Zhou Xiaoyuan¹, Zhang Yongbo¹, Huo Zhibin¹, Wang Shiqin²

1. Institute of Hydrogeology and Environmental Geology, CAGS, Shijiazhuang, 050061

2. China University of Geosicences, Beijing, 100083

^* Project support: Nationwide land and resources investigation project "All-China Groundwater Resource and Its Environment Problems Investigation and Assessment" (200310400034)

First author: Zhou Xiaoyuan (1975-), male, assistant researcher, engaged in the study on informationism construction in the field of hydrogeology, engineering geology and environmental geology.

Abstract: With an end of web application in the process of groundwater resource dynamic state assessment in view, the groundwater resource dynamic state assessment mechanism and realization process have been studied in focus. And through the development of groundwater resource dynamic state in the North China, the principle of dynamic state, process and key technical measures have been expounded.

Key words: groundwater, dynamic state, resources, WEB, service, source and sink item

In China, groundwater is important water resource and basis and condition of the sustainable development, and also the core of environmental and development; Especially in the arid, semi-arid regions where are short of surface water resource, groundwater plays an very important role. The groundwater resource assessment is much concerned by the governments of various levels. To understand the distribution and dynamic change of groundwater resource in a certain area is of important significance for the industrial and agricultural production and economic construction.

In the past, the groundwater resource assessment was conducted through analyzing groundwater exploitation status, exploitation scheme and various factors in the process of exploitation, constructing the regional groundwater numerical model, and afterwards including the data supplement, data gathering, parameter adjustment and model verification, then the final results were obtained. However, a few year or more passed since the initial data gathering, the groundwater resource information can not be checked in time and even more there is no way to make clear of the dynamic change of groundwater resource in recent a few years or recent a few months.

With the rapid development of national economy in China, the demand for water resources is more and more pressing. No matter to make the national planning or to arrange the production on the regional scale, it is an important thing to make clear of the latest status of groundwater resource in the area. If the groundwater resource status is not clear, it is possible to cause the random exploitation of groundwater resource (the groundwater resource is exploitation according to the earlier exploitation planning when the great change of groundwater resource occur) or exploitation of groundwater resource (exploitation velocity is bigger than the recharge velocity), which will bring the huge loss to the national economy and future generations.

Considering that the current information technique provides strong data processing capability and network working, so the real time exploitation data adjustment model parameters and verification exploitation scheme can be got so as to realize the prompt use, distribution renewal of groundwater resource information and make the real time groundwater resource dynamic assessment. In the paper, the groundwater resource in the North China has been taken as an example with the purpose of realizing the groundwater resource dynamic assessment to study the mechanism and realization process of groundwater resource dynamic assessment.

Fig.1 Dynamic data based groundwater resource assessment model Diagram

1 Dynamic Data-based Groundwater Resource Numerical Calculation Model

1.1 Introduction to groundwater resource quantity numerical calculation model

At present the commonly-used groundwater assessment procedure software covers the finite unit based FEFLOW, FEMWATER/LEWASTE and Finite-difference based PWWIN, Modflow, GMS (includes Modflow calculation modulus). Among them, the Modflow is used most frequently in the global scale. Even for the visualized groundwater flow assessment software PMWIN and GMS. Its core of internal calculation modulus is Modflow software. The Modflow, the short form of Modular Three-dimensional Finite-difference Groundwater Flow Model, was developed in 1980s by McDonald and Harbaugh from the U.S. Geological Survey with the Fotran language. It is a numerical simulation software for groundwater flow in the pore medium. Because the Modflow can directly solve most problems in groundwater simulation without needing to verify the source procedure, so it provides relative standardization software and also brings much convenience for the academic exchanges, thus, since the development of this software, the Modflow has been widely used in the fields of scientific research, industrial and agricultural production, environmental protection, rural and urban development planning, water resources utilization. So far it has become popular software for the groundwater movement numerical simulation. Because the Modflow adopts the finite-difference method, independent modulus designing, with the feature of simple principle, clear structure and fixed format of data input, therefore, it can provide the realization possibility for model software data connection.

