Compile and Characterize Existing Water-Resources Data

By first compiling hydrologic data to characterize the quantity and quality of their water resources, a Tribal Government will be able to best decide how to manage those resources. The following are some of the primary online sources of hydrologic data in Oklahoma.

Descriptions of common types of groundwater, surface-water, and water-quality data are as follows.

Groundwater Levels—The term “groundwater level” refers to the depth from the land surface to the top of the water table; groundwater-level altitudes are calculated by subtracting the groundwater-level measurement from the land-surface altitude at the well referenced to a datum such as the North American Vertical Datum of 1988 (Cunningham and Schalk, 2011). Groundwater levels can be used to help assess the amount of groundwater in storage and general flow directions in an aquifer system. A typical continuous groundwater-level monitoring well in Oklahoma can be seen in figure 3.

Groundwater levels in alluvial aquifer systems are usually less than those in bedrock aquifer systems because alluvial aquifer systems are contained in relatively shallow alluvial deposits (Hoekstra and others, 2011). Groundwater levels in bedrock aquifer systems can vary considerably and can be shallow or deep depending on the extent and consolidated nature of the rock.

Groundwater levels in Oklahoma (OWRB, 2021b) can be affected by seasonal fluctuations in the water budget, nearby persistent groundwater use, precipitation, and direct recharge from streams or surface inflow to the aquifer (Alley and others, 1999). Groundwater levels measured over time provide insights into how groundwater availability may fluctuate in a particular area. Groundwater generally flows from high head (higher altitude) to low head (lower altitude), and the general groundwater-flow direction can be interpreted from synoptic groundwater-level measurements in multiple wells completed in the same aquifer. Springflow discharging from the Arbuckle-Simpson aquifer is the source of water to Turner Falls, seen in figure 4.

Aquifer Characteristics—Aquifer thickness and storage properties, along with groundwater levels, can be used to assess groundwater storage. The amount of groundwater available in aquifers is calculated through measurements of groundwater levels and numerical groundwater-flow models. This information can be used to determine how water-usage patterns will affect groundwater availability in the aquifer in the future (Winter and others, 1998). The two types of aquifer systems in Oklahoma are bedrock and alluvial. Bedrock aquifers are composed of consolidated material such as limestone, dolomite, sandstone, siltstone, shale, or fractured crystalline rock (Hinaman, 2005). Alluvial aquifers are made up of unconsolidated stream sediments that typically allow water to move much faster than water can move in most bedrock aquifers. Characterizing the type of aquifer in a particular area can improve the understanding of groundwater storage and groundwater availability.

Streamflow—Historical and existing streamflow data (Ries and others, 2017; OWRB, 2021a; USGS, 2021) for streams in the jurisdictional areas of Tribal Governments and surrounding hydrologic drainage areas (watersheds) are often considered when creating a water plan. These data are usually collected in collaboration with Federal and State agencies. A typical real-time streamgage in northeastern Oklahoma can be seen in figure 5.

Reservoir Storage—Most reservoirs in Oklahoma were either constructed or are currently managed by the Bureau of Reclamation, the U.S. Army Corps of Engineers, or the Grand River Dam Authority. Additional reservoirs are owned and operated by various State and Federal agencies, cities, and other entities (Johnson, 2021). Reservoir storage and release data for many reservoirs are accessible from the reservoir and dam websites previously listed.

Springs—Springs are discharge points where groundwater flows onto the land surface. Springs can be ephemeral or perennial, depending on changes in groundwater levels and groundwater flow, and the amount a spring discharges can change over time as a result of changes in the groundwater budget. Measurements of spring discharge throughout the year can provide insights into how the groundwater budget changes as a result of variations in seasonal groundwater discharge to streams and reservoirs.

Water Quality—Data that describe the quality of water are important in determining the ways that the water can be used. To be considered potable, treated drinking water needs to meet the National Primary Drinking Water Regulations for constituent concentrations developed by the U.S. Environmental Protection Agency (2009). Water used for irrigation can be non-potable (National Blue Ribbon Commission for Onsite Non-Potable Water Systems, 2017). Monitoring the quality of the water resources during runoff events can provide insights into the relation between land use and water quality. For example, runoff from urban or agricultural land uses can lead to excess amounts of nutrients, such as phosphorous and nitrogen, entering the water (Paizis and Trevisan, 2021).

Denitrification is a natural process that occurs in aquifers to reduce nitrate and nitrite concentrations in groundwater through microbial processes to produce gaseous forms of nitrogen (Blicher-Mathiesen and others, 1998). Nitrogen exists naturally in the environment but is also introduced into groundwater resources through nitrates in runoff from fertilized land and livestock farms, atmospheric nitrates from combustion of fossil fuels in rainwater, residual nitrogen in sewage effluent, and natural oxidation processes (USGS, 1999). The gaseous forms of nitrogen are released from the aquifer in the form of nitrogen gas bubbles, as seen in figure 6 (Christenson and others, 2009). In figure 6, denitrification can be seen taking place in the Arbuckle-Simpson aquifer.

