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Landscapes, Ecohydrology &

FloodsUnderstanding of landscape ecology and ecohydrology for reducing

flood risk

Declan Hearne ENRM 230

What’s inside

Floods and landscapes

What evidence based tools can help?

How we can employed such tools?

What was found out and what are the implications?

Floods & landscapes

Flood risk in urban centers is increasing

Drivers of change are both global and local Climate change is triggering an increase in hydro-

meteorological hazards. Local land cover degradation, deforestation

urbanization and conversion of floodplains have all increased our vulnerability to hydrological hazards.

Floods & landscapes

With a series of devastating flood affecting the Philippines there is a drive to rehabilitate many of the upland degraded landscapes.

But to what extent can land use management really play in managing floods?

good forest cover reduces flood risk?

Study objectives

To understand how landscape ecology & ecohydrological principles can be applied to reduce flood risk.

to employ evidence based approaches that can help quantify understanding about the effect of different land uses in river basins

theory for guiding change

Ecology - living organisms have with respect to each other and their environment.

Landscape ecology - relationship between the spatial and temporal arrangement of ecological elements and processes (e.g. the flow of energy, materials & individuals in the environment)

Ecohydrology - considers the functional interrelations between hydrology, ecosystem processes and their biota.

Ecohyrdology Zalewski (2010)

based on "dual regulation" and harmonization of landscape ecology with human needs, such as flood mitigation, food and energy production, transport and recreation;

Dual regulation: regulation of biota by altering hydrology and regulation of hydrology by shaping biota.

Methods

Review of secondary data (maps, bio, physical and social)

Conduct of rapid field assessments

Conduct of GIS based land assessments Landscape classification Landcover elements (matrix model, based on CPDO

indices) Landcover change from 2002 – 2010 Estimation of landscape roughness

How we employed the tools?

Assumptions & limitations

Patches of trees can act as filters in the landscape and can have impacts at the river basins scale

No ground verification of landscape assessments

Low definition used in identification landscape element types (could not differentiate between brush, shrub and open forest - so all are classified as one land cover type Patch density, Edge density, or number of classes are not

established

The method used for scaling up manning co-efficient to a landscape scale is likely increase the potential for error in final roughness estimations

Forest and Floods

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ResultsWhat was found out

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Overview of results3 sub-landscapes

3 Sample areas analyzed

•matrix and patch make up•Land cover change

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Defining landscape

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Defining landscape

sBase Map: MGB

Geohazards Map 2004

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Defining landscape

sDelineation of

catchment and high erosion areas

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Defining landscape

sDelineation of

landscape based on hazards, and field

observed socio, production and ecological uses

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Sample AreasSample Areas of approx 2 km2 was used to measured predominate landscape elements in each landscape

Matrix was calculated for each sample area

M = SA - (P1+P2+ P3 + P4 … etc)

Where M is the matrix landscape elementSA is the total area of the sample areaP is the total are for individual patch types (e.g. P1 is open forest, P2 is grassland etc)

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SA1: Socio production landscape

Remnant Patches (OCF)

Disturbance Patches (G)

Introduced Patches (BUA)

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Open Canopy

Grassland

Built Up Areas

Matrix TP

SA2: Riparian landscape

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Sample Area 3

Manning Coefficient

Manning landscape estimate = n* % area cover

Riparian Landscape = 0.011Socio production L = 0.010Lower RL= 0.009

The coefficient is mainly a property of the ground surface texture and the changes in water surface elevation.

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Discussionwhat are the implications?

Largely fragmented landscapes

Matrix landscape is tree plantation/ agriculture (aligned with CLUP)

Remnant forest patches ranged between 14 – 20%

Social production landscape has lowest observably PD

Landscape change is subtle, but real

Land cover change is not substantial if taken over the total river basin, but 18.4% increase in built area in lowest portions of the riparian

landscape (RL) 7% reduction in open forest in the upper sections of the RL Continued degradation was obvious during field assessments

The extensive riparian corridor is absent from CLUP

Manning coefficient demonstrated the the RL has highest potential to slow water run off from the landscape

Recommendations

Protection of the remaining open forest stands and reforestation efforts to reduced flood risk downstream would be most efficient if they are targeted within the Riparian Landscape.

the use of down-slope riparian buffers can attenuate rapid run-off at the local scale

to add value to protection and reforestation interventions water water quality and biodiversity objectives should be included

Land use management will never stop flooding, the goal must be to able to live with floods and not to eliminate them.

Gaps…the original paper did not resolve

the extent to which floods can be mitigated through land use management (10%, 20%, 30% reduction in flood intensity???)

Flood intensity needs to better understood when considering landscapes measures for reducing flood risk (little observed impact in extreme events!)

Analysis of soils is critical to improve infiltration or sponge effect (targeted planting should be in sensitive soils.)

Species best suited for increasing hydrological roughness needs to be established.

methods to ensure sapling can reestablish themselves in eroded and degraded riparian zones.

Study objectives

To understand how landscape ecology & ecohydrological principles can be applied to reduce flood risk.

to employ evidence based approaches that can help quantify understanding about the effect of different land uses in river basins