The Monterey County Water Resources Agency (MCWRA) has combined Global Positioning System (GPS), Geographic Information System(GIS), and Relational Data Base Management Systems (RDBMS) for the purpose of tracking and managing the water resources of Monterey County. This paper will give a non-technical review of the history of this development effort. The lessons learned along the way will be emphasized for the benefit of those who are interested in, or are currently involved in, similar development efforts.
The principle industry within the Salinas Valley basin is agricultural production. As of 1993, agriculture represents a 2.2 billion dollar per year industry. An estimated 85% of water used in the Salinas Valley is used is by agriculture. The population of the valley has been growing and its water demands for urban use have been increasing.
The area has been experiencing overdraft on the order 50,000 acre feet per year and is experiencing seawater intrusion which underlies approximately 16,000 acres of land along the coast. This condition has been greatly worsened as the result of a 6-year drought. Nitrate contamination of the aquifers is also occurring through the valley.
The decline of water quality and increased competition for available supplies has caused the Agency to become much more aggressive in its management of the resources. After studying the agency's data management needs, it became clear that the only efficient way to store, manage and disseminate the vast amounts of data involved would be through the use of GIS and RDBMS technology.
Much of the data had never been accurately georeferenced, and since the data needed to be able to support a wide range of map scales, GPS technology became the obvious cost-effective choice for determining the location of data sites. Water wells are the key source of hydrologic, water quality, and geologic data pertinent to groundwater. These became the first objective for field location.
The Agency chose to purchase GPS systems that would allow the data to be collected as GIS features along with each feature's associated attribute information. The Agency currently uses Trimble Pathfinder Professional software and Geolink software, both of which can directly export data into a variety of GIS formats. Both software systems utilize the Trimble Pathfinder receiver for collecting field data (Rover data). There are advantages and disadvantages to each software suite. However, these differences serve to enhance the end result rather than diminish it. Geolink's data collection scheme allows for a more flexible attribute database creation. It is also easier to master by personnel who don't normally work in the field. Its major limitation is the portable computer on which it runs. The hardware industry has only recently produced a waterproof, dustproof, shockproof laptop or notebook computer with an 8- hour battery. The Trimble Pathfinder Professional system, although its database is more awkward to set up, utilizes an extremely sturdy data collector that will stand up to very harsh environmental conditions. It also has far superior data correction, editing and display capabilities.
It was decided that all of the GPS data would be differentially corrected. This meant a base station would be required. Initially, this need was met by renting the use of a base station from a local surveying firm who specialized in GPS survey. After the first year of GPS data collection, the Agency staff found it more cost effective to purchase its own base station receiver. Ideally, the GIS that will be receiving all this data should be in place with its attribute tables clearly defined and tested before the GPS database that supports it is developed. In the Agency's case, financial considerations meant that priorities had to be assigned to the order of events. Data collection was given first priority. In order to circumvent any unanticipated problems or needs, it was decided create a GPS database that includes any and all possible information about a well that could be gathered in the field. Emphasis was placed on items that could possibly be cross-referenced to other databases (i.e., State well numbers, P.G.& E. plant and meter numbers...etc.) at a later date. Additionally, attribute values were collected that would be specific to each individual well, like pump and motor configurations and other hardware. The tools available within the database itself would be used to select and separate the information into functional arrangements.
SAGIS, which is comprised of ArcInfo GIS software. SAGIS makes extensive of Arc Macro Language (AML) to create graphic user interfaces, automate data processing and analyses.SABRINA (Santa Ana Basin Relational Information Network Application). SABRINA was constructed using Oracle Relational Database Management System. SABRINA stores and manages time series data on point locations, referred to as "Stations", where water quality and/or water quantity information is gathered.
SAGIS uses ArcInfo's Database Integrator to move data back and forth between SAGIS and SABRINA. Queries to SABRINA are handled through Structured Query Language (SQL) calls.
Since it was determined that SAGIS would satisfy approximately 75% of the Agency's short-term anticipated needs, the benefit of entering into a users group agreement and adopting the SAGIS application was immediately obvious. For the sake of clarity, the name SAGIS was changed to WRAGIS (WATER Resources Agency Geographic Information System) and the name SABRINA was changed to MOCRINA (Monterey County Relational Information Network Application)for the Agency's system. By agreement, any and all other changes to the applications can only be made with consent from the users group committee. This allows the application developers to better provide continued support throughout the entire users group and allows for better implementation of planned upgrades.
