PEATLAND DRAINAGE IMPACTS ON HYDROLOGY

21.1.2014

Bjørn Kløve

Process and Environmental Engineering Department Water Resources and Environmental Engineering Laboratory

bjorn.klove@oulu.fi

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PEATLAND DRAINAGE IMPACT ON

HYDROLOGY

• Changes at catchment scale

• Changes in peat soil

• Changes in hydrology • initial changes

• drainage at steady state

• afteruse and hydrology

• Special topics floods, drought and snow melt

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Peatland forestry

COMPLEX DRIANAGE PATTERNS

HYDROLOGICAL CHARACTERISTICS OF

PRISTINE PEATLAND CATCHMENTS

•Upland forests and peatland interactions

•Ponds, springs, streams in complex

interactions

•Groundwater, precipiatation (rain and

snow) and cacthment runoff inflows

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CLASSICAL CONCEPTUAL MODELS

• Fen Bog

• Peatland hydrology is often a combination of these concepets

including hillslope processes

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P8

GW and SW inflow SW/GW

P

DETAIL PEAT AND WATER FLOW

• Flow high close to the surface

• Flow can occure in erosion channels even, so water can flow

even in well decomposed peat layers

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Overland flow/flow in channels

Flow in porous media (Darvy flow)

Preferential erosion channels

GW

HILLSLOPES AND INTERACTIONS

21 January 2014 10

Aquifer

Aquitard

Peatland

Precipitation

Surface runoff

Groundwater

PEATLAND HILLSLOPE HYDROLOGY?

KIITOS

Björn Klöve,

19.4.2012

SNOW ACCUMULATION AND MELT

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SNOW, FROST AND SNOWMELT

SNOW AND MELT

• Drains probably result in uneven distrubtion of snow (as

more snow in ditches)

• Snow melt intensity and soil cover

• Bare peat result probly in higher melt intensity (swhen

snow partly melted)

• Forests decrease melt rates

• Open field have high melt rates

• Pristine peatlands probably also have high melt rates

• Frost result in lower K values and snow melt runoff as

overland flow

• Snowmelt runoff can be low in

nutrients from drained peat soilx

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IMPACT OF DRAINAGE ON HYDROLOGY

• Pristine Drained

• 3D flow 2 D flow

• Topography driven Drain driven

• Flow in surficial layers Flow through decomposed

peat

• Overland flow-runoff Infiltration-runoff

Drainage influence flow direction!

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GROUNDWATER LEVEL AND SOIL PROPERTIES

• On average the GWL depends on net rainfall, K and pF (soil

hydraulic properties)

• Low K results in high GWL

• IF little effective porosity (special pF curve shape) then GWL

fluctuate easily 21.1.2014

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P ET

RUNOFF AMOUNT?

In Finland on average P = 600 mm and ET = 300

mm (100-400 mm), R = 300 mm

Land cover changes:

- Cutover peatlands (no vegetation) ET? - Bare soil maximum maybe 100-200 mm?

- Forested peatlands ET depends on LAI and

climate - Young stands and mature stands ET (200-500 mm?)

- North 150-200 mm and South 250-350 mm

- Arable lands (yield depends on ET) - North and South 200-300 mm?

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No major changes in runoff volumes

Volumes increase on cutover peatlands

Volumes reduce with dense plant cover

FLOW VARIATION (LOW AND HIGH FLOWS)

• Low flows depend on the amount of groundwater flow to the

peatland (natural and pristine)

• Impacts of drianage on low flows form peatlands is not well

studied, but drianage could perhaps reduce low flows dending

on impacts on ET?

• Impacts on peak flows • Reducing factors: drinage increase unstaurated soil, infiltration

control

• Incresing, due to intense drain network, also roads and

preparation of main channels will increase runoff as less flow

resistance is provided (not much studied)

• The impacts of drainage on flow variation probably not so

significant and case dependent 21.1.2014

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Pristine Impacted

DOWNSTREAM CHANNEL CONTROLS

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CONCLUSIONS

• Peatland hydrology measurements often difficult to carry

out and there is still a lack of research on the topic

• Peatland hydrology often complex where different upland

processes, channel controls, and interactions with surface

and groundwater are present

• Drainage changes soil properties and flow patterns

resulting in more water beeing infiltrated through the soil

• Drainage networks chnage flow routes

• Other hydrological changes are:

• Changes in total annual runoff depend on vegetation

cover

• Changes in low flow might occur

• Changes in peak flows case dependent (overestimated

in old litterature, but currently considered quite

minor) •

•

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Thank you for your attention

EC 7FP, Academy of Finland, VALUE DP, MMM, EAKR, MVTT, Renlund, Thule, Vapo

Oy, etc