By
Prof. Orlando C. Gallardo
(Paper presented to the Seminar on “Man and Environment: The Case of Lake Lanao,” August 16, 1991, Mindanao State University, Marawi City, hosted by the Department of Sociology and the Office of the Vice Chancellor for Research and Extension. This paper is an abridge of the work submitted by the author to the 22nd International Post-Graduate Course as a requirement for completion of the course held in Budapest, Hungary from February to July 1991 as sponsored by the governments of Netherlands and Hungary and UNESCO. The original title of the work is “Reservoir Sizing by Transition Probabilities (RSTP) as applied to Lake Lanao Controversy).
ABSTRACT
Environmental concerns have been the subject of increasing importance in both developed and developing countries. These concerns are usually impact studies on man’s usage of environs and consequence of interference with nature. And the Republic of the Philippines, a developing country, is no exception to this trend.
This paper aims to give inputs to the decision makers and to the public in general on the controversy of operating Agus 1 HEP using Lake Lanao as its reservoir. The paper investigated three different drawdowns namely: 1.0 5 meter drawdown, 2.) 1.5 meter drawdown and 3.) 3- meter drawdown in relation to satisfying a proposed 41 MW plant loading or an 81 cms (cubic meters per second) firm flow or an equivalent annual water demand of 2500 MCM (million cubic meter) as stipulated by government regulations and NPC.
The “solution” used in this paper is by stochastic modeling or particularly, Transition Probabilities as first introduced by Moran (1959) and subsequently enhanced for practical usefulness through the efforts of Zsuffa et al (1987). The method is a computer based mathematical modeling and the software requires at least a PC/AT-286 computer.
Results showed that the utilization of the lake is optimized as a 3-meter drawdown. With this value, the lake is highly reliable to meet the said annual power demand. However, it must be emphasized that the lake’s reliability should not deter the decision makers to examine the effects of the lake level fluctuations that have affected the lives of the people and the environment in general. It is proposed that a comprehensive study on the Water Management Balance be conducted properly operate and utilize the lake not only to satisfy a given proper demand but also to consider the different water needs of the people. These needs among others are irrigation, navigation, domestic, religious, fish farming, and recreation. All of these, the author believes must be subject to the desire to preserve if possible, the natural processes of the lake’s hydrology.
I INTRODUCTION
A. LAKE LANAO – AGUS RIVER SYSTEM
Lake Lanao, the second largest freshwater resources of the country has a normal water elevation of 702 meters above sea level with a surface area about 360 sq. km. It is fed and recharged among others by five major tributary rivers namely: Bacayawan River, Gata River, Masiu River, Ramain River, and Taraka River. These rivers contributed 61% of the waters discharging from the lake (Frey, 1968). The limnological study (Frey, 1968) revealed that the deepest part of the lake is about 118 meters and the mean water depth is 60 meters. Its only outlet is the Agus River which cascades 700 meters down to Iligan Bay at a distance of only 36 km. It has a total storage capacity of 21.254 cu. Km. (21,254 MCM-million cubic meter). As compared to most parts of the country, the study area has a relatively cooler temperature with an annual mean maximum and minimum temperatures of 22.8 degree Celsius and 21.7 degree Celsius respectively. Relative humidity fluctuates from 79% to 90%. The average daily evaporation rate of the area is from 1.0 mm/day to 5.0 mm/day (Agus 1 Environmental Impact Studies, May 1989).
Undoubtedly, the Lake Lanao-Agus River system is an excellent source of energy. This fact is recognized by the early and subsequent economic planners of the country. Its importance resulted to the construction of six hydroelectric plants five of which are operational (Agus 2, Agus4, Agus 5, Agus 6, and Agus 7) while the other (Agus 1) is the subject of the controversy and is not (yet) operational.
B. AGUS 1 HYDROELECTRIC PROJECT/PLANT (HEP) CONTROVERSY
The Agus 1 HEP is an underground hydroelectric plant with a rated capacity of 2×40 MW. Its operation demands the rerouting of Lake Lanao’s water flowing from the Marawi Regulation Dam (MRD for brevity) to its power intake structure situated near the dam. The used water is led through a tunnel of about 1.3 km in length to be discharged and used by the downstream hydro plants. Construction of Agus 1 started on February 1, 1979 and was projected for completion after a period of three years. However, it was only in the late part of October 1990 (after more than a decade) that Agus1 was ready for operation. Several factors contributed to the delay and among cited were poor geologic conditions, strong water seepage, bad peace and order conditions, and labor strikes (NPC’s Memo Report for Senate Committee Mindanao Affairs, 1991 – Memo Report 1991 for short). Also, in the realization of the government’s dream to harness the Agus grid potential, the recommendation made by early studies on the river and the lake to construct the MRD at the mouth of the river was earlier completed on May 5, 1977. The dam made it possible then to develop the optimal electric power potential of the high energy stream dropped of 700 meters in a short distance of 36 km. And as Frey’s limnological study concluded (1968), a regulated or controlled release of water from the lake would create a “Stable river discharge of the cost of stability in lake level”. The study also concluded that if such dam would be constructed in the future, it would have “severe economic and sociological repercussions on the region as well as marked influences on the limnology of the lake.
