THE HYDROLOGIC CYCLE
Water is continually on the move on earth and within the earth’s atmosphere. It connects everything and all life depends on it. It exists as a solid (ice), liquid, and gas (water vapor). It is present in the air, on land, beneath the land surface, and in the seas. It not only varies spatially in its quality and quantity, but also temporally; some deep ground waters are thousands of years old.
In describing the hydrologic cycle or the movement of water on earth, one can choose to start anywhere in the cycle. As water vapor is transported through the atmosphere by winds and air currents, it cools, condenses and falls to earth as precipitation. This can be as rain, ice, sleet, or snow. This precipitation may then be intercepted and taken up by plants, infiltrate into soils, or flow over the surface into streams, rivers, lakes, and oceans. Water on the surface returns into the atmosphere via evaporation. It can also return to the atmosphere via evapotranspiration through plants. Water infiltrating soils may continue downward movement to saturated zones in the subsurface, where it becomes ground water.
GROUNDWATER-SURFACE WATER INTERACTIONS
The top of ground water is called the water table and its location relative to the ground surface can change depending on geology, precipitation events, and well pumping. Ground water can be connected directly to surface water such as lakes, wetlands, streams and rivers. Water can move from ground water to surface water (e.g. gaining streams) or from surface water into ground water (e.g. losing streams). This can be reversed at the same location of the ground water – surface water interface (GSI) depending on precipitation and other water inputs (e.g. release of water from reservoirs) or withdrawls (e.g. well pumping). Therefore, to focus solely on surface water behavior for water quantity and quality management can be a fatal flaw in any water resource management effort.
Some interesting facts about water
- Only 3% of the earth’s water is fresh water, that is of drinking water quality
- 97% of the water on earth is salt water
- 69% of the fresh water is trapped in glaciers leaving only 1% of the total fresh water as available
- 30% of all fresh water is ground water and the main source of drinking water for people living in rural areas.
Ground water is often taken for granted because of “out of sight-out of mind mentality”. Groundwater accounts for approximately 50 percent of the total reported water use in the state of Oklahoma; surface water accounts for the remaining 50 percent (State of Oklahoma, Groundwater Monitoring and Assessment Program, 2012, OWRB White Paper). Understanding the connections between ground water and surface water as part of the hydrologic cycle is crucial to successfully managing our states’ water resources. Increasing demands for sources of water, combined with changing land use, population growth, aging infrastructure, and climate change, poses significant threats to our water resources. Failure to manage our state’ waters in an integrated, sustainable manner will limit economic prosperity and jeopardize both human and aquatic ecosystem health.
THE HYPORHEIC ZONE
Ground water – surface water interactions (GSI) are integral to the management of our ground water and surface water resources. It is at this interface where sharp variations in oxygen levels, microbial processes, and sediment-water chemical reactions occur. This zone is called the hyporheic zone. It is an important source of nutrient uptake via microbial processes, and adsorption-precipitation reactions controlling metals, nutrient and organic compound transport. A proper understanding of the hydrologic system must look at the entire unit of surface water and adjoining ground water and in particular, the hyporheic zone. Use of stream gauges alone cannot give us an accurate picture of surface water quantity and variations or trends in that resource in terms of both quantity and quality. Ground water monitoring wells are also needed and can be used to monitor water quantity and quality over time in our major aquifers. The addition of more real-time monitoring wells to the few that currently exist in Oklahoma will provide a complete picture of our water resource quantity and quality.
from USGS Circular 1139
Ground water monitoring can provide information on short-term and long-term changes in groundwater recharge, aquifer storage, and climate variability impacts. A fully developed and integrated ground water monitoring program can assist with management decisions on regional interstate and regional intrastate effects of ground-water usage, availability, trends, and quality. These wells would also provide valuable information on interactions between ground water and surface water and provide the basis for more accurate ground-water flow and contaminant transport modeling at local and sub-regional scales.
According to recent surveys by the National Ground Water Association, the Ground Water Protection Council and others and summarized in “A National Framework for Ground-Water Monitoring in the United States” (2009), Oklahoma has a statewide ground-water level monitoring program but there are only a few wells that provide continuous monitoring data. As far as a ground water quality network, the surveys indicate that it is inactive in Oklahoma. Sixty-seven aquifers and aquifer systems have been identified by the USGS as principal aquifers in the U.S. (USGS, 2003, Principal Aquifers of the United States, prepared by the USGS for The National Atlas, scale 1:5,000,000). All or parts of eight of those sixty-seven are in Oklahoma, including the High Plains, Rush Springs, Central Oklahoma, Ada-Vamoosa, Ozark Plateau, Blaine, Arbuckle-Simpson, and Edwards-Trinity aquifers. As of April 2012, the OWRB in cooperation with the Oklahoma Mesonet (http://www.mesonet.org/index.php/weather/groundwater/) has continuous real-time records for five wells. The Oklahoma City USGS Water Science Center has fifteen operating continuous real-time monitoring wells (http://waterdata.usgs.gov/ok/nwis/current/?type=gw&group_key=county_cd).
Real-time continuous data appears to be completely absent for two of the eight aquifers in the state and three others only have one well.
The need for a state-wide ground-water monitoring network is profound. The lack of one limits our ability to adequately manage our states water resources. Impacts to ground water cannot be assessed in a timely manner without such a network. The 2012 Oklahoma Comprehensive Water Plan called attention to the fact that characterization of ground water quality and projected future available quantities was not possible due to the lack of long-term data and indicated that such data will only become more important with time in light of forecasts that suggest more reliance on ground water to satisfy state water needs. This same trend has been observed in many other parts of the country.
A strategic monitoring well network needs to be established for the state that is capable of real-time monitoring of water levels at a minimum. The network should be established to monitor water resource trends for all eight major bedrock aquifers and to provide real-time data on GSI for most of the eleven major alluvial aquifers. The 2012 Oklahoma Comprehensive Water Plan (OCWP) recommended ground water quality/quantity funding for 2012 at $815,000. In the state budget for 2013, the Oklahoma legislature and the Governor have adopted and funded many of the high priority recommendations in the OCWP including 1.5 million dollars for water monitoring. The OWRB is currently developing a statewide Groundwater Monitoring and Assessment Program. This will allow for the establishment of a basic network as described above and would be a model for other states in the region and the country.
A comprehensive ground water monitoring network is important for the following reasons:
- short and long-term changes in storage and recharge
- short and long-term impacts from climate variability
- regional intrastate and interstate effects from ground water withdrawls
- interactions between ground water and surface water
- ground water contaminant transport and resultant impacts to ground water and surface water bodies
OKLAHOMA WATER SURVEY WEB PORTAL
In addition to continuously monitored wells by OWRB/Mesonet and USGS, other entities in the state have monitoring well data. This includes both water level and water quality data; however there is no central repository for the data or public access. A publically accessible web portal is proposed for the Oklahoma Water Survey. This would provide a central location for water resource information throughout the state for use by the public and water resource managers. With population increase, land use changes and climate variability there is an increasing need for fresh water, and ground water use is increasing. Based on water levels observed in a few wells, storage in some aquifers appears to be decreasing, but additional data collection along with better estimates of use and available supply are needed to determine changes in storage. Increased use of computer systems by municipal, state and federal agencies now make it possible to realistically attempt better coordination of data from multiple sources and platforms so that trends in water supply and water quality can be observed and not just inferred.