All things environmental

Musings about the environment and all it touches, from education to city planning

The Isebek, or how to bring a canal back to life

leave a comment »

A view of the Isebek canal in Hamburg

A view of the Isebek canal in Hamburg

The Isebek is the most urban of all the canals that flow into Alster Lake in Hamburg. It is also the most polluted – or at least it used to be. How it came back to life is a remarkable story, and one that has lessons for Vancouver.

The Isebek canal, west of Alster lake

The Isebek canal, west of Alster lake

A bit of historical context is needed here. The Isebek river gets its name from a dialect form of Eisen, or iron; this already indicates potential problems. The river was channeled into a canal in the nineteenth century, to facilitate transport, at about the same time as sewers were being built. (This was done after 1842, when the city rebuild after a catastrophic fire that destroyed most of the city.). Before then, waste flowed directly from gutters into the creek, or was dumped from buckets, causing citizens to complain about the stench in summer. The sewers helped, but there was no treatment: both rainwater and wastes were conveyed through these pipes, what we now called combined sewers. But the lack of treatment meant that, even with the smaller population of the 1800s, the creeks and canals were badly impacted; since many had to get their drinking water straight from there, it is no surprise that Hamburg suffered a massive cholera epidemic in 1892.

The city responded – grudgingly, and too late – by providing a network of piped water, and eventually channeling all the sewers into large pipes that deliver sewage to treatment plants along the Elbe. This helped clean up the creeks and canals, and fish came back.

This should have been sufficient for canals like the Isebek, except for one thing: the older sewers are still combined sewers. This means that they overflow during storms, straight into the canals. This is particularly acute along the Isebek, since the area is densely built-up and there are few natural areas that allow rainfall to gently seep into the ground. (A similar issue exists in Vancouver and New Westminster, by the way: sewers in both areas are combined, and overflow into the Fraser or Burrard Inlet at every major storm.) As a result, though fish were now back living in the Isebek, fish kills following storms were frequent until the 1990s.

The Isebek runs through tony Eimsbuttel - right behind these buildings

The Isebek runs through tony Eimsbuttel – right behind these buildings

In the 60’s the city thought that the easiest way to deal with the problem was to make it go away: pave the damn thing. This was narrowly avoided through extensive public protests. So Hamburg – grudgingly, again – launched a series of initiatives, and then got caught at its own game, deciding to get serious and push for the Greenest City Award, which it got in 2011.

First, the city built a series of underground storage basins to collect storm runoff and prevent overflow of the combined sewers into the canals. The storage basin for the Isebek, on Lehmweg, has 7,500 m3 of capacity and helps prevent overflows from six combined sewers outfalls. Curiously, the structure is often used as a meeting point for walking groups.

The sewage reservoir on the Isebek

The sewage reservoir on the Isebek

(This is something that I’d like to see Vancouver do. Yes, these are big, costly projects. But they create jobs, and mostly, they really help, and our salmon could use a hand.)

That alone isn’t quite enough. Combined sewer overflows have been reduced by 70%, which is great. But Hamburg is looking at the writing on the wall: climate change. Worse storms are coming.

So the city has decided to embark on a series of new initiatives. One is the completion of a mega interceptor to channel sewage away from the combined sewers. This is a huge project, and my first inkling of it was a chance meeting with a legal photographer: someone who takes pictures of all the buildings, heritage and otherwise, before work proceeds, so that if someone sues the city for cracks or damages, there is documentation.

Another measure that has been used on the Isebek is aeration. The canal is quite shallow (less than one meter in places) and the water is often stagnant. So the canal would stink in summer, even without overflows. To prevent that, the city installed an aeration tube that runs the length of the canal, diffusing air into the canal water like some giant aquarium. The system, two kilometers worth of pipe with 6000 diffusers, has been in operation since 1990.

Despite the urban setting, the Isebek has some wooded shorelines

Despite the urban setting, the Isebek has some wooded shorelines

But another key initiative is the one called the Green Network. Ostensibly intended to create green spaces, one of the main objectives of the initiative is stormwater management. By increasing surfaces where rain water can infiltrate – green roofs, rain gardens, porous pavings, etc – the city hopes to prevent the worse of local storm flooding. As a result, storm sewers have less water to deal with, and are less likely to overflow.

Does that mean that the water is now fine and safe? By and large, yes, but not completely. A few years ago, a 44 year old man came down with a mysterious illness characterised by a high fever. This was a rare case of leptospirosis, and he most likely contracted the bug while practicing eskimo rolls in his kayak on the Isebek. Leptospirosis is caused by a nasty bacterium carried by mice and rats, and is not a reflection of poor water quality; but still.

I would so love to see my city copy some of these initiatives. Vancouver has embarked on a 100 year-long program of replacing combined sewers with separate sanitary sewers and storm drains. It is hugely costly, and of questionable effectiveness, since storm water itself can be fairly contaminated. (In separate sewers storm waters are not treated.) Instead, how about a few storage basins, a clever system of outflow control, and especially, especially, green infrastructure: rain gardens, green roofs, infiltration basins…it’s not like we lack the space, being built much less densely than Hamburg. Yet, dense as it is, Hamburg is finding a way to go green.

A little pontoon house nestled among the buildings

A little pontoon house nestled among the buildings

Why is that so? I don’t know, but here’s a hint. The environmental group NABU mounted a campaign, a few years ago, against a project approved by the city. This was to be an office complex near the Isebek; NABU said it was in the wrong place, would damage some critical bird and bat habitat, and mostly the paving of the site would send a lot of excess surface runoff to the beleaguered Isebek. Faced with ongoing public opposition, the city relented and withdrew its approval. They listened to their citizens.

I guess they have to: like its federal counterpart, the political system here has been mixed proportional since the end of the war. That means government by coalition, where being attuned to the public is key to staying in power.


Written by enviropaul

November 10, 2015 at 12:19 pm

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: