RESEARCH PAPER ON FLOOD WATER CONTROL FACILITIES

RESEARCH PAPER ON FLOOD WATER CONTROL FACILITIES With a Case Study on Pampanga Delta Development Project and Flood Control Component

In Partial Fulfillment of the Requirements of CE 141: Hydraulic Engineering (Application of Hydraulic Principles in the Design of Water Control Structures

Group Members: BUENDIA, Christian Ray C. QUIAMBAO, Eldrin MASILUNGAN, Chlenessa

FLOOD WATER CONTROL FACILITIES Introduction Flood water control remains to be an underexplored area of water resources engineering in that progress along these lines are limited to traditional flood control methods such as construction of retaining walls and embankments, building of dry dams and strengthening of riverbanks. Potential damage in the eventuality of flood particularly on rivers in proximity of domestic or industrial areas and agricultural lands must be a paramount interest of the civil engineer, as the socioeconomic cost of such destructive occurrences can be so great as to affect the national economy, not to mention the loss of lives and livelihood that attends it.

Fig. 1 Extent of flood damage in Ishikari River in 1981; (inset) Flood blocking road traffic somewhere in Israel.

In the Philippines, the frequency of drought occurrences is brought about by largescale atmospheric phenomena, predominantly manifested in the fact that the country is visited by an average of 20 tropical storms every year, within or without its six-month wet season. This translates to a bountiful experience of severe damages due to extreme flooding and

landslides. Developments in the prevention of such events, however, are hindered by lack of government support and even corruption in the local and nation levels of the government. Just recently, in 2006, a series of super typhoons hit the country. The destruction caused by typhoon Milenyo in Southern Luzon, typhoon Reming in Bicol Region and typhoon Seniang, is estimated to reach a total of 7.8 billion. Thus, more development thrust to minimize the private and public costs of flood damages, including research and extension works, is very much in order. Causes and Effects of Floods Various factors can produce floods, namely, heavy precipitation, strong winds, unusual high tides, tsunamis, and the failure of water-retaining structures such as dams and retention ponds. Some rivers also experiences periodic flooding such as the Nile River in Egypt and the Mekong River in China. Aside from damages on properties and the loss of lives, flooding can also bring about environmentally unsafe occurences such as erosion of the soil due to intense rainfall on a small area or on a supersaturated soil. Erosion of oil can become a precursor of sedimentation in rivers and other bodies of water downstream. Flooding can also interfere with traffic and cause structural damages on bridges, sewer lines and bank lines. Flood Control Facilities A.) Flood Control by Reservoir/Dams

A flood control reservoir or dam temporarily stores flood portions in order to minimize flood peaks. It is usually situated at upstream, and water discharge is located downstream. Dams are large structures specifically built across a stream or a river to retain large amount of water. It allows for a controlled release of water during times of flood and even drought. One type of dam is called the dry dam, which is contains no gates or turbines and allows free-flow of channels during normal conditions. There are reservoirs called multipurpose reservoir that have multiple functions such as irrigation, hydropower generation and flood control. The following are the various types of dams as describe by Chanson (2004): Arch dam- Dam in plan dependent on arch action for its strength.

Buttress dam- A special type of dam in which the water face consists of a series of slabs or arches supported on their air faces by a series of buttresses. Crib dam- Gravity dam built up of boxes, cribs, crossed timbers or gabions, and filled with earth or rock. Cyclopean dam- Gravity masonry dam made of very large stones embedded in concrete. Diversion dam- Dam or weir built across a river to divert water into a canal. It raises the upstream water level of the river but does not provide any significant storage volume. Earth dam- Massive earthen embankment with sloping faces and made watertight. Gravity dam- Dam which relies on its weight for stability. Normally the term ‘gravity dam refers to masonry or concrete dam. Hydraulic fill dam- Embankment dam constructed of materials which are conveyed and placed by suspension in flowing water. Masonry dam- Dam constructed mainly of stone, brick or concrete blocks jointed with mortar. Rockfill dam- Embankment dam in which more than 50% of the total volume comprise compacted or dumped pervious natural stones. Weir- Low river dam used to raise the upstream water level (e.g. Plate 8). Measuring weirs are built across a stream for the purpose of measuring the flow.

