Scientific Procedures Applied to the Planning, Design and Management of Water Resources Systems (Proceedings of the Hamburg Symposium, August 1983). IAHSPubi. no. 147.
Goals and management of the Ruhr reservoir system since the beginning of our century
F, W, RENZ Ruhr Reservoir Association, Kronprinzenstrasse 37, D-4 300 Essen 1, FR Germany
ABSTRACT In the last 85 years a system of reservoirs has provided augmentational low flows in the Ruhr drainage area. The necessary discharge of the reservoirs compared with the water losses of the basin (i.e. the amount of water pumped over the watershed into adjacent areas for public water supply and the losses due to evaporation within the Ruhr basin) gives the gross efficiency rating of the reservoir system with respect to the goals of water management. The periods when parts of the reservoir system are not fully available for water manage ment are presented as a duration curve. Moreover the predicted water demand in the Ruhr area is compared with the measured amount. Today, the time which is needed to introduce a new reservoir within the system is longer than the period of time for which reliable forecasts of water demand are possible.
Objectifs et aménagement du système de réservoirs de la Ruhr depuis le début de notre siècle RESUME Au cours des 85 dernières années, un système de réservoirs a été réalisé sur le bassin versant de la Ruhr en vue d'augmenter le débit de basses eaux. Le débit sortant exigé des réservoirs comparé aux pertes en eau du bassin (c'est à dire le volume d'eau pompée dans le bassin vers les zones voisines pour la fourniture d'eau au public et les pertes par evaporation dans le bassin de la Ruhr) conduit au calcul de l'efficacité globale du système de réservoirs par rapport aux objectifs de l'aménagement des eaux. Les périodes de temps au cours desquelles certaines parties du système de réservoirs ne sont pas disponibles pour l'exploitation des eaux sont présentées comme courbe de durée. En outre la demande prévue en eau est comparée avec la dernière valeur mesurée du volume d'eau qui a été utilisée. Actuellement le temps nécessaire pour aménager un nouveau réservoir dans le système est plus long que la période de temps pour laquelle il est possible de donner une prévision valable de la demande en eau.
I PRODUCTION
The subject of this paper is the water management system in a highly industrialized area in the Federal Republic of Germany (FRG). In the last decades of the nineteenth century coal mines and steel 637 638 F.W.Renz production developed in a formerly rural area. In 1899, steel production in this district was 4.6 times higher than in 1880. In 1899, only in the USA and England was more coal produced than by the Ruhr mines. In the first years of our century, the first steps towards today's water-management system were taken. Only five years after the foundation of the Ruhr Reservoirs Association in 1899, four reservoirs were completed for low-water augmentation of the River Ruhr (Renz, 1980). The water works pump the necessary water from the Ruhr into adjacent areas. Nowadays about 5 million people are supplied with water from the Ruhr. These 5 million people comprise about 8% of the total population of the FRG and are living in only 2% of its territory. The area is today, as well as 80 years ago, an area of heavy industry. Sixty percent of the coal, 40% of the steel, and 17% of the energy of the FRG are produced here; chemical, glass and car production are also to be found. Moreover an important part of the German brewery capacity is located here. Only a small amount of light industry exists (Londong, 1978). In this highly industrialized area called "Ruhr Revier" an amount of water equal to 75% of the mean annual rainfall is needed to supply the population and industry. Therefore it is necessary to pump water of good quality from other drainage basins into this district . For more than eighty years this water has been mainly drawn from the River Ruhr. Today a complex water management system exists, which comprises several subsystems, e.g. cooling water for energy production is today taken from the River Lippe in the north of the area and from shipping canals; during critical dry periods water is also pumped from the mouth of the River Ruhr; part of the demand for water of good quality is nowadays supplied by groundwater, which is pumped from the north into the district of high population density. Until now the water of the River Ruhr has been the basis for supplies for both domestic and industrial consumption.
