蒙古Unkheltseg盆地地质间断的三维地下水流数值模拟-英文版

ORIGINAL ARTICLE

3-D numerical groundwater flow simulation for geological

discontinuities in the Unkheltseg Basin, Mongolia

Yohannes Yihdego

•

Cara Danis

•

Andrew Paffard

Received: 8 August 2013 / Accepted: 9 September 2014 / Published online: 21 September 2014

 Springer-Verlag Berlin Heidelberg 2014

Abstract Groundwater models which realistically repre-

sent the hydrogeology of a complex system, like the

are available in the public domain and the model presented

here aims to address this problem. This basin is uniquely

geologically controlled and a key water supply resource for

future economic development in the Taikh Valley. Com-

mercial exploration projects have produced the high-qual-

ity geological and hydrogeological data gathered,

necessary for successful model simulation at a basin-wide

scale. Using the ‘‘DRAIN Package’’ and ‘‘Fracture-Well

Package FW4’’ in MODFLOW-SURFACT, the spatial

discretization necessary to fully represent horizontal and

Geological discontinuity  Mongolia

Introduction

Groundwater resources play a vital role in Mongolia’s econ-

omy and the industrial and domestic water demand is mainly

met from groundwater sources; about 80 % of the total con-

sumption is from groundwater (Hasiniaina et al. 2010).

Modelling of groundwater resources in Mongolia, which is

also common elsewhere, is challenging, due to limited infor-

mation, both published and government data, historical reli-

ance on simple analytical assessments and complex

Project), havebegun presenting 3-D numerical simulations for

resource estimation and using these simulations to calculate

resource lifespan and extraction limits, something not possible

with the current analytical methods used in Mongolia.

Over the last few years, a number of discussion papers

have addressed the issue of how models can best serve the

process of decision support. Previous studies (e.g. Gupta

et al. 2012; Kresic and Mikszweski 2014; Nordstrom 2012;

Simmons and Hunt 2012; Voss 2011) have addressed the

extent to which the model’s parameters should be adjusted

plexity is most difficult where predictions required of a

model are only partially constrained by historical data

(Doherty and Simmons 2013).

Snowy Mountains Engineering Corporation (SMEC),

Sydney, NSW 2060, Australia

e-mail: yohannesyihdego@gmail.com

Environ Earth Sci (2015) 73:4119–4133

DOI 10.1007/s12665-014-3697-4

2008; Shan et al. 1995). Whilst our interpretation of the

faulted aquifer remains linear in nature, parameter esti-

mation by numerical simulation highlighted the presence of

hydraulic barriers associated with the faults. These barriers

are readily apparent in the constant discharge test data.

Fracture zones and faults have long been identified as

having significant influence on groundwater flow and

transport because of their contribution to altering the

effective permeability of the aquifer. For this reason, there

have been numerous investigations aimed at describing a

may exist because faults are often observed to act both as

conduits (Huntoon and Lundy 1979; Pimentel and Hamza

2014) and as barriers (Ran et al. 2014; Rojstaczer 1987)to

flow. Thus, broad generalisations regarding the influence of

faults are difficult to make.

region was initially based on yields from pumping tests

(Battumur 2009), interpreted analytically by the Cooper–

Jacob simplification of the this approach (e.g. Freeze and

Cherry 1979; Fetter 1994). This estimation indicated that

the Unkheltseg Basin as a mine water supply source for

Bayan Airag Exploration.

The Unkheltseg Basin

The Unkheltseg Basin is located approximately 930 km

west of the Mongolian capital Ulaanbaatar, 250 km south

of the border with Russia, in Zavkhan province, Erdene-

khairkhan Soum in a region characterised by steep moun-

tainous terrains and wide valleys. The region is dominated

by reverse faults, striking parallel to the mountain ranges,

which have significant vertical displacement, up to 100 m

The discharge from the basin system into the southern Tost

Basin is controlled by the permeability and hydraulic

conditions of the barrier as groundwater discharge occurs

across a geological discontinuity, which is presumed here

to be a fault uplifted basement. Therefore, there is no direct

hydraulic connection between the basin and the southern

Tost Basin and this groundwater storage–discharge rela-

tionship cannot be easily handled by simple analytical

equations or 1-D or 2-D numerical simulation programmes.

The challenge with 3-D numerical simulations is to pro-

In watershed models, the subsurface-saturated domain is

often represented by a linear, or non-linear, storage–dis-

charge function (e.g. Fiorillo 2011; Kampf and Burges 2007;

Rupp et al. 2009; Singh and Woolhiser 2002; Wenping et al.

2011

with a physics-based description of saturated flow, but

assumptions made thereafter (e.g. constant head gradient or

successive steady states) lead to a single-valued storage–

discharge function (e.g. TOPMODEL; Beven and Kirkby