Biogeomorphology.scherm

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There is a well known saying that ‘God created the earth but the Dutch created the Netherlands’. This saying

may be true for the situation since the late middle ages but it is certainly untrue on a longer timescale. The

formation of the Dutch coast during the Holocene has been the result of an interaction between sea trans-

gression and the deposition of marine and fluvial sediment. A wedge-type deposition was formed on the

Pleistocene substrate up to 30 m in height! In this process peat formations have played an important role. In

the low-lying areas a fast peat growth rapidly covered the substrate and thereby promoted the availability

of sediments for the adjacent coast. Natural processes destroyed peat formations quickly and initiated a

new cycle. This 'breathing' of the coast shaped the Netherlands to its present form. This is a clear example of

the influence that biology (plant growth and peat formation) can have on geomorphology1

.

The effect o geomorphology on biology is well known.

Habitats o species (their living environment) are to a

large extent determined by physical actors such as in-

undation requency, flow velocity, depth and sediment

characteristics.

Interactions such as these orm the area o interest o

biogeomorphology. Biogeomorphology or, ecomorphol-

ogy, is a research area where biology, ecology, hydrolo-

gy and morphology come together. Biogeomorphology

o water systems is the discipline that treats hydro-morphology and biology together as one single subject.

In the latter years there is a growing awareness o

the impact o biological processes on geomorphology

and vice versa. Moreover there are a growing number

o clients that come to Deltares / Delf Hydraulics

with questions related to the interdisciplinary field

o biogeomorphology. Thereore, biogeomorphology

has become one o the ocus areas at Deltares / Delf

Hydraulics.

1People working in the fields o c ivil engineering and hydrology use the

term morphology instead o geomorphology. However, or biologists

morphology has a different meaning. To avoid conusion the term

geomorphology is used.

Aerial view o the dune breach o Texel, The Netherlands

Biogeomorphology



Deltares - Geo-engineering2

Deltares / Delf Hydraulics and biogeomorphology

To perorm biogeomorphological studies, or multidis-

ciplinary studies in general, there are two important

boundary conditions that have to be satisfied:

1. there needs to be a strong knowledge base in the

underlying disciplines, and

2. the underlying disciplines have to be well integrated.

During the more than 80 years o her existence,

Deltares / Delf Hydraulics has built up a consider-

able amount o knowledge and experience in the fields

o hydraulics, hydrology, morphology, water quality

and ecology, both in resh water and coastal marine

systems. This know-how has been put to use in a broad

variety o projects ranging rom harbour and dam con-

structions to coastal management studies.

The second condition is ofen underestimated, but is

equally important as the first.

Deltares / Delf Hydraulics provides the perect envi-

ronment or a ruitul interaction between disciplines:

there is no division between people with different

expertise but a division along ‘system lines’ such as

the marine and coastal system and the inland water

The Drowned Land o Saefinge, the Netherlands

system. This allows or an optimal communication

and co-operation o the different disciplines to tackle

problems in the most effective way.

Besides the above mentioned vital boundary condi-

tions, Deltares / Delf Hydraulics has a unique combi-

nation o expertise in highly sophisticated numerical

models, a variety o experimental acilities and fieldmeasurements.

Biogeomorphology at Deltares / Delf Hydraulics deals

with problems and questions on:

1. The incorporation o biological processes in

morphological modellingand biogeomorphological

experiments

2. The effects o morphological changes on biological

communities: impact studies

3. Management o water systems

research issues

biological orcing o hydromorphological modelling

Given the existence o interactions between geomor-

phology and biology, morphological models can be

improved by implementing routines which describe the

effects o the biological communities on the morpho-

dynamics. The research issues that are addressed and

related to this topic are:

• The eects of biological communities on hydromor phology through near-bed velocity, roughness, silt

trapping, biostabilisation and bioturbation. Both on

intertidal areas (salt water systems) and floodplains

(rivers).

• The relevant temporal and spatial scales and scale

interactions.

• Process oriented research in experimental facilities

ocusing on bio(de)stabilisation, sediment/water

exchange and sediment trapping or uture model

development.

impact studiesThe impact o human intererence on water systems

may lead to morphological changes. These may have

effects on a biological community or a single species.

The research issues here are:

• The denition of abiotic factors governing biological

communities, considering lie stages, habitats and

reproductive strategies (timing and scales).

• The denition of thresholds for the occurrence of

different habitats/ecotopes.

• The quantitative assessment of the relations

between governing abiotic actors and biological

communities or single species.



Deltares - Geo-engineering 3

management of watersystems

Management o water systems deals with: saety, the

variety o users and preservation o nature.

The modern concept o management considers all

these aspects. Research is done on:

• The mapping of physiotopes/ecotopes based on

easily quantifiable parameters.• The development of models to predict ecological

changes.

study approach

Given the broad spectrum o problems and research

areas there is no single methodology applicable. To

illustrate the approaches used a number o projects are

presented here in some detail.