(a)

(b)

Fig. 2 (a) Flood control structure model (b) Bibai Dam, a gateless system of improved dam construction for efficient management.

Dams have been used for many centuries to serve as water reservoirs for irrigation and other domestic uses, as well as to be a source of hydroelectric power. It was only recently that it was used as a flood control device. Meanwhile, constructing a coordinated group of dams and reservoirs on the headwaters of the streams that lead into the main rivers is an effective method of controlling floodwaters, since water can be stocked up during periods of heavy runoff and released gradually during dry seasons or droughts. There are also dams that are engineered to provide levels of protection at par with those provided by permanent flood defense methods but have the distinct advantage of being removable when not required. Such methods greatly contribute in preserving the integrity of the landscape and architecture of the area and can be used between existing structures such as roadways, subways, embankment promenades, industrial complexes and shopping precincts. This type of dam is designed to be completely self-supporting over almost any distance with specifications for virtually any height of floodwater. One practical use of a dam as flood water control facility can be seen on the Humber River in Toronto where a weir was built to prevent a repeat of the flooding caused by Hurricane Hazel in 1954 which destroyed nearly two fifths of Raymore Drive. B.) Flood Control by Channel/River Improvements

Fig. 3 Preservation of Kushiro River and Kushiro Swamp in Japan.

Another way of controlling flood is improving the channel or river by increasing the discharging capacity of the stream, resulting in the decrease of the duration and height of the

flood. By increasing the cross-sectional area of the channel or by increasing the velocity of the water flowing in the stream, the flood carrying capacity of the said river can be significantly increased. In this aspect of flood control, the fact that the hydraulic mean radius of a channel increases with increasing depth, and thus increase the velocity, makes a deeper channel more preferable than a wider channel. From the design of open channels one knows that the channel velocity is affected by hydraulic mean radius, slope of river bed and the roughness of the bed and sides. The following are some of the recommended measures by Tushar (2007, 2008) in order to reduce roughness and therefore increase water velocity: 1.) removing sand bars 2.) prevention of cropping on river beds near banks 3.) removal of fallen trees and other snags 4.) elimination of sharp bends of meanders by providing cutoffs.

Floodways are constructed on the lower reaches of rivers to divert floodwaters. Certain areas are allowed to be flooded to prevent the flooding of areas presumably more prone to economic and social loss than the flooded areas. This is achieved by widening the river at certain portions of the flow, whereby water is permitted to overflow. Such method of flood control has been used by the Egyptians (Nile Valley) and the Chinese (Mekong River) for thousands of years already. In these areas, the continued fertility of the soiled near the river is dependent on the periodicity of the flooding, since the soil deposited by sedimentation from floodwater is very rich in various nutrients needed by crops. An example of the application of floodways is shown by the elaborate system of floodway defenses used in province of Manitoba in Canada. Passing through this region is the Red River whose mainspring flows from the United States northward and then traversing the city of Winnipeg and into Lake Winnipeg. Such north-flowing rivers is subjected to periodic rise in water levels when the snow melts in the southern sections of the river, thus resulting in destructive flood downstream as in the case during the spring of 1950. Massive flood control systems such as diversions, dikes and floodways were then constructed in order to prevent the recurrence of extreme flooding in the future. This foresight from the government checked the catastrophic effects of the 1997 flood that hit several communities upstream of Winnipeg such as Grand Forks, North Dakota and Ste. Agathe in Manitoba.

C.) Flood Control by Construction of Dikes and Flood Wall

Another method of flood control is the construction of dikes, levees or floodwalls along the riverbanks.

Fig. 4 Adjoining seawall protecting a line of residences; (inset) Overtopping waves attacking national highway No. 36 (Shiraoi Bypass).

Levees are economical, direct and immediate flood control method similar to earth dams in the sense that these are earthen embankments which are raised parallel to the river either on either sides or one side of the river. These are constructed beyond the meander belt of a river and prevent a river from altering its course. One demonstration of the effects of the failure of levees is exemplified when the levees and flood gates constructed in the New Orleans Metropolitan Area in the United States, which has 35 percent of its area located below sea level, suffered from numerous breaks during the destruction left in the wake of Hurricane Katrina. The disaster left half of the Metropolitan Area, including the city proper and the eastern section of the Metropolitan area, in flood ranging from a few inches to twenty feet in coastal communities.

