Flood control by Plants

Dr. Khalid Rehman Hakeem

Fellow Researcher

Faculty of Forestry

Universiti Putra Malaysia (UPM)

Serdang-43400

Not so good pictures

Kelantan Flood 2014-15

Uttrakhand, India Flood 2013

Kashmir Flood 2014

SOFT ENGINEERING

HARD ENGINEERING

Trees can provide an effective eco- friendly method

of reducing the severity of flooding.

Trees are Nature's helpers in the task of

reducing geomorphological instability and

slow down erosion phenomena, and this

works for river basins too.

Can trees be used strategically to prevent flooding?

Absolutely

Most of the tree and shrub species that are typical of river banks and levees ("riparian vegetation") do absorb a lot of water (they are called hygrophylic species) and their roots strengthen the shores. In particular in ‘flash floods’ trees, and vegetation in general, can have a very important role: •They hold the shores and keep the river bed in place and in shape.

This helps the water flush away reducing the length of the flood. •They serve as a "filter" for floating objects (such as rocks, trees and debries), that are a major threat during floods because they crush on house and infrastructure or they create"lids"under bridges. When pressure builds up, these lids either crush creating a second flood wave or they tear the bridge down. •They slow down the water reducing flood energy and therefore, the threat for people and buildings.

Healthy forests and wetland systems provide a host of watershed services, including water purification, ground water and surface flow regulation, erosion control, and stream bank stabilization. The importance of these watershed services will only increase as water quality becomes a critical issue around the globe. Their financial value becomes particularly apparent when the costs of protecting an ecosystem for improved water quality are compared with investments in new or improved infrastructure, such as purification plants and flood control structures – in many cases it is often cheaper and more efficient to invest in ecosystem management and protection.

Forestry and watershed services

Can forestry reduce flooding?

Forest soils typically have a relatively open,

organic rich upper layer, which facilitates

the rapid entry and storage of rain water.

Forests are known to use more water than

shorter types of vegetation. This is mainly

due to the interception of rainwater by their

aerodynamically rougher canopies.

Interception can reduce the amount of

rainfall reaching the ground by as much as

45% or more for some types of forests. A

reduction of even half of this amount could

therefore make a major contribution to flood

control.

http://www.forestry.gov.uk/

1. Water use by trees

Trees and Forests can use more water than

shorter types of vegetation mainly due to the

interception of rainwater by their

aerodynamically rougher canopies (Nisbet, 2005).

Studies in the UK have found that between 25

and 45% of annual rainfall is typically lost by

interception from conifer stands, compared to 10-

25% for broadleaves (Calder et al., 2003).

Another factor is tree age, with the greater

water use of forests only becoming fully

established when the canopy closes, which tends

to occur at around 10-15 years age in conifer

plantations and even later for broadleaves.

2. The ‘sponge effect’

Forests can affect flood flows is by their soils holding back and delaying the passage of rain water to streams and rivers. Forest soils tend to have a more open structure resulting from greater amounts of organic matter, the action of tree roots and soil fauna, and the lower level of soil disturbance by man. The presence of a network of macropores helps to transmit water quickly to depth, reducing the likelihood of surface saturation and rapid run-off. These conditions enhance the ability of the soil to receive and store rain

water and are commonly referred to as a ‘sponge effect’. Journal Water Resources Research by scientists at the Smithsonian Tropical

Research Institute (STRI) and other institutions finds that forests in Panama help moderate extreme weather events by reducing peak runoff during storms and releasing stored water during droughts. The findings are based on measurements taken during nearly 450 tropical storms in forests and pastures.

“Storm-water runoff from grazed land is much higher than from forested land. The results are clearest after big storms.”

3. Hydraulic roughness

The use of riparian and floodplain forest to delay the progression of flood flows may offer the greatest potential to assist flood control. This relies on the hydraulic roughness created by woody debris dams within stream channels and by the physical presence of trees, shrubs and deadwood on the floodplain. The net effect of these features is to reduce flood velocities, enhance out of bank flows, and increase water storage on the floodplain, resulting in an overall smaller

downstream flood event.

Hydraulic modelling studies in south west England demonstrate that the planting of Forests across the floodplain could have a marked effect on flood flows (Thomas and Nisbet, 2004).