NATURAL RUNOFF AND WATER DEMAND
2 The mainly forested drainage basin of the Ruhr (4488 km") is hilly and a part of the so-called "Rheinisches Schiefergebirge" (Rhenish Slate Mountains). This type of rock is not very suitable for infiltration and storage of groundwater. The aquifers are mainly restricted to river valleys with layers of sand and gravel over an impermeable formation. The runoff of the Ruhr can decrease to 3—1 3—1 3.5 m s during extreme low-flow periods and increase to 2000 m s during floods. The average runoff for the period 1927/1981 is 78.3 m3s_1 or 2450 m3xl06year_1. The extent of human influence on the water cycle on the Ruhr is indicated by a comparison of the 3 P observed lowest annual runoff of 1316.6 m xlO" in 1964 to the 3 6 — 1 average water abstraction of 900 to 1400 m xlO-year In contrast to some other districts in Germany, e.g. the water supply system of the Harz reservoirs, the water for public water supply in the Ruhr district is not taken directly from the reservoirs by pipelines, but indirectly transported by the River Ruhr to the water works. The water discharged from reservoirs is used for a Management of the Ruhr reservoir system 639 variety of purposes (cooling, energy production etc.). The main water works are located in the lower and medium reach of the Ruhr (Imhoff & Mantwill, 1980). Except for dry periods the water demand can be covered by the natural runoff of the drainage basin. In dry periods the minimum runoff in the River Ruhr, which is necessary for the water works, is guaranteed by water discharged from the reservoirs of the Ruhr Reservoirs Association (Maniak & Renz, 1978) . This means that in the Ruhr system the reservoirs are required only during periods of low flow. This reduces the necessary storage capacity. The supply district of the water works along the river is not restricted to the drainage basin of the Ruhr. It includes adjacent areas (Fig.l) (i.e. the drainage basins of the rivers Emscher, Lippe, and Wupper). Ruhr water which is pumped for domestic and industrial supplies in these adjacent areas or lost by evaporation from the supply system in the drainage basin of the Ruhr is termed "water losses" in this text. These water losses of 320 to 420 m3xl06year_1 or about 30% of minimum annual runoff are the crucial point for the formulation of the goals of water management in the Ruhr basin.
THE DUTIES OF THE RUHR RESERVOIRS ASSOCIATION
The water works along the Ruhr require a minimal water quantity and quality in the river. The water quality of the River Ruhr and its
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/rT Wate r pumped to adjacent areas ESSEN, DORTMUND = towns Rhine.Ruhr, Lenne.Volme = rivers FIG.l Water management system in the Ruhr drainage basin, 640 F.W.Renz tributaries is guaranteed by the Ruhr River Association (Ruhrverband, founded 1913) and the water quantity by the Ruhr Reservoirs Association (Ruhrtalsperrenverein, founded 1899). The organization and the financing of these two associations, operating in the natural drainage basin of River Ruhr, were formulated by two special laws of 1913 (RTG 1913, Imhoff, 1977). In the adjacent drainage basins other authorities were founded in order to resolve special water management problems (Imhoff, 1974; Londong, 1978). The special law for the Ruhr Reservoirs Association ("Ruhrtalsper- rengesetz") guarantees that the existing ecological system will not be changed by water abstractions for population and industry. The law requires an augmentation of low flows smaller than 4.5 1 s— 1k m 2 during dry periods by water from reservoirs of the association (Bower et al., 1981). Today a total storage capacity of 471.1 m x 10 exists from which only an effective storage capacity of about 410 m x 10 (cf. Table 1) can be used for replenishing natural runoff, i.e. a storage capacity nearly corresponding to the average annual amount of water
TABLE 1 Data from the large reservoirs in the Ruhr drainage basin
Moehne Henne Sorpe Bigge Verse Total
Gross storage capacity (m3 x 106 ) 134.134.5 .5 38. .4 70. .0 171. .7 32. .8 447. .4 Dead storage capacity (mi x 10°) 6. .7 2. .0 3. 5 7. .5 2. .0 21 .7 Net storage capacity (m x 10 ) 127. .8 36. .4 66. .5 164. .2 30. .8 425. .7 Drinking water (m3 x 10s) - - 0. .5 4. .0 12. . 3 16. .8 Effective storage capacity (m3 x 106 ) 127. .8 36. .4 66. .0 160. .2 18. .5 408 .9 Mean annual inflow (m3 x 10e) 204. .49 54. .87 45. . 33 225. .25 22. .04 551 .98 Percentage of the effective storage capacity of the system (%) 31.3 8.9 16.1 39.2 4.5 100.0
*Directly taken from the reservoirs by pipelines to supply adjoining towns and villages.