In the paper, the study on network data dynamic obtaining technique and Modflow establishing modulus technique and the setup of dynamic groundwater resource assessment model have been emphasized.

1.2  Dynamic data based groundwater value calculation model

The Modflow based groundwater resource assessment model initially is the "static state" model operating in the single computer. In order to accord with the operation mode of dynamic data, the groundwater resource assessment model has been improved to become a "dynamic-static" model as shown in Fig. 1.

The "static state" in the "dynamic static" groundwater numerical calculation model means the quantity that there is no much change in the short period in the study area, such as geological structure, regional boundary conditions, basic parameters of the model (here it means the verified parameters including permeability coefficient, water yield and water release coefficient), mathematic calculation of the model (the parameters verified true and reliable) and output file format (which is easy to extract infiltration in the results display), namely, the data file required by the model has been determined: DIS.LEF, PCG and OC files.

The "dynamic state" in the "dynamic static " groundwater numerical calculation model means the parameters can be renewed dynamically of the numerical calculation model, such as recharge, runoff, discharge conditions of groundwater in the study area, which are called as source items. The main source items covers: Precipitation infiltration recharge, irrigation infiltration recharge, river leakage recharge, lateral runoff recharge, the main sink covers evaporation, exploitation for the industrial and agricultural use and household use, lateral runoff discharge and river channel discharge.

In the "dynamic-static" groundwater numerical calculation model, in addition to the source items are in dynamic state, other two aspects are also included: one is the dynamic processing for the simulation period, which can be used for one year or longer simulation or prediction calculation, another is the dynamic processing of source items, which stores more than one copies of source items data. The simulation starting time and prediction calculation time have been determined according to the year for the simulation period and the relative source items in the database have been used to make assessment calculation or prediction calculation to get the water level information after the simulation period.

2 Groundwater Resource Dynamic Assessment Mechanism

2.1 Web service and dynamic data gathering technique

The Web service is the function integration that seals some individual entities and distributes them to the network to be used by other procedure and it is a new method used through the HTTP operating the long-range method. It working principle is to expose one or more applied API and dispose them as Web service. Trough a series of standard, agreement visits unrelated to the platform, any user on the net can use these service freely and in the form transplatform. Just because of the transplatform loose coupling features, the Web service has the great vitality. And at same time it ensures the dynamic linking and management of various application procedure.

The basic agreement can be used from the Web service including SOAP, WSDL, The SOAP (Simple Object Access Protocol) technique is based on the XML standard, which describes in detail how to use the Web service through the HTTP, the long-distance SOAP server can understand the operation order and perform all the work, such as object example, operation of order and response to the client in SOAP form. The Web service also can use the WSDL (Web Services Description Language) to describe and inquire the Web services during the operation state. The WSDL uses XML to provide the description in all methods and the description in a method needed by the order.

The feature of Web service is to obtain the data on the network on behalf of the network terminal clients' requirements, with an end that to simplify the client operation and the basic protocol of Web service can pass the network firewall, thus, the Web service is usually used to restrain the sharing of private data within the firewall to the public. With the Web service to share the internal data within the firewall, not only the data can be protected effectively and safely, but also the safe management to the data can be realized through the management of Web service. This provides the data protection and management coordination mechanism for the data sharing.

The dynamic data obtaining technique means to get the needed dynamic data from the network with a certain technical means. The dynamic obtaining is characteristic of two aspects: On one hand, according to the different requirement, the needed data will be dynamically checked, and will be got on request and on use, other than all data will be searched in all database for each requirements. On the other, the data for each requirement are different and dynamic and renewed with time. The renewal of data leads to the dynamic change of application result and this is very evident in the process of groundwater resource assessment.

Fig.2 Groundwater resource assessment dynamic data gathering process diagram

To realize the dynamic data obtaining through the Web service, the advantages are not remarkable in the regional network. Because in the regional network, the data and clients are all protected by the firewall, so the efficiency of obtaining data through the Web service is no better than that directly adopting the data engine. However, in the distributed extensive network or internet, the network terminal client is hindered by the firewall with the data, and the database engine technique can be used directly, so in this case the Web service can be used and with a certain data connects the long-range multiple distribution database can be controlled just like controlling the local database.

