80 6,833.55 Ampalaya 254,368.80 3,391.58 Pepper (F/B) 1,063,666.65 11,818.52 Mungbean 90,619.20 1,208.26 String beans 197,778.72 2,637.05 Upo 32,978.72 439.72 Tobacco 130,012.81 1,733.50 Cotton 6,071.10 80.95 Sorghum 38,167.00 508.89 Squash 39,361.70 524.82 Patola 10,638.30 141.84 Water melon 5,344.15 71.26 Sweet potato 18,270.00 243.60 Peanut 10,231.20 136.42 TOTAL 1,5146,617.14 171,920.89

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are still using the traditional methods of this water was tied up in agriculture with a irrigation from the QRW. Generally, water is daily demand of 172,065.1m3/day. Moreover, pumped from the river or shallow tubewell present drinking water supply did not pose and delivered to the field through a series of any major problems. Assuming that a 50% PVC pipes. Irrigation time is based on “just increase in agricultural production will occur enough” principle. In the context of in 2025, the projected water demand will potentially-decreasing availability of water amount to 271,734.9m3/day, which is still resources and deteriorating water quality, a lower than the dependable and conjunctive sustainable irrigation scheme is needed. water supply. Groundwater resources are adequate and require only simple Water Requirements of Poultry, Swine, disinfection. However, dependable water Livestock and other Farm Animals from the QRW is a scarce commodity during the dry season, which may create pressure The water requirements of poultry, in the future from the two major competing swine, livestock and other farm animals are users-agricultural and domestic. shown in Table 6. The estimated total daily water requirement is 144.25m3/day. During the dry season, rational water allocation and the balance between supply Dependable Water Supply vs Domestic and demand is needed. All reasonable water and Agricultural Water Demand demands should be met as far as possible.

Table 7 reveals that dependable and Conclusions and Recommendations conjunctive water supply (336,100.84m3/day) Water demand for all uses within the was adequate to meet the rather low demand QRW is 138,865m3/day which, is around 3 (182,435.5m /day). A significant portion of 42% of the estimated Total Resource Capacity of 336,100.8m3/day. This implies that water supply is presently adequate to Table 6. Water requirements of poultry, meet agricultural (172,065.1m3/day) and swine, livestock and other farm domestic (10,370.4m3/day) needs. animals from the QRW Nevertheless, supply is coming under pressure from changing land-use and urban AVERAGE POPULA- development. Land cover has changed TYPE OF USE USE drastically in the QRW, which imposes a TION 3 (m /day) negative impact on its water resources. Broiler 151,034 52.86 Moreover, there is a glaring decrease in the area of inland water from 257.95ha, to Native chicken 1500 0.53 33.50ha which was attributed to the Fighting cocks 300 0.11 increasing water extraction for agricultural uses. Turkey 100 0.06 Swine/Piggery 1500 30.00 Water resources management then is Cow 300 34.50 becoming more important at the QRW as the demand for water increases. Based on the Goats 100 0.80 result of the study, crafting of sustainability Sheep 300 2.40 policies must be prepared to facilitate the Carabao 200 23.00 realization of parallel development plans and programs. It is envisaged that these policies TOTAL 144.25

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Table 7. Dependable water supply vs domestic and agricultural water demand DEPENDABLE & 2025 CONJUCTIVE PRESENT USER 3 PROJECTED DEMAND WATER SUPPLY DEMAND (m /day) 3 (m3/day) (m /day) Agricultural 172,065.1 258,097.7 Domestic 10,370.4 13,637.2 TOTAL 336,100.84 182,435.5 271,734.9

would significantly improve and maintain meso to regional scale J. Water, 6 (10) reliable and adequate water supply for the (2014), pp. 3152–3181 http:// future. dx.doi.org/10.3390/w6103152

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