losses as defined above. But the water losses in drought periods can be completely replaced by the effective storage and the inflow to the reservoirs. Besides, it is necessary to maintain a fixed minimum runoff in the river at critical cross sections in order to preserve a given water quality. This statement applies to all droughts observed to date. During dry months in 1976 the efficiency of the reservoir system could be shown in practice by applying the operational plan, developed some years previously (Maniak & Renz, Management of the Ruhr reservoir system 641
1978). The deficits, which must be compensated by the reservoirs, can be calculated by the quantity of the water losses and the runoff at the mouth of the Ruhr taking into consideration the discharge and the natural inflow into the reservoirs.
DAILY WATER MANAGEMENT OF THE RESERVOIR SYSTEM
The data on actual storage, discharge, precipitation, and air temperature of the large reservoirs as well as information about the runoff at some critical cross sections of some rivers in the Ruhr basin are reported daily to the main office of the Ruhr Reservoirs Association in Essen. Supplementary information about the runoff at five important cross sections are telemetered to the main office. The actual storage volume in the smaller reservoirs and their discharges are reported on a weekly basis. In addition the ten largest water works and some other enterprises submit monthly reports on the amount of water taken out of the river system. These values are compared to the respective data of the last years. On the basis of these data the actual water losses are predicted. As a control the exact values of abstraction and water losses in the river system are annually inquired from all the water works, industrial enter prises, and other institutions using more than 30 000 m water per year. These data are evaluated for the individual parts of the river system. During critical low flow periods information about runoff, rain fall and air temperature and the results of a mathematical model are used as a basis for daily deciding the discharge of the reservoirs.
AVAILABILITY OF THE RESERVOIRS
Most men know by their own experience, that a car (especially their own) is not always available. Also a multireservoir system, such as the system in the Ruhr basin, cannot be considered as fully available all the time. One of the goals of water management is to arrange all necessary repair work in such a way that there is no, or only a minimal effect, on the availability of the system. But in fact there are many periods when the system is not fully available. Figure 2 shows the time periods, in which the total storage volume of the reservoirs was not fully disposable in the period from 1951 to 1978. All periods for necessary repair work on the dams as well as for other construction work by other authorities within or outside the reservoir, were included in as far as these construction works resulted in a reduction of disposable reservoir storage volume. The results are presented as a duration curve in Fig.2. It is to be seen that between 1951 and 1978 the reservoir system was not fully available for a total of 155 months which is 46% of 3 this period; in other words, a storage capacity of at least 10 m x 106 was lacking during this time. On the other hand, a shortage of 70 m3 x 106 was registered for 24 months, which represents 7% of the total period, or 17% of the effective storage of the reservoir system. On average there was a shortfall of about 28 m x 10 (Renz 642 F.W.Renz
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L,i LL| «4 ^ , | , rti duration [monthsj percentage of total time • 10 20 30 40 50 FIG.2 Duration curve of the non-available storage capacity of the Ruhr reservoir system. et al. , 1982). Similar reductions in the availability of the reservoir system have to be expected in the future, and could even increase in view of the considerable age of some of the reservoirs. Hence it follows that the mathematical model, based on the assumption of permanent full availability of the system, gives unrealistically advantageous results since in practice the effective disposable storage capacity is often not fully available.