As shown in Fig.2, Knot 1, Knot 2.....Knot N source items database can be reached through the Web service, and the data needed by model operation for groundwater resource numerical calculation model. Because each knot can be managed autonomously, the knot administrator can add the new data at any time such as groundwater recharge and discharge to the database. This just is the basic mechanism of realizing the groundwater resource dynamic assessment.

The dynamic data obtaining process for the groundwater resource assessment can be divided into three steps: one is the source items data service of single knot, during which the enquiry and extraction of source item data of each data knot will be conducted. Then is the dynamic extraction service of multiple knot based source item data, during which the dynamic extraction of multiple knot source item data will be conducted and the data will be summarized into the data file needed by the groundwater numerical calculation model. At last the groundwater resource numerical calculation model will be operated to get the operation results of the model.

Because of the Web service based groundwater dynamic resource assessment, the corresponding technique measures should be taken in the light of Web application system characteristics during application and development of above-mentioned three steps, for example, asynchronous service adjustment technique will be used to realize the adjustment and utilization of each knot service and processing in the groundwater resource numerical calculation process.

2.2 Realization of dynamic data of the North China groundwater resource model

Based on the recharge, runoff and discharge in the North China, the following items database has been established as follows:

Table 1 Each item database in the North China

The spatial parameters of groundwater resource numerical model mainly in the GIS form represent the spatial distribution of groundwater resource model parameters, while the numerical data table of groundwater resource numerical model records a great number of dynamic data in the form of outer attached attribute table. No matter the structure and expression pattern of database of each knot are same or not, however, after the seal and extraction of data through the knot, all the dynamic data needed for the model can be obtained.

Fig. 2 shows the data dynamic extraction service of groundwater resource numerical calculation model as following functions:

(1)  Each knot will be dissected into grids by application of web service of Mapgis, IMS, to form point, line and plane files of M row and N column;

(2)  Each model spatial parameters of each knot impose with the point, line and plane files of the grid to make the spatial analysis;

(3)  Spatial parameter data of each knot and numerical data table are sealed in combination and then the each numerical value of each grid unit can be obtained;

(4)  To merge the numerical values of multiple knot grid unit;

(5)  All the grid numerical values of the whole model study area output to data file of groundwater resource numerical model.

3 Realization of Dynamic Assessment System of Groundwater Resource in the North China

The basic flow chart of dynamic assessment system in the North China is shown as Fig. 3.

Fig. 3 Flow chart of the North China groundwater resource dynamic assessment system

The North China groundwater resource dynamic assessment system is realized by the Web service plus Web application procedure and the system adopts the Web application system and Web service, developed by the Microsoft Visual Studio.NET 2003. In the system the groundwater resource numerical model is interpreted into EXE. file by Fortran 77 and finally sealed to the Web service by the Microsoft Visual Studio.NET 2003; The system can be visited directly through the internet and the latest groundwater resource exploitation and recharge can be got through checking the data service distributed in Beijing, Tianjin, Shandong, Hebei and Henan. The groundwater numerical calculation model is used to get the North China groundwater resource dynamic assessment results in combination with other model parameters.

The North China groundwater resource dynamic assessment system is the Web based application system, and processes the groundwater resource dynamic assessment results with the help of software and hardware of the servers. In the study, software such as Surfer and Mapgis have been disposed on the server terminal, through the Web service, the isopleth zonation map of assessment results can be formed on the server terminal as shown in Fig.4.

Fig. 4 Assessment results of groundwater resource dynamic assessment in the North China by Web system

4 Conclusion

The web based groundwater resource dynamic assessment mechanism can solve the problems such as data dispersion, data protection lacking, data unshared, data lacking for model parameter adjustment in the process of groundwater resource assessment. Moreover, in combination with groundwater resource numerical assessment model, it can establish groundwater resource dynamic assessment system, through which, one can issue the real time, dynamic change information of groundwater resource.