Not: Figürlerin, Tabloların ve Formüllerin daha yüksek çözünürlüklü görüntüleri için görsele sağ tıklayıp “resmi yeni sekmede aç” seçeneğini seçiniz
PROF. DR. AHMET SAMSUNLU
ISTANBUL TEKNİK ÜNİVERSİTESİ İNŞAAT FAKÜLTESİ ÇEVRE MÜHENDİSLİĞİ BÖLÜMÜ MASLAK/ISTANBUL
Özellikle gelişmekte olan ülkelerde, nüfusun hızlı artması ve göç nedeniyle kentleşme olayı hızla gelişmektedir. Bu beklenmedik nüfus artışı kentlerin etrafında gecekondulaşmayı yarattığı gibi mevcut yerleşim bölgelerinde de yüksek yapılar inşa ederek, konut sorununa çözüm bulabilmek için, hazırlanmış olan imar planları sık sık değiştirilmektedir.
1950’lerde nüfusu 1 milyon civarında olan Istanbul’un bugün nüfusu ise 14 milyon civarında olup, bu süre içinde hem gecekondulaşmanın hem de yüksek yapılaşmanın yaşandığı bir şehir olmuştur.
Bu şekilde bir gelişme sonucunda kentsel altyapı olarak tanımladığımız içme ve kullanma suyu tesisleri, atıksu şebekesi, yağmur suyu uzaklaştırma sistemi, temiz ve pis su arıtma tesisleri, çöp bertaraf tesisleri, yol, elektrik, haberleşme hatları ve gaz sistemleri hızlı inşa edilememekte veya yetersiz kalmaktadır.
Bu tebliğde yapılan plan değişiklikleriyle artan nüfus yoğunluğunun mevcut altyapı tesislerinin yetersiz kalması, içme suyu ve kanalizasyon şebekelerinde yaşanan sorunlar yanında su basıncı ve su kayıpları problemleri genel olarak Istanbul örneğinde incelenecektir.
Anahtar Kelimeler: Kentleşme, Yüksek Yapılar, Altyapı Sorunları.
TALL BUILDINGS AND INFRASTRUCTURE PROBLEMS IN CITIES
PROF. DR. AHMET SAMSUNLU
ISTANBUL TECHNICAL UNIVERSITY FACULTY OF CIVIL ENGINEERING ENVIRONMENTAL ENGINEERING DEPARTMENT MASLAK / ISTANBUL
Urbanization is rapid due to rapidly increasing population and migration in especially developing countries. This unexpected increasing population causes squattering around the city as well as changes in the zoning and construction planning frequently by constructing tall buildings in the available settlement places.
In 1950’s Istanbul had a population of 1 million and today the population is around 14 million. In the meantime, both shanty and tall structuring has occurred in Istanbul.
As a result of such a development, the urban infrastructure which we define as drinking and using water treatment plants, wastewater network, rainwater drainage systems, waste disposal plants, roads, electric and communication lines and gas distribution cannot be constructed quickly or it has been insufficient.
This paper examines the water pressure and water loss in general and through Istanbul example besides handling the current infrastructure insufficiency with increasing population and restoring of drinking and wastewater network
Keywords: Urbanization, Tall Buildings, Infrastructure Problems
The habitability and high living quality of cities depend on the well planning of the technical infrastructure in cities. Technical infrastructure in cities includes structures of water supply, wastewater disposal, transportation, electricity, natural gas, communication, etc. However, only water and sewerage systems are handled as a part of technical infrastructure and defined as urban infrastructure in this paper.
While preparing city plans, number of house floors and the population density is defined. In such planning tasks, buildings with fewer floors are preferred to enable comfortable way of moving for people and easy access to their residences. Today in Europe, residences higher than 5-6 floors are not preferred and are often constructed as social structures. Therefore city planners choose to include buildings with fewer floors in their planning works. Water supply and sewerage systems which are crucial elements of urban infrastructure are designed according to these plans. In locations planned with this understanding, water rises up until the top floors with the pressure of the network. This is the most economical solution in engineering terms.
The population of Istanbul today which was around 1 million in the 50s is approximately 14 million. This period in between has witnessed both slum areas and construction of higher building. Table 1 shows the population and increase in Istanbul.
Table 1. Population in Istanbul in Years and the Annual Increase Rate of the Population
|Year Population Annual Increase Rate (%) 1914 909.978 -0,27 1927 680.857 -2,21 1935 741.148 1,07 1940 793.949 1,39 1945 860.558 1,62 1950 983.041 2,70 1955 1.268.771 5,24 1960 1.466.535 2,94 1965 1.742.978 3,51||Year Population Annual Increase Rate (%) 1970 2.132.407 4,12 1975 2.547.364 3,62 1980 2.772.708 1,71 1985 5.475.982 14,58 1990 6.629.431 3,90 2000 8.803.468 2,88 2009 12.782.960 4,52 2010 13.120.596 2,64 2011 13.483.052 2,76|
Tall buildings are built instead of lower buildings in such planned areas due to population increase and urbanization particularly in developing countries. The water pressure shall drop due to the consumption increase in the water network and buildings nearby shall be affected. Due to buildings designed in this manner, the existing water and sewerage networks prove insufficient and even fail to meet the demand. In order to transfer water to such buildings, either an increase in the existing network’s pressure or a new, large-diameter pipeline that connects to the main network is required.