STUDY of the ROUGHNESS CHARACTERISTICS of NATIVE PLANT SPECIES in CALIFORNIA FLOODPLAIN WETLANDS

4. The role of Forest design and management

The different ways that Forest can affect flood flows are greatly

influenced by design and management factors.

Forest design determines species, age and structural diversity, as well

as the balance of forest cover and open space. Since the water use

effect is greatest for closed canopy conifer stands, the smaller that this

component becomes the lesser the potential effect on flood flows.

In terms of existing forests, the ongoing shift away from single aged

plantations to more mixed species and aged stands with a significant

component of broadleaves and open space, will act to ‘dilute’ the

present water use effect on flood flows. This is despite the greater

length of edge between young and old stands within a mixed-aged

forest, which enhances local turbulence and thus interception loss.

Research suggests that the edge effect is limited to a very narrow band

•Scale is a key issue when extrapolating the effects of forests to the

level of a larger catchment.

•Obviously, as the proportion of the area occupied by a forest

declines, its ‘signature’ will be progressively diluted by that of the

non-forest land cover.

• This is especially relevant when considering flood alleviation, with

most serious flooding problems arising well down the catchment of

major river systems.

• At this scale, forest cover often forms a relatively small proportion

of the total land area, limiting the potential to contribute to flood

defence.

•The diverse and mixed nature of the land cover is a key factor in the

UK and other neighboring places.

•The significant effect on flood storage and timing that was predicted by the hydraulic modelling study on the River Cary was achieved by a relatively small area of floodplain Forest, covering less than 2% of the total catchment area of 82 km2.

5. Importance of scaling

The impact of forestry on flood flows has been the subject of much national and international research. Earlier hydrological studies in the UK found little evidence of a 123 significant forest effect either at the headwater or at the large catchment scale. For example, an analysis of 35 years of flood flow records from moorland and forest research catchments at Plynlimon in mid-Wales found that upland floods in excess of the mean annual flood were scarcely affected by land use. A later study of the impact of extensive forest clearfelling in the same catchments also failed to find a significant change in peak flows (Robinson and Dupeyrat, 2003). The Natural Environmental Research Council’s Flood Studies Report of 1975 concluded from regional flood studies in Britain that the area of forest was not a significant factor in statistical relationships used for flood prediction. This was supported by McCulloch and Robinson’s (1993) review of the history of forest hydrology, which found that forests may reduce small floods but, generally, not extreme events.

Evidence base in support of forest controlling flood flows

The best protection for a stream is to be surrounded with a good buffer area of woods, shrubs, wetlands, and grasses to intercept contaminated runoff before it reaches the water. The less “groomed” this buffer area is, the more it can perform its normal functions, which include: •Protecting banks from erosion •Storing water and filtering it to ground water •Removing sediment and excess nutrients •Shading and cooling the stream •Providing organic debris for the stream’s food chain •Filtering out pollutants

Vegetation allowed to grow along the banks of streams and ponds prevents erosion and the related silting in and flooding during heavy rain events. Steep-banked streams require the hearty protection of shrubs and trees that provide shade, erosion control, temperature regulation and food sources for aquatic wildlife.

New Jersey Department of Environmental Protection,we worked with the Borough of Peapack-Gladstone and Amy S. Greene Environmental Consultants to restore a section of Peapack Brook, a trout

production stream, in the borough’s Rockabye Meadow Park.

Selection of Plant species

Plant strategies Avoid

Tolerate

millstonenews.com www2.mcdaniel.edu

mesa.edu.au www.shutterstock.com

Only grow during dryer seasons.

Grow roots above the water table.

Grow tissue that helps to get oxygen into roots.

Grow leafs and stems that are adapted to survive under water.

Root adaptations

Aerenchyma

– Long interconnected gas-filled chambers.

– Pathway for gas to diffuse from leaves to roots.

– Allows aerobic respiration to continue in the roots.

– Allows oxygenation of the soil surrounding roots.

mesa.edu.au

Root adaptations

Adventitous roots

– Roots that grow above the soil.

