DEVELOPMENT AND PRIMARY APPLICATION OF A GIS DATABASE FOR MIYUN RESERVOIR WATER QUALITY PROTECTION
ABSTRACT: A high quality database is the starting point for any GIS application. For Miyun Reservoir, a large amount of spatial data has been accumulated by numerous studies. This paper introduces a GIS database development in support of these studies. And some primary applications of the GIS database are also introduced.
KEY TERMS: GIS; Database; ArcInfo; Arcview; Miyun Reservoir; Water Quality.
2. DEVELOPMENT OF THE GIS DATABASE
3. THE PRIMARY APPLICATION OF THE GIS DATABASE FOR MIYUN RESERVOIR WATER QUALITY PROTECTION
1.1 Miyun Reservoir and Associated Studies
The Miyun Reservoir(Figure 1.1), built in 1960, is one of the most important reservoirs in the suburbs of Beijing, serving as the source of drinking water for the people of the capital. Situated in Miyun County 90km to the northeast of Beijing city, the Miyun Reservoir is the biggest reservoir in the Chaohe River-Baihe River water system. It has a total pondage of 4.375 billion m3 and a corresponding water surface area of 188km2. As industry and agriculture develop rapidly, the water supply in Beijing is getting in short . To ease up the problem of water supply for people's life, the municipal government of Beijing has decided to make Mivun Reservoir as a surface water source to supply water for the capital, thus the main function of the reservoir has turned from flood preventing to drinking water supplying, along with flood prevention and electricity generation. So the protection of the water quality of the Miyun Reservoir has become an important issue concerning the life and health of the people in the capital.
As the water quality of Miyun Reservoir has been the concerns of the public, several studies have been accomplished by different institutes , sponsored by different government agencies, such as Beijing Water Resources Bureau(BWRB), Beijing Environmental Protection Agency(BEPA), Beijing Waterworks Bureau, et al. . Many data have been accumulated through these projects, however, owe to the independent between these agencies and lack of the communication, many works are iterated.
In order to implement the share of the accumulated data, the development of a common database is needed.
1.2 Why GIS is adopted?
A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on Earth. GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps. These abilities distinguish GIS from other information systems and make it valuable to a wide range of public and private enterprises for explaining events, predicting outcomes, and planning strategies.
Spatial data are common in the reservoir water quality study, so GIS was identified as an important tool. The objective of this task is to develop a set of tools (models and GIS databases) that integrates the data from various tasks in this project and other projects to provide predictive capabilities with which the decision makers can evaluate the consequences of various water management options on the watershed of Miyun Reservoir.
2. DEVELOPMENT OF THE GIS DATABASE
2.1 Primary Data Collection
2.1.1 The basic data of Miyun Reservoir watershed
The basic data include the administration zoning, soil type, land-use, production value of agriculture and industry, natural resources, population, annual precipitation and so on. These data are related with pollutant sources, and thus have influence on the water quantity and quality in Miyun Reservoir. These data are collected from the yearbooks of the county in the watershed.
2.1.2 The reservoir operation and flow data
The reservoir operation and flow data (1988-1997) were provided by the Management Branch of Miyun Reservoir, BWRB. It is a series a MS Excel spreadsheet files. These data include the reservoir's inflow, outflow, water surface elevation and precipitation, along with other information.
2.1.3 The Reservoir historical water quality data
Since the construction of the reservoir, the water quality have been monitored by many organizations, including the Management Branch of Miyun Reservoir, BWRB; the Center for Environmental Monitoring, BEPA; and some institutes and colleges. For these data, the water quality data taken by the Management Branch of Miyun Reservoir, BWRB cover a long time series, but limited items; the data taken by the Center for Environmental Monitoring, BEPA has more items, but lack the data in the reservoir zone; the data taken by other institutes and colleges are only limited to specified time and specified items. These data are collected and organized in the database. The database contains 19 sample points data which was measured once a month during the period of 1988 to 1997. A total of 36 water quality variables is recorded, including temperature, DO, BOD5, and PH, etc. The location of each sample stations in the database was coded by an identification number.
ArcInfo was used in the initial analysis of the historical water quality status. The reservoir and its sample stations were digitized into ArcInfo coverages. Data of the selected variables were transferred to INFO files and the water quality measurements were illustrated by ARCPLOT map outputs.
2.1.4 The tributary and non-point sources loading data
A parallel project of non-point source loading assessment was conducted by the Center for Environmental Monitoring, BEPA. The objective of this project is to estimate the daily loading from the tributary watershed to the reservoir and to provide data to calibrate non-point source models used to assess future watershed land-use scenarios.
2.1.5 The point source discharge data
The point source discharge data were collected from various sources, including EPA's waste water discharge permit records and city/county waste water discharge monitoring data.