After the completion of the MRD, the changing of the regime from a stable lake with an unstable river to an unstable lake with a stable river began to take its toll. Plains that were normally used for agricultural purposes were often times inundated during the rainy season. Added to this, is the wanton practice of incessant logging in watershed areas that wears out the sponge effect of forest cover during heavy rains which often times result to an unwanted rise of the lake water elevation. Authorities then quickly pointed out that flooded areas were the prohibited zones as covered in the issued order of the late Pres. Marcos (Memorandum Order No. 398. Nov. 1973 – Annex A) that prohibits the people around the lake to construct or plant crops at an elevation of 702 meters or lower. But this decree is contrary to Islamic teaching that free access to natural sources of water is a right of a Moslem community as declared by the Prophet.
The existence of an organized opposition in the realization of the Agus 1 HEP, for practical purposes did not surface during its construction years. It was only during the new dispensation after the ouster of the late Pres. Marcos (1986) that certain sectors of the society began to take another look on the different projects implemented during the strongman’s regime. Increasing availability of information on environmental issues added awareness among the people regarding the importance of environmental impact studies in man’s usage of his environs.
It was along these lines that an organized group of Muslim Professionals who are either concerned citizens or affected public, founded a group called SALAM (acronym for Save Lake Lanao Movement) on October 6, 1990. Days after it’s founding, a non-violent mass demonstration of tens of thousands marched towards the Agus 1 site to register and made known their opposition to the scheduled plant operation by NPC on same month. To make good and enforceable their claims, the group resorted to legal means by filing an injunction order prohibiting NPC to make the final wet test which was granted by judicial court. Thereafter, the waves of discontent and opposition reached national proposition that an injury was conducted by the lawmakers of the country. In sum, what was an environmental question with socio-economic implications, becomes a political question.
Among others, the SALAM group raised the following issues:
1. That the plant is defective, unsafe due to bad construction practice;
2. That the operation of Agus 1 entails more lake discharges and further drawdown by 9 meters (!) and thus
a. Mosques will be farther from the shoreline for their religious practices of washing themselves before entering their house of worship (Ablution ritual) and face possible relocation;
b. There shall be difficulty in availing water for domestic uses;
c. Lower crop production for farmers situated at the lowlands;
d. Harbor and docking facilities will have to be transferred/rebuilt to adjust to new lake level;
3. That NPC has violated government laws relevant to the operation and management of Lake Lanao;
4. That Agus 1 operation and especially the MRD will have tremendous influence on the ecology of the environs and must be stopped and removed respectively.
On the other hand, NPC’s report (Memo Report 1991) to the committee during the inquiry dismissed the issue on bad construction practice by pronouncing that the plant was designed and constructed under internationally accepted norms. With respect to lake discharge, NPC informed the public that Agus 1 operation requires only rerouting of same volume of water that flows out of the MRD and therefore the fear of more lake discharges resulting to more drawdown of lake elevation will not occur. Furthermore, the corporation revealed that “under normal condition, all Agus HEPs are not necessarily operated at their nameplate rating capacity to optimize water usage-measure of energy conservation that apportion load among plants without water spillage. Secondly, plant loading is governed by lake condition: Elevation and inflow”. It also stressed that NPC has not violated recommended minimum elevation of 697 meters or 5 meters below the 702 meters normal water elevation formulated by a task force of the government in 1971 (Annex B). Same task force also recommended that “NPC should as much as possible limit the rate of drawdown of the lake water but in no case should it more than 1.5 meters per year xxx” Annex C). To reinforce further its argument, NPC issued a schematic diagram showing beneficial effect to power load sharing structures when Agus 1 will be operational because the discharge required will be lesser (Annex D). Furthermore, NPC said that it is adopting the recommended maximum drawdown by LAVALIN International (1986) of 3 meters.