OPTIMIZATION OF THE SYSTEM
Using the data of the historical time series from 1927 for the runoff at the mouth of the Ruhr and from 1935 for the inflow to all large reservoirs, the limit of the capacity of the system for several discharge requirements and/or replenishment of the water losses out of the Ruhr basin as well as an optimal operation of the total system and of each large reservoir have been determined by optimization of a mathematical model (Maniak & Renz , 1978). An optimal operating policy has therefore been developed; one part is applied in periods with normal rainfall and runoff, the other to critical dry periods in which maximum water losses have to be compensated by low-flow augmentation. According to these schedules, further conditions had to be imposed on some of the large reservoirs, e.g. fixed release regulations dependent on the runoff in a downstream river section or release obligations for direct drinking-water supply to the area around the reservoir. In addition, flood-control Management of the Ruhr reservoir system 643 storages which differ from month to month had to be provided in winter,
DATA FOR WATER f4ANAGEMENT AND PROBLEMS OF FORECAST
When the fundamental conception of the now existing water management system was determined more than 80 years ago, runoff data and data on the expected water demand of the region (based on estimations of the development of population and industry) were needed. Later permanent control and adjustment of the data were necessary. Today it is possible to compare some estimated data used for planning in the 80 year period with the subsequent measured values. First a comparison of runoff data for different time periods: Based on data of the period 1891-1915 a runoff depth at the mouth of the River Ruhr of 622 mm year_i was estimated. For the period 1927-1980 a runoff depth of 546 mm year- was later measured. This means that the forecast runoff was about 12% too high. The most important data for water requirements are the quantities of water pumped out of the River Ruhr into adjacent areas which is not returned to the river, the so-called water losses. In 1904 the quantity taken out of the River Ruhr and pumped into the adjacent basin of the River Emscher was estimated to be 136 m xlO year" , based on data from a water survey in 1897. On the basis of these data, it was calculated that 50 years later this value would be doubled, that is, 272 m x 10Jyear~ would be pumped out of the Ruhr drainage basin. A comparison with the data for 1954 shows that this figure was correct; therefore this first long-term fore cast proved correct. But this cannot be said of later forecasts for water demand, which were made always in order to estimate the necessary improvement of the reservoir system for the immediate or long-term future. Some examples of the evaluated data and the corresponding measured data are given in Table 2. It can be seen that the results of these forecasts are more often too high than too low and that for forecasts more than 15-30 years ahead these are extremely large errors. Today we have reliable forecasts of population and economic development only for about 10-15 years in the future. This means that the same time period is the expected upper limit for reliable water supply data. The water demand for public water supply in the future does not only depend on population development, but also on the expected size of each household, its standard of living, and the expected cost of water in the future. For these details we need also a reliable prediction. The industrial water demand is dependent on methods, quantity and cost of production and on the quality and cost of the needed water. Each change in industrial development results in a changed industrial water demand. But in the Ruhr district many changes in the industrial structure will take place. The development of water abstraction and losses in the last decades is shown in Fig.3. In the earlier decades there is a close relationship between industrial production (e.g. iron production) under constant economical conditions and water losses. But in the 644 F.W.Renz
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On the other hand, the time needed for the introduction of a new reservoir within our catchment area, including administrative approval, legislation and construction time is about 15 years (only 50% of this time is needed for construction). This means that 1900 1910 1920 1930 1940 1950 1960 1970 1980 FIG.3 Development of water abstraction and water losses as well as of iron production and population (1900-1980) in the Ruhr drainage basin. reliable forecasts for water demand are only possible for a time period which is just as long or even shorter than the installation time for the next necessary reservoir in the system. This is why a reliable optimization of the storage volume e.g. needed in the year 2010, is not yet possible. Only a trend with a wide range can be estimated. This range does not depend on the used mathematical (statistical) methods but on the kind of socio economic assumptions. EFFICIENCY OF THE RESERVOIR SYSTEM The gross efficiency rating of the reservoir system, that means what 646 F.W.Renz reservoir capacity is necessary to fulfil all the requirements deriving from water demand, is of extraordinary importance for determining the necessary capacity of the system. This factor is the actual reservoir discharge divided by the calculated necessary demand for low-flow augmentation. The gross efficiency rating can be calculated only subsequently and because of the system's slowness only for time periods of months or years. For the reservoir system