Floods are the most frequent natural hazard worldwide - in Europe, river flooding is particularly common. Floodplain forests can help. These biodiversity hotspots protect against flood damage.
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00:00Rivers aren't supposed to look like this. Today, many of them are straight, narrow, deep, depleted and surrounded by concrete.
00:07That's because humans have a long history of changing rivers and their landscapes so they can use them for farming, industry, transportation and to build houses close to the edge.
00:19This river here is a great example of how we have messed with our landscapes. As you can see, it's been straightened, regulated and diked.
00:25Also, parts of its floodplains on its side, which would usually provide space for overflowing water, have been drained and filled.
00:32The rivers and floodplains in this area serve an important function, though.
00:36They cross the cities of Leipzig, Makleberg and Skoites and are supposed to store and supply water to one of the largest urban floodplain forests in Central Europe that is home to many animals and plant species.
00:47But from the middle of the 19th century, dams and bridges for railroads were built here, right through the forest.
00:53And during that process, former river courses in this area were cut off and are now lying dry.
00:57And all this means they can no longer supply water to the floodplain forest.
01:01And that's not just happening here.
01:03Around two-thirds of the floodplains along Germany's 79 major rivers can no longer serve their original purpose of storing excess water because of the dikes built to stop water from reaching them.
01:13One-third of the remaining floodplain areas are covered by fields and houses.
01:18And it's happening across Europe, where 70 to 90 percent of floodplains have been environmentally degraded.
01:23Asia and the Americas are also struggling with depleted floodplains.
01:27So, why is that a problem?
01:29Floodplains are not only important ecosystems.
01:32They also absorb and store carbon from the atmosphere, helping tackle climate change.
01:36And, maybe most importantly for the people who live along the rivers, they keep flash floods in check.
01:42Functioning floodplain forests are very important because they keep water in the landscape longer.
01:47They soak up water and provide the crucial sponge function.
01:52That's Matthias Scholz, a floodplain ecologist.
01:55He's been studying the role of rivers and coastal wetlands for decades.
02:01Without floodplains and floodplain forests, water flows out of the landscape very quickly,
02:05leading to large flood waves that cause a lot of damage, and the cost is enormously high for society.
02:14That's why Scholz, together with the cities of Leipzig and Schneiditz,
02:17the University of Leipzig and the environmental association NABU,
02:20decided to give the floodplain landscape here a more natural face again.
02:25Forty years ago, we realized this floodplain forest was undergoing a process of expansion.
02:30Many trees developed here that were not flood-resistant
02:33and which displaced the tree species typical of a floodplain forest.
02:40Oak trees like this one and elm trees like this one started to die off,
02:44while other species that are a lot less resilient to flooding, like maple, started to spread.
02:51When the floodplain dries out, along come the maple trees. Here's a good example.
02:57They have a white, milky sap. The other species find it difficult to compete with them.
03:04And those other species protect us against flooding?
03:09Exactly, because those species are highly resistant to flooding.
03:17That's because those species can handle being flooded better than others.
03:20They can also handle droughts better.
03:22And they suck moisture out of the soil, which decreases the amount of water contributing to flesh flooding events.
03:28So, the researchers had an idea.
03:30They started purposefully flooding a small area of the forest every spring for decades and watched what happened.
03:39We found out that that allowed the forest to stay moist for up to three months longer, even during drought periods.
03:46And that this floodplain forest was able to adapt to these wetter, more dynamic conditions.
03:52So, species that don't belong here receded,
03:55leaving space and light for the tree, animal and plant species that are typical of the floodplain forest.
04:05They literally trained the forest to be able to soak up more water again.
04:11Even with flood-resistant trees, if they don't experience flooding for a long time,
04:15they may forget how to cope with it or how to adapt to it.
04:20Scholz says the data they collected over 30 years tells the story of an ecosystem going back to its natural state.
04:28This is a 3D model of a 7-hectare forest area that they flooded and surveyed for three decades.
04:33Just look at how many red trees there were before they started flooding the area.
04:37Those are untypical, sometimes invasive species that are not so resilient to floods and drought.
04:42And now look how many green trees came back once they started flooding the area.
04:46Those are typical native floodplain trees, which are resistant to floods and droughts.
04:51Here you can clearly see that the maple is dying.
04:54This area has been underwater for several weeks.
04:57And right next to it is the flood-tolerant European ash, which looks very healthy.
05:05They were surprised by how fast the forest went back to its natural state once they started adjusting the water levels.
05:11For us, these are nature-based solutions, which will help mitigate the extreme events we expect from climate change.
05:21So how exactly did they flood the area?
05:25At the end of the 1990s, the city of Leipzig began reconnecting old channel systems in the floodplain,
05:32like this one here, the Burg Auenbach, to the main watercourses, so that the forest could access water again.
05:41We reconnected the old historical channel systems that were still in place.
05:47This ditch was partly restored by hand.
05:53The channel systems were connected, and then an intake structure was built in the dike,
05:58which fed water back into the channel systems.
06:02They then cut out several parts of the dike on the riverside, so that the water can naturally overflow into the floodplain.
06:12We're seeing a clear and measurable rise in groundwater levels, even within a very short space of time.
06:18And even with such a small water body, there are visible, measurable results.
06:24Back then, it was easy to get a permit for an undertaking like that.
06:28Today it's far more complicated. There are new guidelines, EU regulations, which have to be followed.