Humber project (2000)

This work was part o a large English research pro-

gramme on estuaries led by HR Wallingord (UK: MAFF/

DEFRA, EA plus EN project). This project orms a good

example o the merger between morphological and bio-

logical expertise present at Deltares / Delf Hydraulics.

The long term (50 years) morphological developments

in the Humber estuary were modelled using the hybrid

model ESTMORF. The effects o these developments

on the physiotopes in the estuary were ‘modelled’ by

considering the changes in three physical actors. It

was ound in previous studies that each combinationo these actors defines a physiotope. The physiotope

model was validated with yearly data on macrobenthos

collected by the Environment Agency since the late

seventies. The conclusion was that overall there is a

good fit between predicted physiotopes and the pres-

ent day distribution o macrobenthic assemblage.

intertidal flat classification (1999)

In the European INTRMUD-project a methodology has

been developed to generate a set o abiotic and biotic

parameters or a qualitative intertidal flat classifica-

tion. When complete, such a classification scheme

can be used to (roughly) assess missing parameters.

Once it is clear to which type a intertidal flat belongs,

as deduced rom the known parameters, the ranges o

values or the missing parameters can be inerred rom

the classification scheme. This is based on the assump-

tion that all intertidal flats belonging to the same type

have parameters in the same ranges. In this way the

classification scheme can also be used as a qualitative

tool to predict changes caused by variations in some o

the descriptive parameters.

The general methodology to get to a classificationscheme is:

1. Identiy a set o governing parameters and their

discriminating threshold values. This is done

studying a single flat, in this case the Molenplaat in

the Western Scheldt Estuary in the Netherlands.

2. Establish the relation between these and ‘easy-

to-observe’ parameters, the so-called “Rules”.

3. Find out i parameters that are difficult to assess can

be inerred by combinations o other parameters.

4. Extend the data set to other intertidal flats to

complete the scheme.

the effect of submerged vegetation on turbidity

(1997-1999)

Besides large scale modelling and management proj-

ects, Deltares / Delf Hydraulics also perorms more

undamental studies within the field o eco-morphol-

ogy. For the Institute or Inland Water Management

and Waste Water Treatment (RIZA-RWS) a study was

conducted on the influence o submerged vegetation on

hydrodynamics and turbidity levels in Dutch Lakes.

An extensive set o experiments were perormed in the

tidal flume at Deltares / Delf Hydraulics. The effect o

natural and artificial vegetation on flow velocity, tur-

bulent intensity, suspended sediment concentrations

and wave heights was measured. The results were used

to calibrate and validate a 1-DV advection-diffusion

model adapted to incorporate submerged vegetation.

Experimental data in combination with the model

results gave valuable insight into the phenomenon

o clear water above a vegetation field as commonly

observed in the Dutch lakes.

An example how biology is influenced by morphology



relevant experience

• An experimental study on biogenic gas generation in

sediment storage depots and its effects on the

volume o the stored mud and on bottom erodibility,

started in 1996.

• A study on cyclic rejuvenation of oodplains or on

the mutual interaction between hydromorphology

and the development o vegetation, 2000-2003.

• Development of an ecomorphological module for the

Western Scheldt or long-term prediction o morpho

logical impacts (1998).

• Development of a Nature Module for analysis of

ecological value and species succession on and near

land reclamation works (1999).

Vegetation

-4.00 0.00 4.00 8.00 12.00position [m]

0.00

20.00

40.00

60.00

A v e

r a g e w a v e h e i g h t [ m m ]

Exp. 1; natural vegetation

Exp. 2; long artificial vegetation

Exp. 3; short artificial vegetation

The effect o submerged vegetation on wave height

• An experimental study in the tidal ume on the

effects o underwater vegetation on turbidity and

hydrodynamics, 1997-1999.

• A denition of the inter-relations between physical

actors and benthos on an intertidal flat in the West

ernscheldt with different approaches, 2000-2001.

• A study on the eects of the construction of the

seaward extension o the Rotterdam harbour on the

biological communities o flat fish and herring, 1999.

The Konkure river in Guinea

• An assessment of the environmental impact of a

dam construction on the Konkure river, estuary and

adjacent coast in Guinea, 2001.

• A study of the long-term morphological development

o the Humber estuary in combination with an

ecological assessment, the Habitat Evaluation Proce

dure (HEP), 2000.

• The denition of measuring tools or indicators for

the quantification o ‘geomorphological quality’, with

the aim o monitoring water systems and

quantiying their ‘morphological deterioration’, 2000.

• A pilot experimental study on the eect of worms

and diatoms on the bottom stability o mud depots,

2000-2001.

• A large-scale management study of the rivers

Pannerdens Kanaal, IJssel, Waal and Neder Rijn in the

Netherlands with the aim o finding a balance

between saety rom floods and natural values,

2000-2001.

P.O. Box 177

2600 MH Delf, The Netherlands

[email protected]

www.deltares.nl

Biogeomorphology.scherm

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