Dikes can also be constructed as another method of flood control. Dikes help prevent damage due to floodwater and can lower the risk of having floods relative to other methods. Usually, dikes are used in conjunction with other flood control systems in order to offset the risk of having the dike collapse due to floodwater. On of the classic examples of flood prevention through the use of dikes, and also the largest and most elaborate flood defenses, can be found in the Netherlands. Dubbed as the Delta Works or Delta Plan, with the Oosterschelde dam as its centerpiece project, it has one of the world’s largest dams, the Afsluitdijk (which closed in 1932) located in the north of the country. Constructed in 1958 and completed in 1985, the project consists of a series of giant dams linking Rhine, Maas and Schelde river deltas. The structures in the said project were built in response to the North Sea flood of 1953, in the southwestern part of the Netherlands. A remarkable feet of the Delta Plan is the construction of huge storm-surge barrier 9 km (5.6 mi) long. This structure is lowered only when a sea flood is anticipated; otherwise, tides move freely through the passage. Flood barriers with variable height can also provide total flood protection in buildings while preserving the aesthetic integrity of the building. Flood barriers are used to shelter house doors, windows, driveways and garages in business premises such as shops and stores, homes and retail outlets. D.) Flood Control by Drainage Dredging as well as the setting up of pumping stations located at the main exits of the drainage pipes behind embankments is also one means to control floodwater levels, especially in agricultural lands. Drainage pipes are used to pump off rainwater that cannot be drained off by gravitational force within a specific region or area. Drainage is important for sustainable agriculture. It is imperative that an efficient drainage system be coupled with the existing irrigation to avoid negative impacts on agricultural production and soil caused by floods. The following are the functions of a good drainage system: (1) it protects the resource base for food production; (2) it sustains and increases yields and rural incomes; (3) it protects irrigation investment; (4) drainage infrastructure serves rural and urban residents as well as industry; (5) it protects human lives and assets against flooding and high groundwater levels; and (6) drainage services improve health conditions.

Case Study: Pampanga Delta Development Project and Flood Control Component The lower basin of the Pampanga River is one of the areas in the province which experiences frequent flooding. The Pampanga Delta, a swampy lowland area at the mouth of the Pampanga River, is visited frequently by typhoons which cause flood, resulting in considerable damage to the farming and fishing industry of the region, aside from loss in public and private property. Although flood control projects has already been done in the river since 1939, the development potential of the lower basin particularly in aquaculture necessitates serious attention being devoted to flood control systems, especially as the Pampanga River has limited flow capacity because of the 0-9 m above sea level elevation of the delta.

Fig. 5 Map of area in which flood control facilities were constructed.

The objective of the project was to “enhance flood controls on the lower basins of the Pampanga River in Central Luzon, an area prone to perennial flooding, by implementing river improvement works, thereby contributing to improvements in living standard and to regional economic growth. The project covered an area of 100 km 2 within the Pampanga Delta and benefited approximately 70,000 people.

The project was an offshoot of the five-year Medium-Term Philippines Development Plan conducted in 1988 to 1992 by the Department of Public Works and Highways (DPWH). The Medium-Term Philippines Development Plan stipulated that priority attention should be given to mitigating natural disasters. Phase 1 of the Pampanga Delta Development Project (PDDP: flood control component) was given a high priority undertaking involving implementation of river improvement works corresponding to a 20-year return period flood probability. The five-year Medium-Term Philippines Development Plan for 2004 to2010 in the same way gives priority attention to mitigating the effects of natural calamities and retained the priority status for improvements of Pampanga River’s infrastructure and water resources management.

Fig. 6 A newly built road dike.

Various problems, however, were encountered during the fulfillment of the project plan. Among these is the shortening of the dike construction from the original 22.7 lm to only 15.4 km due to high bid prices coupled with budgetary constraints. The DPWH also devised resettlement plans for local residents near the river and started providing them with project information through local government officials. Some of the residents, however, opposed to resettlement thereby reducing the length of dikes further reduced to 14.2km (right bank) and 13.2km (left bank). Dredging and related construction works were also reduced along with this decision.