2.1.6 Cage fishery data
In Miyun Reservoir, there are about 1.35ha cage fishery. These cage fishery contribute a lots nutrients. The nutrients data from cage fishery are provided by a project which was conducted by the Center for Environmental Monitoring, Beijing Environmental Protection Agency(BEPA).
2.2 GIS Database Construction
2.2.1 Geographic reference system
The geographic reference system used in the GIS database of this study is the Beijing Coordinate System. The advantage of the system is that it is convenient for further manipulation when depth values (also in metric units) are involved, and convenient for share data with other projects.
2.2.2 Base map of the reservoir
Three sets of base maps are used in this study. The first is the 1:50000 Reservoir bottom elevation contour map(Figure 2.1). The second is the 1:95000 Miyun County map which contains the administration zoning, water system, land-use, road system, and so on(Figure 2.2, 2.3). The third is the 1:200000 topographic map of Miyun Reservoir's watershed(Figure 2.4). All these base maps are digitized using Mapinfo System, and then exported into ArcInfo system. Separate coverages are generated for different topographical features, sample station , point and non-point source loading.
2.2.3 Transformation of multi-source data
Data in various formats must be pre-processed before merging into the GIS database. The processing procedure can be summarized into the following steps (Figure 2.5) :
(1) Affixing location information. Data of sample stations are registered with the station location; data of point source discharge are registered with the discharge outlet location; data of non-point source loading are registered with the reservoir segmentation polygon which receives the loading; data of inflow and outflow are registered with the location where the flow is measured.
(2) Change into format of matrix records, so that each column contains one variable and each row represents one point or one polygon in the GIS coverage.
(3) Transfer into ASCII text file, so that it can be easily transmitted through computer networks and recognized by the ArcInfo System.
(4) Add data to INFO file. In ArcInfo, use the CREATE function to generate the corresponding INFO file for each ASCII data file, DEFINE the format of each variable in the file and ADD the values from the ASCII text file into the INFO file.
(5) Join with coverage. In ARC, use the JOINITEM function to attach the INFO data files with the corresponding coverage's PAT or AAT files.
3 THE PRIMARY APPLICATION OF THE GIS DATABASE FOR MIYUN RESERVOIR WATER QUALITY PROTECTION
3.1 Integration with GPS
Water quality monitoring is important in reservoir water quality management. However, it is difficult to identify the sample station's location in the open water. Using the GIS database and GPS receiver, it is easy to locate the sample station and relate the sample data with the GIS database.
Another use of GPS is in the investigation of pollutant sources and other information related to the management of the reservoir watershed.
3.2 View and Management of Data
The amount of data we collected are large and very specialized. It is very dull for decision maker to read these data , and also difficult to understand it. The GIS provide a powerful tools to map and analyze these data. This make it easier for decision maker to understand these data.
In Arcview, the attribute data(include water quality data, pollutants sources, and so on) are related with the geographical data, and then be viewed in the unique visualization form defined by users. Here are two example figures: Figure 3.1 illustrate the location of the water quality sample station and cage fishery in the Miyun Reservoir; Figure 3.2 is a map of Miyun Reservoir catchment which contains water system, the administration zoning( i.e. boundary of counties), and the calculated results of the population and labour force in each county.
3.3 Integration with WASP5 Model
3.3.1. Modeling Reservoir Water Quality by WASP5
In Miyun Reservoir, with the point and non-point pollution sources of poultry wastes, farmland fertilizers and top-layer soil erosion from the watershed, the oxygen, nitrogen and phosphorus levels become the focus of the water quality modeling. In this project, WASP5/EUTRO5 was used to model reservoir water quality.
The Water Quality Analysis program (WASP) was developed in l981 (Amborose, 1991) . WASP5, the updated version of WASP, is a dynamic compartment model designed to analyze a variety of water quality problems in ponds, streams, lakes, reservoirs, rivers, estuaries and coastal waters. Because of its unique flexibility, the model has been widely used to predict water quality responses to natural and man-made pollution.
The WASP5 modeling system consists of two stand-alone computer programs, DYNHYD5 and WASP5. The WASP5 program is supplied with two kinetic sub-models to simulate two of the major classes of water quality problems: EUTRO5 for conventional pollution and TOXI5 for toxic pollution. The details of the WASP5 was omitted here.
3.3.2 Integrating WASP5/EUTRO5 with ArcInfo
3.3.2.1 Generating Data Required by WASP5 through GIS Operations
(1) Topographical features
The topographical features of the reservoir are digitized into ArcInfo. According to the digitized contour , the topography of the reservoir bottom is generated by the CREATETIN function, which is a triangulated irregular network (TIN) model. It may be displayed by the VIEW function as a three dimensional model. Figure 3.3 is the Miyun Reservoir Bottom Elevation Model generated by CREATETIN.