06:34More evidence is needed, more calculations. It's not as simple as it used to be.
06:40But that didn't stop the city from doing more.
06:42It brought together scientists, NGOs and local officials in 2018
06:46to come up with a concept to rejuvenate the entire floodplain over the next 30 years.
06:51And they just finished their first project.
06:53They restored this historic riverbed here and designed it in a way where it can overflow more naturally, regularly and predictably,
06:59like it did in the past, before we altered rivers.
07:03As you can see here, we've moved the field relatively far away from the edge of the forest,
07:08creating a large corridor in which the water can meander freely.
07:14That's Christiane Frohberg, who was responsible for revitalizing this old riverbed.
07:18We have several outlets through which, when the flood comes, the rising water can flow.
07:24It flows over this very low bank directly into the forest.
07:29This means that with the 5.5 kilometers of new waterway, which we've recently finished building,
07:34we can flood around 45 hectares of floodplain forest several times a year.
07:42That's roughly the size of 84 football fields.
07:44And that's also good news for the animals who live here.
07:46Fish and rare species of insects have already settled in.
07:49But it wasn't easy to get to this point.
07:51It's a tricky process to find a balance between flooding the forest enough
07:55so it re-learns how to suck up more water and not over-flooding it,
07:58otherwise the water could permanently stay there like in a bathtub,
08:01which would change the entire ecosystem.
08:03And you have to consider different interests.
08:06We're in a big city, so there are many different views on how the environment should be.
08:11And recreational use is particularly important.
08:14That means that if we flood certain areas and some paths become inaccessible in spring as a result,
08:20we need to explain this and provide information or offer alternatives.
08:25Though actually we found that there is a very high level of acceptance
08:29and that people often find very creative solutions.
08:33I'm so happy right now.
08:36Because it really was years of talking to people every day,
08:39making sure that they weren't afraid of the water coming in.
08:43And it's just wonderful to see that we now have water in this small river.
08:47Despite its size, it has a big impact.
08:51And it's just wonderful to see that we now have water in this small river.
08:54Despite its size, it has a big impact.
08:57It's not just people using the forest for recreational purposes
09:00who needed to be convinced about the flooding plans.
09:02Local farmers had to be on board as well.
09:05You can't expropriate people without offering alternatives.
09:08Bringing more water into the landscape doesn't mean giving up agricultural use.
09:12You just have to adapt the agricultural practices.
09:15Like turning once arable land into a wild meadow.
09:18And then of course you have to make sure that there is enough water.
09:21That means, instead of planting corn and rapeseed on all of their land,
09:24farmers would plant grass in some areas and sell the hay instead.
09:27They would also receive a compensation payment, Scholz says.
09:31The goal for the next 10 to 15 years is to revitalize
09:34more than 16 kilometers of former arms along the river.
09:37They want to reconnect dried-up river arms
09:39and inundate at least 30% of the floodplain area via the river.
09:42And that's what they're doing right now.
09:44The goal for the next 10 to 15 years is to revitalize
09:47more than 16 kilometers of former arms along the river.
09:50And that's what they're doing right now.
09:52So that instead of this, the area will look like this.
09:57And here they already started turning former farmland into a floodplain forest.
10:01They planted species resilient to flooding
10:04so that future floodwaters can be sucked up by the plants like a sponge.
10:07That way, Scholz says, they can also get more water to stay in the ground.
10:12Of course, projects like this come with a hefty price tag.
10:15The city of Leipzig already spent 6.5 million euros,
10:18largely funded by the German state,
10:20to buy back land and build new bridges and gateways
10:22for crossing the newly restored river.
10:27It will require a great deal of effort
10:29to get this project approved here in the region and by the authorities
10:33so that the further steps can be taken to preserve the floodplain forest
10:37and so that funding in the tens of millions can be put in place.
10:43It sounds like a lot,
10:44but flooding is actually the most expensive natural hazard in Europe.
10:47With one study estimating that river-based flood risk
10:50could increase sevenfold to 6.8 billion euros by the end of the century.
10:54Most large European cities are situated on floodplains.
10:57These are the ones that are predicted to suffer a lot of flood damage in the future.
11:03And the changes we've made to most of our waterways
11:05are adding to the flood risk, not detracting from it.
11:10That's why EU environmental ministers recently approved
11:13a contested nature restoration law
11:15that seeks to regrow forests, re-wet peatland
11:17and return rivers to their natural, free-flowing states.
11:20A move that Scholz welcomes.
11:26When we consider the monetary damage that extreme events can cause to our society
11:31and the long-term effects required to address them,
11:34it's clear that putting money into ecosystem restoration
11:37is a future-proof investment.
11:40That's why more and more European cities situated on floodplains
11:43are experimenting with nature-based approaches like this.
11:46And the project here in Leipzig has become a blueprint for others.
11:49Scholz has been cooperating with colleagues from Estonia, Spain and Portugal
11:53to share knowledge and best practices,
11:55such as how to retain water in an area as long as possible.
11:59And there's a lot that other countries can learn from their success.
12:02More than anything, it's important to get the landowners and tenants,
12:06the farmers and the foresters on board,
12:08and to make decisions together with them on site
12:11and not just with planners at the drawing board.
12:16When nature functions properly, it works for us
12:19and we can benefit from all that it offers us.
12:22And that's an insurance policy for the future.