The project was also delayed for 72 months and took approximately 1.9 times of the planned project period. The delays occurred during the construction phase and were attributable to budgetary constraints as a suspension of works from October 1993 to April 1995 occurred. Another work suspension from December 1999 and extended for over a year resulted from difficult negotiations with residents of Calumpit on land acquisition, as well as a dredger accident caused by fire and leakage. Prior to the completion of the project, the beneficiary areas had suffered from flooding with an average depth exceeding 100 cm. Resident survey of 150 people shows that all respondents living on the left bank stated that their property has been inundated since project completion, while this held true for 40 percent of respondents living on the right bank. The following are the benefits that resulted from the construction of flood control facilities in the Pampanga River: 1.) Changes in awareness of flood damage among local residents 2.) Results from the beneficiary (residents) survey show that 69 percent of residents

living on the left bank and 78 percent of residents living on the right bank have recognized a decrease in the frequency of flood as compared to pre-project levels. 3.) Results from the beneficiary (residents) survey show that 56 percent of residents

living on the left bank have experienced less serious flooding damage as compared to pre-project levels. By contrast, 77 percent of residents living on the right bank, including 55 percent who stated that they had experience no damage or considerable decrease since the completion of the project, stated that the extent of damage has decreased as compared to pre-project levels. 4.) According to results from the beneficiary (residents) survey, the majority of

respondents living on the right bank (80 percent) where damage due to the incursion of river waters has decreased are worried about flooding, but say that they have fewer concerns since the project was completed, while 75 percent of respondents living on the left bank stated that their concerns have abated, despite the continued occurrence of flooding. 5.) Results from the beneficiary (residents) survey show that many respondents living

on the right bank (83 percent) were aware of vulnerability to flooding as a risk to/constraint on their ability to continue pursuing livelihood activities. Since the completion of the project, 89 percent of these residents stated that this risk has been reduced. On the other hand, 91 percent of respondents living on the left bank stated that they were cognizant of this risk, with 86 percent recognizing a post-

project decrease (however, 51 percent stated that there had been only a marginal reduction in sflood-related risk). 6.) In results from the beneficiary (residents) survey, the improvement in sanitary

conditions over pre-project levels had been felt by 79 percent of respondents living on the right bank, with 59 percent considering this improvement impact of the project. Moreover, 46 percent of the residents who recognized improvement in sanitation had felt a substantial reduction in the incidence of waterborne diseases. By contrast, 63 percent of respondents from the left bank stated that there had an improvement in sanitary conditions, with 17 percent attributing this to the project. 7.) On access to cities and municipalities, which has a substantial effect on livelihood,

81 percent of respondents living on the right bank stated that there has been an improvement as the result of the development of dike roads (of which 57 percent cited a major improvement). On the left bank, 71 percent of residents stated that access had improved (with 21 percent citing a major improvement). Residents on the left bank urged the early completion of dike for more convenient transportation in the region, pointing out that the dike road developed by the project does not connect with any public highways (because of the shorter length of dike).

References Daugherty, et al, Fluid Mechanics with Engineering Applications, SI Metric Edition, McGraw-Hill Book Co., 1989 Streeter and Wylie, Fluid Mechanics, Seventh edition, McGraw-Hill Book Co., 1979 Vennard and Street, Elementary Fluid Mechanics, Sixth edition, John Wiley & Sons, 1982 Chanson, Hubert, The Hydraulics of Open Channel Flow: An Introduction, Second edition, Elsevier Butterworth-Heinemann, 2004 U.S. Army Corps of Engineers, Earth and Rock-fill Dams - General Design and Construction Considerations (Engineering manual), 1994 Chow, V. T. Open-Channel Hydraulics. Mc Graw-Hill Book Co., 1959 Tushar, Mori N. A Seminar Report on Estimation and Control of Flood, 2007-2008 http://en.wikipedia.org/wiki/Flood_control http://encarta.msn.com/encyclopedia_761561222_2/Flood_Control.html http://www.mlit.go.jp/hkb/river_e.html http://www.articlesbase.com/college-and-university-articles/an-article-on-flood-control138104.html http://www.neda5.net/updated_rdp/chapter22_irrigation.htm