*2.2.2. Derivation of timedependent groundwater recharge and exploitation data*

In order to determine the time-dependent groundwater recharge and exploitation we follow the subsequent procedure:


The first task in setting up models covering the water resources of an area of this size is to construct a water budget. The water budget is a theoretical device that supports struc‐ turing the water resource system and identifying the most important water fluxes. Here fluxes into and out of the system has to be collected as well as the water fluxes within the model area. The intension must be to realize the relation of water fluxes to each oth‐ er, to quantify them, separating the more important from negligible water fluxes and to estimate the error that happens due to neglecting them. Since most of the quantities in the water budget are not independent from each other, the quantification of the water budget must be an iterative process. Fig. 5 illustrates the water budget of the region of Beijing. All the before mentioned fluxes are entried. The width of the arrows corresponds to the quantity of the fluxes.

Since the groundwater model is spatially distributed the input data for the groundwater recharge and the exploitation have to be spatially distributed as well. The above men‐ tioned water budget can be regarded as a lumped parameter model for the whole region. The next step is to relate these data to locations by adapting the water balance with re‐ spect to specific regions.

**Figure 5.** Water budget of the region of Beijing

i.e. irrigation rates (*IRR*) for agriculturally used areas.

Regionalization of the water budget means to adapt and evaluate the balance equation

for each of these classes. It denotes *P* the precipitation rate, *GWR* is the groundwater re‐ charge, *ET* the evapotranspiration *SWR* corresponds to the surface water runoff. There are some quantities which are relevant for every class, like infiltration and there are some which are specific for a certain group. And for other classes additional quantities have to be added,

*P GWR ET SWR* = ++ (5)

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33


**Figure 5.** Water budget of the region of Beijing

The total horizontal groundwater recharge (inflow) ranges from 0.55 to 0.75x109 m3

*2.2.2. Derivation of timedependent groundwater recharge and exploitation data*

since none of the components can be measured directly.

an idea which fluxes are in which order.

the subsequent procedure:

32 Water Supply System Analysis - Selected Topics

dependent quantities.

to the quantity of the fluxes.

spect to specific regions.

**•** agriculturally used and irrigated areas,

paved areas,

**•** water areas and

**•** non-cultivated areas

quantitative split is to some extend arbitrary and based only on plausibility considerations

In order to determine the time-dependent groundwater recharge and exploitation we follow

**1.** It starts with stating a long term mean value budget for the considered area for getting

**3.** Finally the temporal distribution is taken into account by implementing the crop water need (agricultural water demand) and precipitation as dynamic input data such that in the end due to balancing all data, e.g. irrigation, evapotranspiration, etc, become time

The first task in setting up models covering the water resources of an area of this size is to construct a water budget. The water budget is a theoretical device that supports struc‐ turing the water resource system and identifying the most important water fluxes. Here fluxes into and out of the system has to be collected as well as the water fluxes within the model area. The intension must be to realize the relation of water fluxes to each oth‐ er, to quantify them, separating the more important from negligible water fluxes and to estimate the error that happens due to neglecting them. Since most of the quantities in the water budget are not independent from each other, the quantification of the water budget must be an iterative process. Fig. 5 illustrates the water budget of the region of Beijing. All the before mentioned fluxes are entried. The width of the arrows corresponds

Since the groundwater model is spatially distributed the input data for the groundwater recharge and the exploitation have to be spatially distributed as well. The above men‐ tioned water budget can be regarded as a lumped parameter model for the whole region. The next step is to relate these data to locations by adapting the water balance with re‐

**•** An approach which is followed quite often is to regionalize by means of land use maps. The land use of the considered region is depicted in Fig. 6 showing eleven land use classes. These classes can be summed up to the following four classes:urban and

**2.** In a second step the budget data are regionalized by means of land use maps.

/a. The

Regionalization of the water budget means to adapt and evaluate the balance equation

$$P = GWR + ET + SWR\tag{5}$$

for each of these classes. It denotes *P* the precipitation rate, *GWR* is the groundwater re‐ charge, *ET* the evapotranspiration *SWR* corresponds to the surface water runoff. There are some quantities which are relevant for every class, like infiltration and there are some which are specific for a certain group. And for other classes additional quantities have to be added, i.e. irrigation rates (*IRR*) for agriculturally used areas.

ta for the groundwater model match the data for the surface water model, i.e. that at same

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Nevertheless, the user can be supported by a parameterization software, as it was realized within the Scenario Wizard of the Beijing DSS to ensure consistency as good as possible. With respect to the groundwater model the scenario is complete and consistent only if the

In order to obtain a complete and consistent set of input data for the groundwater model the user has to pass through the groundwater panel of the DSS Scenario Wizard and a so-called groundwater project is created. A groundwater project is a part of the scenario containing all

Within the GW panel the user has to execute five subpanels such that in the end at least a

**1.** The first subpanel calculates the surface water recharge. For this a weighting map is re‐ quired that determines how much precipitation becomes surface water in direct or indi‐ rect manner. On the other hand a reliable precipitation map for the entire model area is necessary. Since the precipitation is not constant over the year we also need temporal weights that define the temporal distribution of the precipitation rate. The Scenario wiz‐ ard provides a number of precipitation maps of the past which can be also used for fu‐ ture scenarios. The surface water recharge is not a direct input data for the groundwater model but it is required to determine the distribution of exploitation and groundwater

**2.** In the second step the agricultural irrigation from groundwater is and the total spatially distributed exploitation from groundwater is derived. For these calculations a map of the agricultural used areas (irrigated areas) is needed as well as corresponding informa‐ tion about the crop water need/ agricultural water demand. In addition some informa‐ tion about the irrigation from surface water and waste water are requested. Since the agricultural water demand is not constant during the year a temporal distribution is

**3.** In the third subpanel the minimal surface water inflow and the diffuse losses in urban areas is computed and therefore maps of water areas and urban areas are requested. The resulting information is incorporated into the calculation of the groundwater re‐

**4.** In this subpanel all input data with respect to the well fields and the inflow parame‐ ters have to be defined and entered in to table which asks for yearly data of the ex‐

time periods in same regions the same precipitation rates are considered.

before mentioned data are available for the complete simulation horizon:

complete set of input data for the groundwater model is generated.

charge from surface water areas and from urban areas.

**•** Boundary conditions (well fields and inflow)

**•** Spatially distributed groundwater recharge

**•** Spatially distributed exploitation

recharge in time and space.

needed as well.

groundwater relevant data.

**•** Initial conditions

**Figure 6.** Landuse map of the region of Beijing