There are individual cases when local conditions at a well site have caused degradation of coordinate accuracy. Almost all of these errors can be attributed to:
These two phenomena cannot be eliminated be differential correction. Nor can the operating parameters of the rover receivers be set to filter them out. Fortunately, properly trained field personnel can easily recognize the situations when these phenomena are likely to occur and take the appropriate measures to minimize their effects prior to actual data collection.
For each day of field work, a list of wells within a given "Target Area" was assembled and the wells were plotted as accurately as possible onto base maps. For the reasons stated above, these maps were often times only a rough estimate of actual locations and were intended only to place the field person in the right neighborhood to began searching. Lists of known information that might assist in identifying the selected wells were compiled and sent along with the maps. Although not always current or accurate, these maps and information would at the very least allow the field person to verify that they are at the wrong well or that the well in question has probably been destroyed.
It is worth mentioning that books listing geographic place names have proven to be invaluable during pre-mission planning. The written description of a well's location was often referenced to a landmark. As years go by, landmarks tend to become forgotten or their names change. Without a method to correct for this, these references were of little use. Fortunately, a book of current and historical place names for Monterey County was published about the same time that this work began. The information provided in that book made it possible to locate some wells that had previously been determined unrecoverable.
During the data collection process, it has been found that the field personnel may encounter people that want explanations concerning the work being performed. The attitudes, motivations and cultural backgrounds of these people can be quite varied. Its has proven useful to spend some time preparing a couple of explanations of differing levels of complexity ahead of time and practicing these along with good public relations skills, to prevent these situations from deteriorating into an unworkable condition. If the receiver can be set up quickly enough, these efforts can at the very least create a stalling action to allow the receiver to collect as much data as possible during a potential confrontation.
After collecting the well data, the field person can close the point feature and then open a line feature to record the path back to the public road. To do this, the field person fixes the GPS antenna to a magnetic mount and place the antenna on the roof of his vehicle. The attribute table for this road should match whatever roads coverage is being used by the GIS. In this way a record of access to the well in question can be recorded for a minimal addition of labor.
The differential correction process is automated and handled entirely by the computer. In the event of an error during this process, the computer will provide the user with an error message that usually describes how to correct the problem.
Viewing and editing the corrected data can usually be performed in a graphic environment. It mostly consists of deleting stray positions that cannot be differentially corrected. A good example of this would be Multipathing. These positions are usually readily identifiable and easy to remove. Attribute data is also checked and corrected where needed. It is important to do this editing as soon as possible after the data collection is performed. The chance for error becomes greater if the field person's memory's are allowed to become cluttered by a succession of days visiting numerous wells. This also implies that the field person must be part of the entire development effort. This is one of the most productive methods found to let the field crew become personally invested in their own performance.
As mentioned above, the roads coverage and other coverages depicting man-made features need to be enhanced. Although it might not be feasible for the Agency to accomplish this independently, preference will be shown to data sets collected using GPS technology.
The agency contracted with a private firm to fly an intensive aerial photo survey of the Salinas Valley basin. The delivered products of this survey included a digital orthophoto of the basin, a digital elevation model of the entire basin capable of supporting a 10-foot contour; for two project areas within the basin DEM's capable of supporting 5-foot contours, a 1:12,000 scale roads center line and parcels coverages. Because the firm which was awarded this contract utilizes onboard aerial GPS, only a third as many ground control point needed to be established. These points cost approximately $1,000 each to place. Considering that the flight plan had to encompass about 300,000 acres, this represents a huge monetary savings to the Agency. To further protect its investment the Agency's own base station has been utilized as a backup to the survey grade receiver used for this project.
The agency currently has one base station receiver and three rover receivers. Formalized training and standardized data collection manuals have been created at this time. Field personnel have been given a week-long introductory course to GPS technology. This is followed up with additional training specific to the projects they are supporting. More training and data collection procedures will be created as additional projects are developed.