Shallow roots

Pneumatophores

– root tips that stick up from the soil surface.

gardeningstudio.com

Shoot adaptations

Shoot elongation

– Removes the shoots from complete submergence

– Mechanism

• loosening of cell walls

• Intake of water

• Synthesis of new polysaccharides

– Reduces the health of the plant once the water level recedes

www.ru.nl

Shoot adaptations

Hyponastic growth

– Growing leaves and shoots more vertically.

– Helps to implement the effectiveness of shoot elongation.

Submerged leaves

– Thinner cuticles

– Longer

– Physiological changes to cells

Signalling and hormones

Regulate the responses of plants to waterlogging and flooding

Ethylene – most important

Gibberellic acid

Abscisic acid

Hormones are interdependent

– Ethlyene decreases abscisic acid concentrations which leads to an increase in gibberellic acid

Summary Main problems of water logging and

flooding

– low oxygen in soil, gas diffusion in flooding

Avoid or tolerate

Low soil O₂ - aerenchyma formation

Flooding – shoot elongation, hyponastic growth

Ethylene is main regulator response to flooding

More in general, maintaining a vegetation buffer of at least 20m along river banks is very effective in controlling floods. Some of the most common hygrophilic tree species are being used to control floods, both in ponds and on the levees, are:

Poplars (Poupulus Nigra & Alba)

Willows (genus Salix, there are hundreds of different species to pick). By far the most used, they have a fantastic root system and can live with their root underwater for months!

There are several critical points to be considered in order to use vegetation to control floods: •Vegetation has to be maintained. Dead trees have to be cleared, tree stability especially on the river front has to be monitored •Aforestation is a critical process that sometimes can fail for no apparent reason. Good knowledge of the local ecosystem and vegetation association is required •A good variety of species has to be used in order to ensure the regeneration of the plants and the ecological quality of the area. Remember: a healthy environment is the first buffer against any natural hazard, and especially in river basins.

Among the shrubs the Elder (Sambucus Nigra) is very resistant and very important ecologically.

Elms (Ulmus )

Trees (Botanical Name - Common Name) Tall Deciduous Trees (50 feet or more in height at maturity) *Acer rubrum - Red Maple *Carya illinoinensis - Pecan Catalpa species - Catalpa *Fraxinus pennsylvanica - Green Ash *Liquidambar styraciflua - Sweet Gum Metasequoia glyptostroboides - Dawn Redwood *Platanus occidentalis - Sycamore *Quercus bicolor - Swamp White Oak *Quercus nigra - Water Oak Quercus palustris - Pin Oak *Quercus phellos - Willow Oak *Salix species - Willows *Taxodium ascendens - Pond Cypress *Taxodium distichum - Bald Cypress Medium Deciduous Trees (30 to 50 feet in height at maturity) Asimina triloba - Pawpaw *Betula nigra - River Birch *Carpinus caroliniana - Ironwood *Diospyros virginiana - Persimmon Gleditsia triacanthos - Honey Locust Magnolia macrophylla - Bigleaf Magnolia *Nyssa aquatica - Water Tupelo *Nyssa sylvatica - Black Gum *Quercus laurifolia - Laurel Oak Small Deciduous Trees (under 30 feet in height at maturity) Amelanchier arborea - Juneberry Chionanthus virginicus - Fringetree Cornus alternifolia - Pagoda Dogwood Halesia carolina - Carolina Silverbell Hamamelis virginiana - Witch Hazel Magnolia tripetala - Umbrella Magnolia Ostrya virginiana - Hop Hornbeam Styrax americanus - American Snowbell Evergreen Trees *Chamaecyparis thyoides -White Cedar *Gordonia lasianthus - Loblolly Bay Ilex cassine - Dahoon Ilex opaca - American Holly Magnolia grandiflora - Southern Magnolia *Magnolia virginiana - Sweet Bay *Pinus elliotti - Slash Pine *Pinus taeda - Loblolly Pine Sabal palmetto - Cabbage Palm