In cases of tall building constructions in regions with lower buildings, Istanbul Water and Sewerage Administration (İSKİ) demands the required pressure maintained with hydrophore if the water flow is insufficient in related regions. When the flow proves insufficient in network size, new pipes are laid and sufficient flow is thus provided. The same is applied to the sewerage network as well.
Pressure allowed in water networks has to be maintained within a limit to minimize the water loss and breaks of water pipes. Furthermore, in order to avoid fast breakdown of water fixings, the pressure has to be maintained within certain limits. An increase in network pressure due to tall buildings may cause the mentioned problems to occur.
2. TALL BUILDINGS AND INFRASTRUCTURE SYSTEMS
While no certain definition is found in our country, in certain countries like Germany, buildings taller than 22 meters are considered as “tall building” (skyscraper). These structures sometimes host around 1000-4000 people. The fact that tall buildings are point sources when it comes to water and waste water causes a sudden overload in these systems. The water demand of this many people is half the flow in a ø 100-150 mm water pipe laid under streets of lower buildings during the peak water consumption hours. A similar overload is also an issue in sewerage systems. In such regions, the sewerage pipes are chosen as 200 mm.
Tall buildings planned for areas with lower buildings shall cause insufficiency of pipes for water pipes used for water supply and for sewerage pipe used for waste water disposal.
2.2 Drinking Water System
As we know, pressure of drinking water systems is as important as the water amount in these networks. In ideal cases, water needs to be supplied to top floors of all buildings in a city via the network pressure. This is clearly the most suitable and economical solution in engineering terms. Otherwise many buildings like in Istanbul need to be fed via pumping and hydrophore systems. In such cases the operation and energy costs alongside the investment costs shall rise up to high amounts.
Water pressure value in the pipe within drinking water networks is limited as maximum and minimum. Ideally a minimum of 30 mss water pressure is required to provide ample supply of water to every subscriber from the urban water network. Both the İller Bank (Bank of Provinces) and İSKİ take this rate as the basis in drinking water terms and conditions. The maximum pressure allowed in the network is 80 mss. In a higher pressure rate pipe breaks at addition points of the pipes shall lead to higher rates of water loss. Due to the minimum and maximum pressure values, drinking water Networks are fed via 50 m altitude ranges and Networks (services). In these ranges, lower altitudes in the city will have high water pressure while higher altitudes will have lower water pressure (Samsunlu, 1986). Another reason to this application is that the water equipment in houses is produced for an optimum of 50 m of water pressure (KORDA, 2005).
Figure 1. A Two-Floor Network Model
Even when the network pressure is at an ideal rate in case where tall structures are constructed on high altitudes, it is possible to feed only a certain part of a building with network pressure. Such an example is shown on Figure 2.a. In order to feed the higher floors of the building pressure increasing systems such as hydrophores are required. This brings along additional operation cost and energy consumption and also provides an unfair superiority to the building in terms of making use of the water network. In case where in which is given from a water tank at the ground level to higher floors with a hydrophore or direct water intake from the network with a pump, this building has a chance to receive more water compared to buildings fed through regular ways. Furthermore it should be noted that on high points of great cities like Istanbul the water pressure in the network falls below 30 m. On the other hand, as seen on Figure 2.b, when the tall building is constructed on a lower altitude it becomes more convenient for the drinking water network. On condition that there is adequate water in the network and that the targeted pressure is provided, a 80 m tall building (around 25 floors) can be fed from the network via gravity. Furthermore, in case the network pressure falls due to various reasons, the tall building is affected same way other buildings do. As seen from this example it is more appropriate to construct tall buildings at low altitude locations of the city as far as water network is considered.
Figure 2. Tall buildings in drinking water networks
2.2. Sewerage System
As we know, the water flow in sewerage systems is free surface. This makes the water flow in the same direction of and often parallel to the ground elevation. Therefore the channels in sewerage systems are directed from higher altitudes to lower ones.
Figure 3. Tall Buildings in Sewerage Systems
As seen in Figure 3, in case a tall building is built onto a high altitude in the city, the flow rate and diameter of the road channel that will receive the wastewater of that building shall be designed according to the flow rate of the tall building. In such a case, the channel diameter shall receive a large value from the beginning. As is the example in Figure 3.b, in case when a tall building is built on low altitudes, the road channel will have a small diameter from the beginning and the diameter increases only after the tall building for a limited distance. When these two cases are compared, it is seen that the channel cost is higher in the first case. In terms of sewerage network, it is more appropriate to construct the tall building at low altitudes.
If tall buildings are constructed within settlement areas with completed infrastructures, these systems shall be insufficient. The water pressure shall decrease due to the increase of water consumption in the water network and the buildings nearby shall be affected. The capacity of the sewerage system shall be overloaded and the environment shall be polluted by channel flooding as the basement floors. The reason for this flooding is that there is pressure increase and water pressure is high in the channel.