As a summary, NPC outlined the following advantages of the MRD and operation of Agus 1 HEP:
A. Advantages of the dam
1. Excess water can be stored for maximum utilization;
2. Minimize flooding around the lake;
3. Minimize flooding along the Agus River;
4. Stable water supply for Agus River user;
5. Control the minimum level of the lake;
B. Importance of Agus 1 Operation
1. Reduction of discharge from the Lake Lanao at the same Agus plants load;
2. Annual fuel savings equivalent to 771,321 barrels of diesel fuel’
3. Avoided power rate increase
II. OBJECTIVES, LIMITATIONS AND SCOPE OF THE STUDY
With all these multifarious issues on the controversy of commissioning the Agus 1 HEP, the author does not wish to provide the answers to all the questions raised nor to be like the biblical king, “Solomon the Wise” and be the judge in the formulation of an acceptable solution but rather to confront the issue only on the following questions-namely:
1. How to reliable is the lake serving as a reservoir to the power production of Agus 1 HEP if the total drawdown as recommended by a government task force should not exceed 5 meters (that is from 702 meters to 697 meters) in a given operational year?
2. Is the 1.5 meter limited drawdown difference between minimum elevation of the current year and minimum elevation of the previous year be sufficiently met? Is the recommendation of the committee realistic?
3. Is the 41 MW share load of Agus 1 HEP be realized without violating the task force recommendation?
From the questions presented, the study shall be based on the data made available by the NPC. Furthermore, existing knowledge on hydrological sciences learned from the 22nd International Post-Graduate course on Hydrology (Feb.-July 1991, Budapest) shall be the basis of any results and conclusions that could be derived. It is wished that the use of data generously provided by the NPC would not lead to the want of objectivity of the paper because after all, it is only the NPC for over fifty years who has religiously monitored and recorded the important parameters of the lake’s hydrology. And lastly it is the author’s wish that this work will serve as a catalyst for the government to pursue a detailed study of the Lake Lanao-Agus River System and to improve the present hydrological network to collect and record the different parameters of the system and perhaps emulate the Hungarian experience.
III AVAILABLE DATA
This paper makes use of the monthly inflow data to the lake from 1948-1990 as collected by NPC. (Annex E). These inflows were mostly the contribution of the five major tributary rivers as mentioned.
The hydro-meteorology data of the Lake Lanao-Agus River System was taken from several studies conducted by the government which were quoted in the Memo Report for Senate Committee Mindanao Affairs, 1990 by NPC.
Frey’s (1968) limnological study of the lake provided a view on the behavior of the system before the construction of the MRD using data during 1932-1940 and 1948-1966 periods (data also provided by NPC). The war years interrupted the recording of data from 1941-1947. This explains partly why this paper merely used the data starting in the year 1948. Moreover, the 1948-1990 (more that 40 years time series data) is accepted in the hydrological practice.
This study does not have a time series data on evaporation. Hence, its effects were not included.
IV METHODS USED
A. MODELING IN GENERAL
One of the most widely used tool relating to the understanding of processes or system that are time dependent is modeling. It deals with the construction of structures which from some aspects to behave similarly to the real object, process or system to be simulated or modeled. It deals with the construction of structures which from some aspects to behave similarly to the real object, process or system to be simulated or modeled. Activity in this field as applied to different scientific or technological problems is so intense that new publications or research works are appearing frequently in journals especially during the last two or more decades. These models could either be physically based or mathematical. Nowadays, the trend is more on the use of the latter. Availability of computer is the major contributing factor to this trend. Another, is its flexibility in changing the parameters of the system which is wanting in a physically based model. And lastly, scale models tend to be more expensive than mathematical models. This development has enable man to base his decision on the expected outcome and thus reducing his dependence on experience and intuition.
In the field of hydrology, the use of mathematical models is gaining popularity to simulate natural hydrologic phenomena which are considered processes or systems that change with time. This usage gives the designer an insight into the behavior of the system under various conditions of planning and operation.
Basically, with respect to the degree of causality mathematical modeling can be either deterministic or stochastic. In the former, it is classified as such if the chance of occurrence of the variables involved in the process is ignored and the model is assumed to follow a definite law of certainty (e.g. hydrodynamic laws and other physical laws) but not any law on probability. Whereas in the latter, it is stochastic process if the chance of occurrence of the variables is accounted and probabilistic concept is introduced.
B. RESERVOIR SIZING
According to purpose, reservoir can be classified as single or multi-purposes reservoir. These purposes are flood control, low flow augmentation, navigation, irrigation, water supply (domestic and industrial), recreation and water power generation.