Plants for Damp or Wet Areas

Shrubs (Botanical Name - Common Name) Evergreen Shrubs Agarista populifolia - Florida Leucothoe Cyrilla racemiflora - Leatherwood Fatsia japonica - Japanese Fatsia *Ilex glabra - Inkberry Ilex verticillata - Winterberry Ilex vomitoria - Yaupon Holly Illicium floridanum - Florida Anise Leucothoe axillaris - Coastal Leucothoe Myrica cerifera - Wax Myrtle Osmanthus americanus - Devilwood Sabal minor - Dwarf Palmetto Deciduous Shrubs Aesculus parviflora - Bottlebrush Buckeye Aronia arbutifolia - Red Chokeberry Baccharis halimifolis - Groundsel Tree Callicarpa americana - American Beautyberry Calycanthus floridus - Sweetshrub *Cephalanthus occidentalis - Buttonbush Chimonanthus praecox - Wintersweet *Clethra alnifolia - Summersweet *Cornus sericea - Redtwig Dogwood Forsythia species - Forsythia Fothergilla species - Fothergilla *Ilex decidua - Possumhaw *Itea virginica - Virginia Sweetspire *Lindera species - Spicebush Rhododendron atlanticum - Coast Azalea Rhododendron viscosum - Swamp Azalea Rhodotypos scandens - Jetbead Rosa carolina - Carolina Rose Rosa palustris - Swamp Rose Sambucus nigra ssp. canadensis - American Elderberry Spiraea x vanhouttei - Bridal Wreath Spiraea Thuja occidentalis - American Arborvitae Vaccinium arboreum - Farkleberry Viburnum opulus - Cranberry Viburnum Xanthorhiza simplicissima - Yellowroot Zenobia pulverulenta - Dusty Zenobia

Groundcovers & Vines (Botanical Name - Common Name) Ajuga species - Carpet Bugle Aspidistra elatior - Cast Iron Plant Bignonia capreolata - Cross Vine Campsis radicans - Trumpet Creeper Convallaria majalis - Lily of the Valley Decumaria barbara - Wild Climbing Hydrangea Gelsemium sempervirens - Carolina Jessamine Hydrangea anomola petiolaris - Climbing Hydrangea Liriope spicata - Liriope Lonicera sempervirens - Trumpet Honeysuckle Smilax smallii - Jackson Vine Wisteria frutescens - American Wisteria Ferns (Botanical Name - Common Name) Athyrium filix-femina - Lady Fern Athyrium nipponicum - Painted Fern Cyrtomium falcatum - Holly Fern Dryopteris erythrosora - Autumn Fern Dryopteris filix-mas - Male Fern Matteuccia pennsylvanica - Ostrich Fern Onoclea sensibilis - Sensitive Fern Osmunda cinnamonea - Cinnamon Fern *Osmunda regalis - Royal Fern Thelypteris palustris - Marsh Fern Ornamental Grasses (Botanical Name - Common Name) *Arundo donax - Giant Reed *Carex species - Sedges Chasmanthium latifolium - Northern Sea Oats Schizachyrium scoparium - Little Bluestem Sorghastrum nutans - Indian Grass Spartina pectinata - Cordgrass

The best way to go, at least for flash floods, is to create a "Retention basin" with a dense vegetation canopy made of autoctonous riparian trees upstream the areas you want to protect. You will not only have the best flood protection system you can get but you will also create a highly valuable natural area, very important both for the riverine ecosystem and for the whole valley. These areas can even be used for recreation and tourism, if a good flood alert system is in place.

This Giant Wall Made From Plants Isn't Just Pretty: It Can Stop A Flood

The walls are alive in Victoria, London, where a new 21-meter-high vertical garden located on the side of a hotel contains 10,000 plants and 16 tons of soil—all in the name of flood

protection.

Los Alamos plants willows for flood recovery

Los Alamos plants willows for flood recovery The Laboratory's Corrective Actions Program (CAP) planted nearly 10,000 willows to help preserve the Pueblo Canyon wetland after damage from September 2013 floods.

•Plants and Forests offers a number of potential opportunities for flood control. •Research and experience indicates that those provided by the greater water use by trees and the forest sponge effect are largely restricted to the headwater or small catchment level. • Modelling studies suggest that floodplain forest offers the main way of ameliorating extreme flood events at the large catchment scale, although results remain to be tested in practice. •Overall, there appears to be significant scope for using woodland to help reduce flood risk, as well as to provide a wide range of other environmental, social and economic benefits. However, in order to achieve these, forest needs to be better integrated with agriculture and other land uses as part of a whole-catchment approach to sustainable flood management.

Conclusions

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QUESTIONS ARE WELCOME