Preface by Katharina Dujesiefken

BUND MECKLENBURG-VORPOMMERN Preservation and planting of trees on dams and dykes Conflicts - Solutions - Implementation PHOTO Common oak avenue at the Störkanal 2016 (Ralf Ottmann). Content | 5 Content 6 Preface 8 Different assessment of the effect of woody plants on dams and dykes 8 Legal significance of standards 10 What is a dam, what is a dyke? DEAR READERS, 11 Rehabilitation of dams with preservation of the tree population using the example of a Stör waterway When I first saw the oaks along the (Articles by Katharina Dujesiefken and Frank Chris- Stör-Canal, I was deeply impressed toph Hagen) by the beauty and grandeur of these sturdy trees. They have been stan- 12 History of the Stör waterway ding on the dam along the Canal for about 140 years. They always had 14 Dam reconstruction on the Stör waterway good growing conditions, enough (StW) - the planning approval decision 2013 space for the roots and enough water. No de-icing salt in winter, few 28 Reconstruction of dykes with preservation of the cuts, no root digging. The trees could tree population using the example of the Rhine simply develop wonderfully and so dyke in Neuss (Article by Dr. Ing. Lothar Wessolly) they stood there, one as beautiful as the other. But now they should 34 Animals at the dyke be felled with the renovation of the dams. It was immediately clear to 37 Instructions for planting on dams and dykes me that BUND, together with many allies, would have to find a solution 38 Literature that would make it possible to pre- serve this old Canal avenue. In this brochure we show how joint com- mitment can lead to a good result. Katharina Dujesiefken Consultant for tree and avenue protection 6 | Preface Preface by Katharina Dujesiefken The development of human ci- pened. Transport is therefore cannot be avoided. vilization is connected with the faster, without obstacles and is desire for more land, navigabili- possible for larger ships. This In the last 250 years, many ty and flood protection. Rivers encouraged trade. Cities and near-natural habitats such as and streams were straightened industry developed along the floodplain forests with their and dyked. A large number of rivers. It was promised that winding arms of water have once meandering rivers and the straightening of the rivers disappeared and made way for streams now run through the would prevent flooding, but the open, bare agricultural land. landscape as strictly uniform floods have only shifted downs- Straightening and contain- structures. They were once tream. When, for example, the ment led to a decline in the wider and shallower and spread Upper Rhine was straightened biodiversity of animals and over an entire river plain. at the beginning of the 19th plants. In the course of river Floodplain forests grew on their century, there were warning straightening, accompanying banks. There was a great variety voices. They were right, becau- trees and shrubs were and are of animal species on land and se as a result the Middle and often removed. Due to the lack at sea. Lower Rhine rivers were over- of trees and shrubs, the effect flowing their banks like never of light on the river becomes Today, these waterways are before. As long as the rivers much stronger, which promotes shortened, straightened, dee- do not get more space, floods the growth of aquatic plants. PHOTO Common oak avenue at the Störkanal 2016 (Ralf Ottmann) Preface | 7 „In the last 250 years, many near-natural habitats such as floodplain forests with their winding arms of water have disappeared and made way for open, bare agricultural land. Straightening and containment led to a decline in the biodiversity of animals and plants. In the course of river straightening, accompanying trees and shrubs were and are often removed.“ This effect is supported by the Engineering biology has very dam rehabilitation with preser- stronger warming of the water. good answers to the question vation of the tree population Heating the water also results of how plants can be used as is possible and even sensible. in a decrease in oxygen, as the living building materials to In both cases, it was only after warm water can absorb less secure dams and dykes. For extensive protests that trees and less oxygen. In addition, many decades, representatives were preserved and the neces- the lack of vegetation on the of nature conservation and sary work on the dams had to dams and dykes means that dirt landscape management, asso- be discussed with a tree expert. and fertiliser cannot be retai- ciations and local citizens have In this publication we show the ned. Of course, with the trees been calling for environmental- results of the planning, prob- and shrubs along the water, ly compatible solutions to be lems and solutions during the important habitats are missing implemented. implementation. for many animal species. In addition, the Canalised rivers This brochure uses the example and streams lack the