In the design of reservoir or more specifically in the determination of its yield capacity, methods that were developed can be classified into four main groups, namely:
1. Deterministic methods which use past time series of inflows and demand time series in mass curve analyses;
2. Methods of generalized empirical relationships;
3. Stochastic Modeling Method (also known as transition probabilities matrix method);
4. Methods of System Analysis, such as linear and dynamic programming.
Generally, these four methods of reservoir sizing approach the problem by finding the required capacity of the reservoir and its corresponding reliability of meeting the demand.
This paper uses the third group of reservoir sizing in the subsequent investigation of the reliability of Lake Lanao to meet the power production demand based on a firm flow of 81 cubic meters per second (cms). Specifically, the method of Transition Probabilities as developed by Istvan Zsuffa and Antal Galai of Hungary was used to provide stochastically the behavior of the Lake Lanao – Agus River System. Also, the model was used to “answer” the questions as formulated in Part II of this paper in relation to the 702-697 elevations or 5 meter drawdown elevation, the 1.5 meter limitation and its relation to power production capacity.
C. Overview of the Method of Transition Probabilities to Reservoir Sizing
This method is an offshoot of the theory formulated by Moran in his book, Theory of Storage (1959). Before computers came to widely use, to borrow the words of the publisher (Water Resources Publisher’s Foreword to Zsuffa et al.’s book), “Water storage related problems using Moran’s theory based on transition probabilities between states of stored volume of water in reservoirs have eluded significant applications.” The works of Zsuffa and Galai are important efforts in that direction.
The method as developed, is a computer-based solution of the transition matrix showing the probability of “finishing in my particular state at the end of a time period for each possible initial state at the beginning of that period” (McMahon and Mein, 1978). For particulars, readers are referred to the author’s original work.
V. STATEMENT AND DISCUSSION OF RESULTS
A. On the reliability of the lake when the maximum drawdown should not exceed 5 meters (702 – 697 meters elevation)
The five meters drawdown limitation means that the reservoir capacity is about 1700 MCM. This volumetric capacity was used to determine the lake’s reliability to satisfy an estimated annual power demand of 2500 MCM based on a firm flow of 81 cms when Agus 1 HEP will be operational as defined by NPC.
RSTP model showed that at this capacity the lake is more than able to meet the power demand. Below is a summary of the results:
1. Yield functions in relation to safety in time
The results indicated that even with a capacity of about 1200 MCM the reservoir approaches a probability of safety in time of almost 100% to satisfy the defined demand.
2. Volumetric Reliability
Similar probability values were obtained with respect to volumetric reliability. As in the previous case, same power demand could be easily meet even at a louder capacity of say, 1200 MCM.
3. Behavior functions of the reservoir
The model also showed that there is a very high probability of overflow with almost no possibility of shortage.
B. On the limitation that drawdown should not exceed 1.5 meters per year.
The 1.5 meter limitation of drawdown (that is from 702-700.5), means that the reservoir capacity is about 550 MCM. With the same annual demand, the lake could not possibly meet the required power demand. The following is a summary of the RSTP’s results:
1. Yield functions in relation to safety in time
Results show that it cannot meet the power demand as defined.
2. Volumetric Reliability
Its reliability is also very poor and the reservoir is capacitated only if the demand is less that 2000 MCM. The direct consequence of which will be to lessen the annual power production.
3. Behavior functions of the reservoir
Results described the behavior of the lake having a small probability of the overflow indicating that at a higher demand of the given capacity, the lake may not be able to supply the pre-defined annual demand of 2500 MCM.
C. Three meters drawdown as recommended by a study conducted by LAVALIN International (702-699 meters elevation)
In this case, the reservoir capacity is about 1100 MCM. RSTP model is in accord with the results of the study to meet the power demand of 2500 MCM, below is a concise statement of the results:
1. Yield functions in relation to safety in time
About 90% of the time, the lake can meet the annual power demand of 2500 MCM.
2. Volumetric Reliability
With respect to volumetric reliability, the lake has a 90% probability of meeting the power demand.
Behavior functions of the reservoir indicated that it is highly capable to meet the demand. (Computer printouts of results are available in the author’s original work).
VI CONCLUSIONS AND RECOMMENDATIONS
Using the RSTP model, it can be concluded that both the 5 meters and 1.5 meters drawdowns are not the values that would optimize the operation and utilization of the lake. The former is a case of over sizing and the latter is under sizing. As a possible optimum solution, the three-meter maximum drawdown recommended by LAVALIN international (1986) which NPC would adopt as an operational rule is in agreement with the RSTP model results. With this capacity, the lake can satisfactorily meet the power demand based on 81 cms firm flow or an estimated annual demand of 2500 MCM. Thus the fear of a 9-meter drawdown according to the model is a remote possibility.
