*2.2.1. Hydrogeological conditions and derivation of hydrogeological parameters*

The groundwater model area is located at the northern part of the North China Plain (NCP), which is the largest alluvial plain of eastern Asia. The NCP is a basin with quaternary aged surficial deposits (loess, sand, gravel and boulder, silt and clay). According to the hydrogeo‐ logical profiles of Beijing the quaternary system in this region is fairly complicated. A great variety of different sedimentary facies exists with different thicknesses ranging from several tens of meters around the piedmont area to 150 - 350 meters in the northern central part of the NCP [9]. Groundwater is exploited in the layers of quaternary deposits, i.e. in the loose stratum/porous aquifers with high to very high water storage capacities. From the Taihang Mountains in the west to east there are two main geomorphological units in the model area: the piedmont plain below the mountain escarpments and the flood plain. In the piedmont plain the aquifers structure is coarse and becomes finer from west to east. In the flood plain the structure of aquifer is fine with silt sand, clay and silt interlay and in areas of ancient rivers and paleochannels the aquifer is composed mainly of gravels and coarse sands with good permeability. Therefore the distribution of groundwater in the Beijing region is inho‐ mogeneous. Regions of high abundance and high yielding porous groundwater aquifers are the piedmont plains and the northeastern districts of Miyun, Huairou and Shunyi whereas less yielding aquifers are found in the Yangqing and Tong districts. In the transition zone from the Taihang Mountains to the NCP the quarternary sediments with low thickness of e. g. some tens of meters are lying on the older rock formations of the regions.

In the mountainous districts unstable groundwater distributions were assumed in depend‐ ence on the form of the rocks with geological discontinuities (fractures, joints, dissolution features) and the groundwater flow. In the transition area from the Taihang and Yanshan Mountains to the NCP stratigraphic sequences of various ages ranging from archaean meta‐ morphic rocks to quaternary are documented in the geological and hydrogeological maps. A detailed description of the geological and hydrogeological conditions can be found in [10].

On the base of a conceptual geological model and a structured horizontal (2D) groundwater model, a horizontal and vertical structured 3D - groundwater model was developed describ‐ ing the saturated zone till approx. 200 m depth below ground surface (bgs.) in the area of the quaternary sediments of the NCP. In addition the borehole data from approx. 125 drill‐ ings situated in the model area were used in the groundwater model. Although a quite ho‐ mogeneous distribution of the boreholes was given, one measurement point represents an area of about 50 km2 which is only a rare database for modelling subsurface conditions.

There can be found strong variations in structure and thickness of the loose stratum sedi‐ ments in the model area. The evaluation of all data (borehole data, geological and hydrogeo‐ logical maps and profiles, ground water levels from observation wells, literature etc.) shows that the large number of the water bearing layers can be summarised in up to three essential ground water aquifers according to present knowledge on regional level. These aquifer sys‐ tems are from top to down:


industry and agriculture (see [8] for details). This parameterization issue is supported by

powerful geographical information systems (GIS).

28 Water Supply System Analysis - Selected Topics

**Figure 3.** Mesh of the 3D Finite Element groundwater model of the region of Beijing

*2.2.1. Hydrogeological conditions and derivation of hydrogeological parameters*

The groundwater model area is located at the northern part of the North China Plain (NCP), which is the largest alluvial plain of eastern Asia. The NCP is a basin with quaternary aged surficial deposits (loess, sand, gravel and boulder, silt and clay). According to the hydrogeo‐ logical profiles of Beijing the quaternary system in this region is fairly complicated. A great variety of different sedimentary facies exists with different thicknesses ranging from several tens of meters around the piedmont area to 150 - 350 meters in the northern central part of the NCP [9]. Groundwater is exploited in the layers of quaternary deposits, i.e. in the loose stratum/porous aquifers with high to very high water storage capacities. From the Taihang Mountains in the west to east there are two main geomorphological units in the model area: the piedmont plain below the mountain escarpments and the flood plain. In the piedmont plain the aquifers structure is coarse and becomes finer from west to east. In the flood plain the structure of aquifer is fine with silt sand, clay and silt interlay and in areas of ancient rivers and paleochannels the aquifer is composed mainly of gravels and coarse sands with good permeability. Therefore the distribution of groundwater in the Beijing region is inho‐

**•** Aquifer III in the depth area of approx. 120/140 m to 200/260 m bgs

The aquifers are separated by less permeable layers or aquitards, above all fine sands, silts and clays. It can be assumed that the three essential aquifers are not completely independent from each other, i.e. a groundwater exchange takes place between them in a certain range. Where low permeable layers or aquitards are absent or have a low thickness two aquifers can form a hydraulic unity as in the area of piedmont plains. Thus in the piedmont plains only one porous aquifer between the unsaturated loess top set layers and the bedrock was assumed. In regions, in which the separating layers have bigger thickness and larger exten‐ sion, local confined aquifers can appear. Because of morphology and evolution processes perched aquifers can appear within the loess deposits. All these local effects are summarised in the above mentioned three essential aquifers.