Water Budget—A water budget accounts for the inflows and outflows of surface water and groundwater in each watershed during a specified period. A water budget is prepared from a collection of hydrologic data consisting of sources of water, water use, and land use that will be used to evaluate the spatial distribution of water on Tribal lands. Calculation of a water budget for a water resource or specific area can inform Tribes on the amount of water available for use. Water budgets can be prepared for surface water, groundwater, or both by using real-time and long-term collected hydrologic data. Streamflow data can be used to assess the surface-water budget (the balance of stream inflows minus outflows on an annual mean basis). The surface-water budget can provide an estimate of the average amount of surface water flowing through a given Tribal jurisdictional area and changes in streamflow volumes over time. This type of assessment is normally done by using data obtained at continuous streamgages. Groundwater-flow models are typically used to assess groundwater budgets and can be used to assess changes to overlying streamflow and reservoir budgets; see Ellis (2018) and Smith and others (2021) for examples. Water budgets can change over time and are affected by changes in precipitation, water use, and land use. Once a water budget is calculated for a given period, projected future variability in the water budget caused by changes in precipitation, water use, or land use can be estimated. The results of projected future analyses of water budgets can facilitate the development of water plans by Tribal Governments.

Land Use—Land-use type can directly or indirectly affect surface- and groundwater quality and groundwater recharge. For example, the effects of urban, agricultural, and recreational land uses on water resources are appreciable and different. Urbanization and agriculture can affect soil porosity, which is the amount of space available between soil particles, altering the direction of runoff and affecting recharge rates (Reilly and others, 2008). Quarries and other mining activities can also alter the direction of runoff, affect recharge rates, and introduce contaminants to the surface water and groundwater (Langer, 2001). Extensive groundwater withdrawals to supply urban areas or to be used for agricultural practices or irrigation can cause groundwater levels to decrease appreciably, resulting in decreased water availability and impaired water quality (Bartolino and Cunningham, 2003).

Habitat—Streams and lakes and the riparian vegetation provide habitat for aquatic and terrestrial species. Riparian habitats can be negatively affected by degraded water quality and a loss of general riparian health, including habitat fragmentation. For example, land-use changes such as the removal of tree canopies along streams can degrade and fragment stream habitats (Yirigui and others, 2019). Riparian vegetation can also die or become unhealthy if base flows are diminished by excessive groundwater withdrawals, resulting in stream erosion and sedimentation issues (Stromberg and others, 1996). Without sufficient inflows of groundwater to sustain base flows, the water quality can become impaired. Biodiversity is dependent on abundant habitat and water availability and is affected by a loss in riparian health and degraded water quality (Montgomery, 1996). A healthy aquatic environment will sustain sensitive benthic invertebrate species referred to as water-quality indicator species; a loss of indicator species might mean the water quality has been impaired (Chambers and Messinger, 2001).

Establish Priorities and Identify and Fill Data Gaps

Once water resources have been quantified and described, and priorities have been established by the Tribe, then gaps in datasets can be identified and plans can be made to help fill those gaps. Water plans can incorporate planning steps and strategies to fill data gaps. Examples include planning to add a streamgage or make a series of streamflow measurements at a stream site that is crucial for quantifying outflow from a Tribal jurisdictional area. Additionally, groundwater monitoring equipment could be deployed at a network of wells to better understand groundwater resources and availability. Tribes with water-quality concerns could initiate water-quality sampling for nutrients such as nitrogen and phosphorus or heavy metals such as arsenic. If the concentrations of these constituents are elevated, drinking water viability, riparian habitats, and other water-resource concerns can be affected. Land use could also be evaluated to determine areas of excessive runoff. In these areas, the installation of storm retention ponds and green infrastructure (U.S. Environmental Protection Agency, 2015), such as rain barrels or green roofs where vegetation is planted over a waterproof layer, could be implemented to attenuate stormwater runoff and encourage sustainable water use.

Identify Problems or Concerns Related to Quantity, Quality, or Use of Water

Once water-resource priorities have been established and data have been collected, Tribal Governments are better enabled to identify potential problems or concerns regarding water resources. Continuously collected water-resources data can be used to discern trends in the data that could indicate problems. Possible problems or areas of concern could include aquifer depletion from overuse, decreased water quality caused by agricultural runoff and nutrient leaching, and habitat degradation. Numerous competing priorities for water resources make it challenging to balance sustainability with use.

Set Future Management Goals and Strategies

Effective long-term management strategies are designed to preserve the water resources for Tribal communities through adaptable water plans that can readily account for changes in land use and other types of landscape modification over time. Understanding the current water-resource uses and how they are changing is dependent on the availability of ongoing hydrologic data monitoring, including the collection of continuous (real-time) hydrologic data. Collecting different types of surface-water and groundwater data, as well as water-use and land-use data, can help to close data gaps in water plans and ensure the preservation of important water resources for the Tribes in Oklahoma.