Prof. Dr. Rudolf Liedl Dipl.-Hydrol. Marc Walther

FACULTY OF FORESTRY, GEOSCIENCES AND HYDROSCIENCES, DEPARTMENT HYDROSCIENCES, INSTITUTE FOR GROUNDWATER MANAGEMENT

TU Dresden, April 25, 2012

IWRM (MWW16): Groundwater Management

Prof. Dr. Rudolf LiedlDipl.-Hydrol. Marc Walther

FACULTY OF FORESTRY, GEOSCIENCES AND HYDROSCIENCES; DEPARTMENT HYDROSCIENCES, INSTITUTE FOR GROUNDWATER MANAGEMENT

TU Dresden, April 24, 2012 Liedl / Walther transparency 2 of 37

Contents• groundwater mana-

gement issues in theAl-Batinah region

• conceptual model and compilation ofdata

• density-dependentmodelling

with acknowledgmentsto A. Gerner, J. Grund-mann, and A. Philipp



Groundwater Management Issuesin the Al-Batinah Region



Study Region – Al-Batinah Coast, Northern Oman



Overview of Study Area• three wadis in northern

coastal area along Gulf ofOman

• highest population density ofOman

• strong economical and popu-lation growth

• highly productive soils

• large amount of agriculture

• high water demand for irri-gation purposes

• Groundwater is the onlyfreshwater resource.

• extraction of groundwater(pumping wells)

• lowering of the groundwatertable

• As a result, saltwater fromthe Gulf of Oman intrudesinto the subsurface.



Traditional Ways of Irrigation – Aflaj System



Modern Irrigation



Challenges for Groundwater Management• quantitative constraint:

rapid decrease of groundwater level due to overpumping / mining of groundwater (since 1970s)

• qualitative constraint: reversion of groundwater gradient

marine saltwater intrusion

Tasks (from “groundwater‘s perspective“):

• protect and secure local (ground-)water resources in the frame of an IWRM (links to other activities within a comprehensive research initiative)

• develop and apply a three-dimensional, density-dependent groundwater model as an important tool to quantify – the movement of the freshwater-saltwater interface – impacts of variable groundwater recharge and changes in water regime

(e.g. climate change) – impacts of water usage practices in agricultural irrigation: pumping

schemes, crop patterns, irrigation techniques …

define and evaluate realistic scenarios accounting for an optimized groundwater usage reduce marine saltwater intrusionsupport recommendations (“Who should get how much water?”)



Groundwater Quantity

• decreasing groundwater table

• groundwater abstraction > groundwater recharge (“groundwater mining“)



Groundwater Quantity

• aquifer storage change based on decreasing groundwater levels

• decrease of ca. 1550 Mio m³ in 25 years

• average decrease: ca. 62 Mio m³ per year



Groundwater Quality

saltwater intrusion in the studyarea (2000)schematic representation



Seawater Intrusion Lab Experiment

26 cm

53 cm

basic experimental setup according to Goswami et al. (2007)



Conceptual Model and Compilation of Data



wadi runoff(flash floods)

sea

saltwater intrusion

extraction wellsnear the coastline

irrigated agriculture(most important)

rainfall

recharge dam for artificial ground‐water recharge

infiltration

Hadjar mountain Batinah plain Coastal zone

P(x,y,t)

Aflaj(3 types)

surface runoffQi(x,y,t)

irrigated oases agriculture

Groundwater model domain

Qgwn,m

Qin

Qa

Qw

Qinf

ET

ETET

ETR

Qp

Qw,d

Qgwn,w

Qs

QloSea losses

Qa

Qw,d

P(x,y,t)

ETR

Processes and Interactions

Grundmann (2011)



Surface Water-Groundwater Interactions

Surface Water 3: Direct Recharge due to Rainfall

Groundwater

Surface Water 1:

CatchmentModelling

in theMountainous Area

(Hadjar);

Mountain FrontRecharge

Surface Water 2: Indirect Rechargedue to Wadi Runoff & Recharge Dams

Qwadi

Coastal Zone

Agriculture

Abstraction& Percolation

from Irrigated Areas

Rainfall: Analysis, Areal Precipitation, (Stochastic Simulation)

Mountains Foothills Plain Coastal Zone

SeawaterInterfaceGrundmann (2011)



Uncertain Extent of Recharge Areas

• Recharge areas differ from surface catch-ment areas!