The piedmont areas of the Taihang Mountains and the Yanshan Mountains along the western boundary and the northern/northeastern boundary of the area are the areas where groundwater inflow into the plains contributes to the groundwater recharge of the confined and unconfined aquifers. Because of the multi-layered geological structure of the loose stratum in the model area, consisting of loess, alluvial loess, sand-gravel-cobbleboulder sediments with more or less mighty clay and silt inclusions, the details of hydro‐ geological conditions are complicated. Therefore the used spatial distribution of the hydraulic conductivity and specific yield (both important for good model results) are ad‐ equate phenomenological descriptions of mean values and not a detailed representation of local conditions in reality.

inflow did not disappear, but decreased from a long term mean value of about 0.7x109

precipitation rate of about 590 mm/a is in the range of 0.4x109 m3

asssumed to be directly dependent on the precipitation.

**Figure 4.** The groundwater inflow regime into the NCP

m3

is of about 0.3x109

ly in terms decades.

tion rate of 380 mm/a, for instance, the rain dependent inflow to 0.26x109 m3

only result from rainfall runoff from the mountainous domain. Therefore it was assumed a split of the horizontal groundwater recharge from groundwater inflow into the model area (see Fig. 4). One part is a rain-dependent contribution which in 'normal years', with a mean

dependency of the mean precipitation rate of the current year. In a dry year with a precipita‐

tribution the imagination is that a part of the precipitation of the mountain slopes infiltrate on the surface and percolate down to the bedrock basis. On the relatively impermeable bed‐ rock the water flows as shallow groundwater aquifer in the loose stratum with low thick‐ ness into the model area. The loose stratum depositions in the piedmont plains consist of boulder, gravels and sand with inclusions of local loess and loessloam lenses. These loose stratum depositions are well permeable and this inflow contribution from the mountains is

The second contribution to the horizontal groundwater recharge from the mountainous area

component corresponds to the part of the precipitation which infiltrates in the mountainous area through clefts into the deeper rock formations. The groundwater flow system in the bedrock consists of macroscopic structures and cavities linked with each other, as for exam‐ ple fracture networks, faults, layer joints, dissolution features and conduits etc. The ground‐ water inflow depths were assumed according to the distribution of the water bearing carbonate rocks, sandstones and crystalline rocks in the hydrogeological map of Beijing. These so-called deep inflows are not dependent directly on the precipitation and change on‐

/a and it was implemented deeper. Here the underlying idea is that this

/a could be observed by the Chinese partners. This amount of water could not

Model Based Sustainable Management of Regional Water Supply Systems

to 0.4x109 m3

m3 /a 31

/a. This value is scaled in

http://dx.doi.org/10.5772/51973

/a. For this con‐

The aquifer characteristics were determined mainly on the base of the interpretation and evaluation of the above mentioned borehole data. The borehole data represent the geologi‐ cal layers (boring logs) at single points. They show high variations from one point to anoth‐ er. In particular the hydrogeological parameters kf and S0 were deduced from these borehole data due to the following procedure:


On the basis of the derived values a fine tuning was realized in order to get minimal differ‐ ences between calculated and measured groundwater surface map.

The kf -values of the aquifers range from 2.0x10-3m/s in the region of the piedmont plains and the alluvial fan plains to 0.1x10-4m/s in the flood plains. The loose stratum depositions can be classified according to German Institute for Standardization Guideline 18130 as per‐ meable to very permeable.

In [12] a mean storativity in the range of 0.08 and 0.18 has been estimated. Due to hydrogeo‐ logical investigations of borehole data a regionalisation of the hydrogeological parameters could be performed, yielding a mean storativity of 0.13. The values of S0 changes from 0.19 (piedmont plains) to 0.03 (flood plains). This spatial distribution of kf - and S0-values was also a basis for the regionalisation of the inflow boundary conditions.