(2) Segmentation of Miyun Reservoir
According to the use of the WASP5 model, the primary segmentation scheme of the Miyun Reservoir was made. All segment boundaries were defined in ARCEDIT environment. Background display of water quality information from sample stations, water flows, waste loading and reservoir bottom geometry data are options available for the user's selection, as references in the segmentation process. In this study, the segmentation scheme is illustrated using Figure 3.4. It includes 17 surface segments and 13 subsurface segments.
(3) Spatial measurements
Using the ArcInfo system, several spatial measurements are calculated:
(a) Surface distances. To construct the reservoir water quality isopleths, distances between each sample station and the Dams are required. Based on the sample station coverage, surface straight line distances are measured by the DISTANCE function in ARCEDIT.
(b) Surface and bottom areas. An ArcInfo coverage's PAT file provides the surface area of each segment polygon of the reservoir; the TIN operation generates bottom areas of the segments in a separate process, both are needed in the eutrophication modeling.
(c) Vertical profile areas. To model the flow and nutrient movement among the reservoir segments, the interaction area between each pair of segments is an important parameter. In ARCPLOT, the SURFACEPROFILE function can draw a profile graph over a surface according to each specified segment boundary arc, and write the surface profile coordinates to a specified INFO file. These data can be used to calculate the profile area.
(d) Average bottom slope. The SLOPE function calculation provided by ArcInfo generates the average bottom slope for each reservoir segment. The data are a parameter used in estimating the flow routing scheme of the reservoir and the exchange coefficients in different parts of the reservoir.
(e) Volume. Water volumes of the reservoir as a whole and of each model segment are calculated by the VOLUME function of ARCTIN. It is based on the reservoir bottom topographic features from the three dimensional model. Although still an estimation of volume, it is more accurate than the estimation by multiplying an average depth with the surface area. Moreover, it is convenient to recalculate the volumes given different water levels of the reservoir.
(f) Average depth. For each segment, the average depth is calculated by dividing segment volume by its surface area. The data are also required by the eutrophication model as input.
(4) Interpolation of sampled data
Due to various reasons, the number of sample stations in this study is much less than the number of segments in the simulation model. For the segments which do not have a sample station, nutrient concentration and other variables required by the model input must be interpolated from the known values of the sample data in nearby stations. The TINSPOT function of ARC can generate interpolated values for each specified point in the coverage. The operation is flexible in terms of interpolation calculation methods, segmentation schemes and sample variables .
3.3.2.2 Input-output cross-match between WASP5/EUTRO5 and ArcInfo
The input data cross-match from ArcInfo to WASP5/EUTRO5 is a complicated process. It includes the following steps (Figure 3.5) :
(1) Export from ArcInfo. Data for each segment, each interface boundary, or each sample point are first exported from ArcInfo files to ASCII text files.
(2) Merge with non-geographic data. There are other data needed by WASP5, which are not spatiai1y related, such as some function parameters or simulation control options. These data need to be merged with the ArcInfo exported data file;
(3) Re-format of the ASCII files. The ASCII data files have to be re-formatted to match the input format requirement of WASP5.
The output cross-match from WASP5 to ArcInfo is relatively simple. The basic processes are the same as the input cross-match. The processed files are converted to INFO files in the GIS database. AML interface programs select data of certain time and certain variables, defined by the user from the database, and relate them to the specified coverage for display, calibration or animation .
The applications of GIS techniques in environmental science are rare now in China, but it is believed that it has a good future. In this paper, the development of the GIS database for Miyun Reservoir water quality protection was described, This fundamental GIS database will support future projects on the water quality protection in Miyun Reservoir greatly. Some primary application of the GIS database were also presented. These applications described here include: Integration with GPS ,View and management of data and integration with WASP5 model. Due to time limitation, these applications are primary. The strategies for the water quality protection of Miyun Reservoir, supported by the GIS database, will be presented in the near future.
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¡¡
Haifeng Jia
PH.D Candidate, Engineer,¡¡
Dept. of Environmental Science
and Engineering
Tsinghua University
Beijing,100084
P.R.China
E-mail: jiahaifeng@hotmail.com
jiahaifeng@163.net
Yang Xiao
B.S. in Dept. of Environmental
Science and Engineering
Dept. of Computer Science
P.O.Box84-123
Tsinghua University
Beijing,100084
P.R.China
E-mail: gxy0903@hotmail.com
Shengtong Cheng
Professor,¡¡
Dept. of Environmental Science
and Engineering
Tsinghua University
Beijing,100084
P.R.China
E-mail: cst-den@mail.tsinghua.edu.cn