in the Ruhr drainage basin the factor ranges in dry periods between 1.2 and 1.3. In the mathemat ical model a factor of 1.23 was used. Other reservoir systems show similar efficiency factors, e.g. the Eder dam, also situated in the FRG and used for augmentation of the upper part of River Weser to make it suitable for shipping, has an efficiency of 15-30%. The more frequent the change between times of necessary augmentation and times without augmentation the higher the factor. In the Ruhr reservoir system the factor of gross efficiency rating is mainly dependent on: (a) The hydrological situation within the time period (length of dry periods, frequency, depth, intensity and distribution of rainfall, especially thunderstorms etc.). (b) The relation between the reservoir storage volume (m xlO") usable for discharges and the demand for low-flow augmentation (m xlO ). (Each new reservoir in the system as well as each increase or decrease for water demand changes this relationship.) (c) The maximum possible accuracy for estimating the necessary augmentation over the next few days; this is based on previous data from the water works and on more or less reliable weather forecast , especially concerning the expected rainfall depth and its distribution. (d) The maximum possible accuracy of runoff determination at the different control sections in the system (even during extremely and rarely observed low-flow situations or when the telemetric systems are interrupted or when the recording is disturbed by vandalism). (e) The amount of losses due to evaporation and infiltration between the reservoirs and abstraction points situated more than 100 km downstream as well as the possible accuracy of the estimation of these losses for the next few days. The losses due to evaporation are the greater the larger the evaporation areas. These areas have considerably increased in size in the last few decades, in some cases they have more than doubled (e.g. impounded lakes working as purification lakes and besides used as recreational centres, basins for artificial groundwater recharge by the water works). To estimate the most unfavourable evaporation losses, values for critical drought periods should be used. Evaporation losses of the surface of lakes and rivers between the inflow gauges of the reservoirs and the abstraction points of the most downstream situated water works were estimated for the hydrological summer half-year (1 May to 31 October) on the basis of values measured during the summer of 1976. On average the evaporation losses were between 12.7% and 19.1% of the total "water losses" in the Ruhr drainage basin. On extremely hot days, the losses due to evaporation can reach up to 10 mm day-1, this means 0.427 m3xl0 day-1 or 4.94 m s-1, that are between 21.7% and 49.4% of the total water losses of the Ruhr drainage basin. Management of the Ruhr reservoir system 647 CONCLUSIONS A multireservoir system like the Ruhr basin system cannot be considered as fully available all the time. All periods of time in which parts of the system were not fully disposable and the corresponding storage capacity are collected and presented as a duration curve. It would be helpful to have similar data from other systems but there are no references to this topic. Such a reservoir system has also a gross efficiency rating with respect to the goals of water management. The main components of these efficiency factors are described. In dry periods the real discharge of the reservoir system is 20-30% higher than the calcul ated losses, which have to be substituted. There is great interest in the efficiency factors of other reservoir systems. Such a knowledge would be helpful by calculating the effective capacity of new systems. Moreover information about natural flow and water demand data are given. A comparison between predicted and measured data for water demand shows differences, which are the greater the longer ahead the forecast. In the Federal Republic of Germany the period of time for which reliable forecasts are possible is today as long or as short as the time needed for planning, controlling, approval and construction of a new reservoir. This means that the optimization of the reservoir system for the decades of its usage time, even based on the newest mathematical methods, is not very helpful as there is no reliable data base. REFERENCES Bower, Barré, B.T. Kuhner, R.J. & Russel , C.S. (1981) Incentives in water quality management: France and the Ruhr area. Resources for the Future, Research Paper R-24 , Washington, DC. Imhoff, K.R. (1974) Water quantity and quality management in the Ruhr Valley. J. Wat. Pollut. Control Fed. 46 (7), 1663-1673. Imhoff, K.R. (1977) Bewirtschaftung und weiterer Ausbau der Ruhrtalsperren. Wasserwirtschaft 67 (7/8), 229-236. Imhoff, K.R. & Mantwill, H. (1980) The recreational uses of reservoirs and impounded lakes in the Ruhr catchment. Progr. Wat. Tech. 13, 127-138. Londong, D. (1978) Water quantity management in the West German canals and Lippe River. (IAWPR Specialized Conference on River Basin Management, Essen 1977) Progr. Wat. Tech. 10 (3/4) 267-275. Maniak, U. & Renz, F.W. (1978) Optimal operation of the system of Ruhr Reservoirs. (IAWPR Specialized Conference on River Basin Management, Essen 1977) Progr. Wat. Tech. 10 301-311. Renz, F.W. (1980) 75 Jahre Talsperrenbewirtschaftung im Einzugsgebiet der Ruhr. Wasserwirtschaft 70 (1), 2-4. Renz, F.W., Plewa, R., Maniak, U. & Seeger, D. (1982) Bewirtschaftung der Talsperren im Einzugsgebiet der Ruhr. Eigenverlag des Ruhrtalsperrenvereins Essen, Essen. RTG (1913) Ruhrtalsperrengesetz vom 5. Juni 1913. PR GS. 1913, S. 317, Berlin.