organisms of the rehabilitation of the Stör in the waters and the time for waterway in the Lewitz with an sufficient self-cleaning. oak avenue and the preservation of a horse chestnut avenue For these reasons, landscape on a Rhine dyke to show that architects, engineers, biologists and many a hydraulic engineer are questioning the demand currently manifested in standards, which states that woody plants (trees, shrubs and hedges) on dykes and dams are fundamentally unacceptable because they apparently impair stability and maintenance (DIN 19712, Merkblatt Standsicher- heit von Dämmen an Bundes- wasserstraßen, 2011). Those responsible refer to this not only for new construction, but also when it comes to tolera- ting and planting trees on dams and dykes during renovation measures. Norman Voigt Norman PHOTO PHOTO 8 | Different assessment of the effect of trees and shrubs on dams and dykes Different assessment of the effect of trees and shrubs on dams and dykes DIN 19712 - Flood protection ted from the wind or whether they (BAW) “Merkblatt Standsicherheit works on rivers (2013) states are exposed to the storm, whether von Dämmen an Bundeswasser- in paragraph 7.5.5 „Woods and there is a strong current or a calm straßen, 2011” (Stability of dams shrubs (trees, bushes and hedges) lake. Trees are unpredictable for on federal waterways; edition on dykes impair stability and main- hydraulic engineers. They can fall 2011) also states that no wood tenance and are therefore gene- over and tear holes in the dyke. growth on dams should be per- rally not permitted“. They would It is often more important to take mitted. According to this, woody impair stability and maintenance. this into account than to include plants (trees and shrubs) pose a the reinforcing effect of tensile danger to stability. This is justified If trees and shrubs are required structures, the roots (WESSOLLY, as follows: on dykes in exceptional cases, this L. 2019). would normally only be possible • Wind induced movements of with an oversized dyke cross-sec- Each standard can only provide the tree lead to loosening of tion (over-profile) or if special se- orientation, but must be expert- the soil. curing elements (e.g. sheet piling) ly supplemented or updated on are installed. site. Therefore, it is important • Throwing wind from trees can to question the background and lead to a considerable weake- Although the DIN standards are the scientific resilience of a DIN ning of the dam cross-section. not binding, they are often hand- standard. It is also important to led like laws by the responsible determine whether the rough ge- • Dead roots of old woody authorities and implemented neralisation of the DIN standard is plants can lead to cavities in without compromise. In the case in line with the specific situation. the dyke. of DIN 19712, this applies not only to the construction of dams The introduction to the standard • The turf is suppressed by the and dykes, but also to renovation then also contains the sentence: constant shading. measures. However, the standard „The principles contained in this does not take local circumstances standard are to be adapted or • Woody plants favour the co- or situations into account. supplemented according to the lonisation of rooting animals, respective local conditions“. whose ducts, as well as the In practice, no consideration is roots of dead trees, are prefer- usually given to whether the trees The data sheet of the Federal red drainage paths. on the dykes or dams are protec- Waterway Research Institute • Dam observation, which requi- res complete visibility of the Legal significance of standards - Is a DIN standard binding? air-side embankment, can be considerably impaired by trees A DIN standard is a voluntary standard drawn up under the direction of and shrubs. a working committee at the German Institute for Standardization (DIN). DIN standards are based on the proven results of science, technology and • Mechanical maintenance of experience and serve the general public. DIN standards are recommendati- the dyke / dam is made more ons and can be applied, but they do not have to be used. In principle, these difficult. are „private standards of a recommendatory nature“. As such, they may lag behind the state of the technology, but have the claim that they reflect the state of the art. This claim can be challenged by expert evidence (https:// de.wikipedia.org/wiki/DIN-Norm). Different assessment of the effect of trees and shrubs on dams and dykes | 9 „Although the DIN standards are not binding, they are often handled like laws by the responsible authorities and implemented without compromise.“ On the other hand, Katzenbach (kubus - Technische Universität interactions and safety of horse and Werner describe an increase Berlin: Darstellung der Wurzelver- chestnut trees in an avenue on in the strength of rooted earth läufe und bodenkundliche Feldan- a Rhine dyke.

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