However, whether the lake is a reliable reservoir at a 3-meter drawdown or not, the ultimate question lies in the effects of lake level fluctuations to the people around the lake and to the environment in general. Mori (1991) classified the following important environmental influences of dam construction on nature and society:
A. In area around dam and reservoir
1. Micro-climate change
B. At interior of reservoir
1.Water temperature change
2. Turbidity
3. Eutrophication
4. Sedimentation
C. Others
1. Influence on fish
2. Influence on wild life
It is recommended that an institutionalized lake management system be established by the government to oversee the operation and utilization of the Lake Lanao-Agus River System. Jorgensen (1990) particularized that the two most important activities of such management are: Firstly, the management of the lake water itself and secondly, the management of the whole catchment land area. Furthermore, he favored the establishment of a transition zone in relation to lake shore management with specific goals as follows:
1. Maintain the water quality of the transition zone as well as that of the lake;
2. Reduction of erosion;
3. Protection form flood;
4. Provide a buffer zone between human settlement and the lake;
5. Maintain a gene pool of plants and animals;
6. Control insect population;
7. Provide habitats for fish spawning and bird nesting;
8. Provide aesthetic support for human beings.
The establishment of this transition zone or buffer zone, however, a holistic approach is necessary. Among others, it means that in the decision making process of water resources management, individuals or different sectors of the society whose interests are affected should be part of the process. The use of multi-criteria decision method could be helpful (Bogardi and Duckstein, 1991; Ijjas, 1991).
Aside from these, Chow (1964) emphasized that the major objective of water resources development should be to maximize the national welfare or the regional welfare, as the case may be. This goal could be in the form of optimizing economic efficiency, generation of income redistribution, approach full employment, promotion and sustenance of economic growth, and achieve a certain intangible objective such as preserving wilderness area or maintain ecological balance. In the attainment of this, sometimes it is necessary to compromise with each others.
And lastly, the importance of hydraulic energy is well summarized by Yoshihiko Sasaki’s paper (Vienna, 1991) in this wise;
“The remarkable evolution of the techno-civilization in this century has been driven by expansion of the energy utilization. However, the rapid increase of energy consumption mostly supplied by fossil fuels has placed an unprecedented load on the global environment and has brought about environmental problems such as global warming, acid rain and desertification.
Meanwhile, since the oil crisis of the 1970’s, considerable amount of expense and time have been invested in development of alternative energy for oil such as solar heat and wind power. But these technologies have not been established yet, and such more research and development will still be necessary in the future. In this situation, the hydraulic energy that is renewable, clean, and carbon free, is assuming ever-increasing importance”.
REFERENCES
Zsuffa, Istvan and Antal Galai. Reservoir Sizing by Transition Probabilities. Colorado, USA; Water Resources Publications 1987.
Frey. Limnological and Reconnaissance of Lake Lanao, Marawi City, Philippines: Mindanao State University, 1968.
Chow, Ven Te. Handbook of Applied Hydrology, USA: McGraw Hill, 1964.
McMahon, Thomas A. and Russel G. Mein. Reservoir Capacity and Yield. Amsterdam: Elsevier Scientific Publishing Company, 1978.
McCorduck, Pamela. “Twenty Discoveries That Changed Our Lives”, Science 84 5(Nov).
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Agus 1 Environmental Impact Studies, May 1989.
NPC Memo Report for Senate Committee Mindanao Affairs, 1990
SALAM Primer, Marawi City, Philippines, 1990.
Domokos, M. “Hydrology of Reservoir”, Applied Surface Hydrology (edited by O. Starososzky), Littleton, Colorado: Water Resources Publications, 1987.
Moran, P.A.P. Theory of Storage. Methuen and Co. Ltd: London, 1959.
Mori, Hiroshi. “Environmental Influences of Dam Construction on Nature and Society”, Commission Internationale Des Grands Barrages, Vienna, 1991.
Sasaki, Yoshihiko. Reevaluation of Hydraulic Energy to Meet Global Environmental Needs”, Commission Internationale Des Grands Barrages, Vienna, 1991.
Bogardi, J., “Interactive Multiobjective Analysis Embedding the Decision Maker’s Implicit Preference Function”, Lecture Notes, VITUKI, Budapest, 1991.
Ijjas, I., Zsuzsanna Gorozdi and Istvan Abraham. “Computer Aided Decision Making Programs”, Lecture Notes, Technical University of Budapest, Hungary, 1991.
Jorgensen, S.E. and H. Loffler. Lake Shore Management, Vol. 3, International Lake Environment Committee Foundation and the United Nations Environment Programme, Japan, 1970.
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