• Fuzzy recharge areas(with bandwidth)

Gerner (2011)



Mountain Front Recharge – Overall Approach

rainfall input

spatially distributedrecharge quotas

Raster-basedrecharge volumes

water use ofmountain oases /

aflaj

spatial overlay

GW modeldomain

↑flowpath

↑mountain

front↑

mountains

uncertain contribution to the two GW Plumes

Gerner (2011)

one boundary condition

of the GW Model



Water use ba-sed on Natio-nal Aflaj In-ventory:

• approach: 2700 mm/a related to cropped area

• evaluation: probably over-estima-ted

Options for future refinement:• site-specific potential evapotranspiration ETP (Siebert, 2007)• database (crop patterns & climate data)

Water Use of Mountain Oases / Aflaj System

Gerner (2011)



Wadi Runoff and Recharge Dams

Q(t)

t

Q(t)

t

Dam inflow

Dam outflow

Q(t)

tRecharge

Upstream channel Recharge dam Downstream channel

Flow Path

Recharge

dam simulation toolSix, 2011

wadi channel routingwith zero-inertia

approach(analytical) plus

infiltration;free lower boundary

Philipp, 2010

wadi channel routingwith zero-inertia

approach(analytical) plus

infiltration;free lower boundary

Philipp, 2010



rainfall

Direct Recharge Due to Rainfall in the Plain

• ICM Ma’awil (2004) 25 % of aerial P in the plain

comparing literature might suggest lower values (5 to 10 %)assuming an invariant relative quota for direct recharge does not account for all intensities of P!surface runoff / dynamics flow paths for high(est) intensities? Lateral flow paths? Ephemeral shallow water lenses?

• Possible future work checking for estimation of direct rechargefield / site infiltration experiments under different intensitiesmodel/simulation based experiments



Groundwater Recharge Assessment

0

20

40

60

80

100

120

140R

echa

rge

(Mm

³/a)

55.5 8 63.5Range 75 17 92

103.5 29.5 133

Mountain Recharge (incl. Oases use) Recharge direct/indirect OVERALL GW RECHARGE

Groundwater Recharge Assessment

Gerner (2011)



Density-Dependent Modelling



Code Selection

• OpenGeoSys (OGS) is an open-source finite-ele-ment code developed at Helmholtz Centre for Envi-ronmental Research (UFZ), Leipzig.

• It addresses many THMC processes (thermal, hy-draulic, mechanical, che-mical) incl. coupling.

• Further information at www.OpenGeoSys.netor in Kolditz et al. (2012).



Benchmarking Problem



Comparison With Experimental Results

comparison of isolines for Crel = 0.5

concentration & velocity field (OGS simulation)



Model Domain

• steady-state modelling (1970ies)

• transient modelling (saltwater intrusion since then)

30 x 40 km²25 layers300‘000 elements



(Hydro-)Geology

fluviatile,marine, andaeoliandeposits



(Hydro-)Geological Data Compilation

• various sources like tables, figures, drilling logs …

• meetings / conversations with Omanihydrogeologists

• 12 major „materials“(e.g. gravel, silt, clay, bedrock …)

Base of alluvium from boreholedata, after Lakey (1995)



Hydraulic Conductivity

data interpolation by employing a modified inverse distance method

Blue = high permeabilityRed = low permeability

Thicknesstotal ~ 400 mcoast ~ 50 mtrough ~ 250 m

thin coastal aquifer

“Ma‘awil trough“



Steady-State Groundwater Abstraction

Dug wells Borehole wells

Estimate of total abstraction rates until 1970s: Q ~ 40 Mio m3/a(Ministry of Agriculture and Fisheries Technical Report, 1992; Al-Shoukri, 2008)



Steady-State Flow Field

velocities1 m/d –0.1 mm/d

Red = high velocityBlue = low velocity



Steady-State Calibration

• Steady-state calibration was performed for the situationin 1974.

• automated calibration withPEST (Parameter ESTimati-on)

• PEST is a calibration tool wi-dely used in groundwaterapplications.

• Only 14 groundwater levelobservation series startingin 1974, many starting later.

• some results:

inflow ca. 68 mio m³/aextraction ca. 37 mio m³/a



Saltwater Intrusion Scenario for Steady-State Flow

total inflow~ 70 mio m³/a

abstraction~ 40 mio m³/a



Density-Dependent 3D Simulation



First Comparison With Measurements

Salinity at 10 m below water surface

Simulation Measurement (Ministry of Regional Municipalities, Environment and Water Resources, 2005)



An Outlook to Transient Calibration

Groundwater level difference (simulation – measurement)



Summary and Outlook

• Groundwater assessment andmanagement are important com-ponents for IWRM in the Al-Batinahregion

• Presented results are preliminary –there is much work to do!

• improved calibration & validation(also vs. salinity data)

• (future) scenario simulations forbest / worst cases

• cross-checking of GW results withfindings from other investigations

What remains essential:

• continuous data collection: groundwater levels, salinity measurements, isotope analysis, drill logs …

• proper data management:i.e. gather, collect, evaluate, store, handle

• good cooperation at the “IWRM table“

Thank you verymuch for your

attention!

Prof. Dr. Rudolf Liedl Dipl.-Hydrol. Marc Walther

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