3. INFRASTRUCTURE PROBLEMS IN URBAN AREAS
The economical lifetime of infrastructure facilities is between 20 and 50 years. Therefore they are planned according to the needs of the 30 years ahead. However, as is the case in developing countries, population movement from rural areas to urban areas and population increase is rapid. One of the most important steps of planning and projection of infrastructure facilities is the well assumption that the population these facilities will serve in its lifetime. It is known from previous experiences that long term population assumption in developing countries is hard. An example could be that the Master Plans made for Istanbul reaches the assumed amount of population so rapidly that these Plans are continuously revised. Therefore, the infrastructure services in mega cities like Istanbul always stay behind the settlement density.
On the other hand, the scarcity of estate and the revaluation of downtown estates have brought the consequence of the demolishing of fewer floor buildings to construct tall buildings. At this point, there appears a new dimension to the infrastructure problems that appear due to rapid urbanization and slum settlements. This is the inadequacy of infrastructure that appears in downtown areas with complete infrastructures due to this re-settlements. For a solution to these problems, there is need for renovation and addition to the drinking water and sewerage networks. Besides the costs, there is also a challenge of conducting construction in an existing settlement area.
One of the main infrastructure problems on particularly drinking water is the skyscrapers built on the high locations of the city. Around 40 skyscraper constructions on high altitude areas such as Levent, Mecidiyeköy and Yıldız have caused significant problems on water and sewerage systems. As an example, the project titled “Research on Fire Security and Protection from Fire” prepared by Istanbul Technical University to Istanbul Metropolitan Municipality (İTÜ, 1989) can be stated. The project shows that the isobars of the water network of Beyoğlu region that includes Levent, Mecidiyeköy and Beşiktaş have shown that the water network pressure has gone below 10 m and in certain points have reached as low levels as 0 (Samsunlu, 1992).
4. THE RELATION BETWEEN WATER PRESSURE AND WATER LOSS
It is known that there is a relation between pipe breaks, bursts, water loss in water and the water pressure in the network. While designing water Networks, maximum and minimum pressure is taken as basis. This value is often between 30 – 60 meters and exceptionally 20 – 80 meters. As the pressure increases, the loss in the network similarly increase. The network loss values are between 5 – 15 % as standard. In undeveloped countries, this rate is as high as 52 %. The rate in Istanbul has been decreased to only % 26 from % 50 with precautions taken and renewal of pipes. Figure 4 shows the rate of water loss within years. In developed countries, this rate is even below the standard level. For instance Berlin has a water loss rate of 2 %.
Figure 4. Water Leakage and Loss in Istanbul
A study in Australia has revealed that pressure control management has an effect on prevention of pipe breaks that may occur on decreasing the existing leakage in settlement areas (Lambert and Waldron, 2010).
Figure 5. Effect of Pressure Control Management on Frequency of Pipe Breaks
As can be seen on Figure 5, upon the pressure control works conducted, the breaks and bursts that occur upon mains have decreased 56 % and on the service lines 73 %. While before the pressure control the mains had 50 breaks a month, less than 10 breaks occurred in a month after the pressure control. This clearly shows how the pressure in pipes affects the pipe failures and therefore the pipe losses.
Protecting the regions with fewer floors in terms of life quality enables proper functioning of the infrastructures planned or constructed. Tall buildings to be constructed on these areas later on shall cause inadequacy of existing infrastructure systems. It also shall cause loss and leakage in water networks and basement flooding in sewerage Networks. Therefore plans need to consider protection of older parts of the city while foreseeing tall buildings in new settlement areas.
Tall buildings for fewer floor buildings require an increase in pressure and therefore require pumping and hydrophore facilities. This will cause unfair access to network service. Furthermore, the construction of tall buildings shall become inadequate and require renovation of older water and sewerage networks, thus, new costs shall arise.
Tall buildings bring along a number of technical infrastructure advantages if constructed on low altitude locations of the city. Since the required pressure is provided from the network, there shall be no cost of hydrophore and pumping. However, new sewerage pipes shall not be big in diameter, only at the tall building there will be a slight increase in diameter. Construction of tall buildings in high altitudes of the city shall bring along cost increase and other challenges.
Due to tall buildings in water networks, problems occur at networks and fixings when the pressure is increased. Therefore water shall increase the loss by bursting through the broken points of pipes and cause a bigger leakage. Furthermore, pressure control tasks on pipes shall decrease damage to the pipes as well as the leakages.
- Samsunlu, A., (1986) “Water Supply”, Dokuz Eylül University, Faculty of Engineering and Architecture
- Korda, M., (2005) “Staedtebau”, Teubner Verlag
- Boduroğlu,H., Samsunlu, A., et al. (1989), Istanbul Metropolitan Municipality, Research on Fire Security and Prevention of Fire, Water Resources and Fire Plugs ,Construction and Environment Group, Vol. 9 ,İTÜ.,
- Samsunlu, A., (1992) Tall Buildingd 2nd National Symposium, İTÜ Faculty of Architecture, Istanbul
- Lambert, A. and Waldron T., (2010) “Management Australia’s real loss levels”, Water21