The area of the watershed of the Elbe above Altona is about 52,000 square miles, and the average rainfall is estimated to be about 28 inches, varying from 24 or less near its mouth to much higher quantities in the mountains far to the south. On this watershed there are 46 cities, which in 1890 had populations of over 20,000 each, and in addition there is a permanent population upon the river-boats estimated at 20,000, making in all 5,894,000 inhabitants, without including either country districts or the numberless cities with less than 20,000 inhabitants each. The sewage from about 1,700,000 of these people is purified before being discharged; and assuming that as many people living in cities smaller than 20,000 are connected with sewers as live in larger places without being so connected, the sewage of over four million people is discharged untreated into the Elbe and its tributaries.
The more important of these sources of pollution are the following:
| City | Population in 1890. | On what River. | Approximate Distance, Miles. |
|---|---|---|---|
| Shipping | 20,000 | —— | —— |
| Altona | 143,353 | Elbe | 6 |
| Hamburg | 570,534 | Elbe | 7 |
| Wandsbeck | 20,586 | Elbe | 8 |
| Harburg | 35,101 | Elbe | 11 |
| Magdeburg | 202,325 | Elbe | 185 |
| Dresden | 276,085 | Elbe | 354 |
| Berlin and suburbs | 1,787,859 | Havel | 243 |
| Halle | 101,401 | Saale | 272 |
| Leipzig | 355,485 | Elster | 305 |
| Chemnitz | 138,955 | Mulde | 340 |
| Prague | 310,483 | Moldau | 500 |
The sewage of Berlin and of most of its suburbs is treated before being discharged, and in addition the Havel flows through a series of lakes below the city, allowing better opportunities for natural purification than in the case of any of the other cities. Halle treats less than a tenth of its sewage. Magdeburg will treat its sewage in the course of a few years. Leipzig, Chemnitz, and other places are thinking more or less seriously of purification.
The number of bacteria in the raw water at Altona fluctuates with the tide and is extremely variable; numbers of 50,000 and 100,000 are not infrequent, but 10,000 to 40,000 is perhaps about the usual range.
The works were originally built by an English company in 1860, and have since been greatly extended. They were bought by the city some years ago. The water is pumped directly from the river to a settling-basin upon a hill 280 feet above the river. From this it flows by gravity through the filters to the slightly lower pure-water reservoir and to the city without further pumping. The filters are open, with nearly vertical masonry walls, as described in Kirkwood’s report. The cross-section of the main underdrain is 1⁄2800 of the area of the beds.
Considerable trouble has been experienced from frost. With continued cold weather it is extremely difficult to satisfactorily scrape the filters, and very irregular rates of filtration may result at such times. In the last few years, with systematic bacterial investigation, it has been found that greatly decreased efficiency frequently follows continued cold weather, and the mild epidemics of typhoid fever from which the city has long suffered have generally occurred after these times. Thus a light epidemic of typhoid in 1886 came in March, following a light epidemic in Hamburg. In 1887 a severe epidemic in February followed a severe epidemic in Hamburg in December and January. In 1888 a severe epidemic in March followed an epidemic in Hamburg lasting from November to January. Hamburg’s epidemic of 1889, coming in warm weather, September and October, was followed by only a very slight increase in Altona. In 1891 Altona suffered again in February from a severe epidemic, although very little typhoid had been in Hamburg. A less severe outbreak also came in February, 1892, and a still slighter one in February, 1893. In the ten years 1882-1892, of five well-marked epidemics, three broke out in February and two in March, while two smaller outbreaks came in December and January. No important outbreak has ever occurred in summer or in the fall months, when typhoid is usually most prevalent, thus showing clearly the bad effect of frost upon open filters (see Appendix II). With steadily increasing consumption the sedimentation-basin capacity of late years has become insufficient as well as the filtering area, and it is not unlikely that with better conditions a much better result could be obtained in winter even with open filters.[63]
The brilliant achievement of the Altona filters was in the summer of 1892, when they protected the city from the cholera which so ravaged Hamburg, although the raw water at Altona must have contained a vastly greater quantity of infectious matter than that which worked such havoc in Hamburg.
From these records it appears that for about nine months of the year the Altona filters protect the city from the impurities of the Elbe water, but that during cold weather, with continued mean temperatures below the freezing-point, such protection is not completely afforded, and bad effects have occasionally resulted. Notwithstanding the recent construction of open filters in Hamburg it appears to me that there must always be more or less danger from open filters in such a climate. Hamburg’s danger, however, will be much less than Altona’s on account of its better intake above the outlets of the sewers of Hamburg and Altona, which are the most important points of pollution at Altona.