Department of Defense (DoD) installations include environmentally sensitive wetlands generally referred to as vernal pools. These wetlands are known for their biological diversity and presence of rare and endangered plant and animal species. Managing these resources provide challenges within the framework of regulatory drivers associated with the U.S. Endangered Species Act and the U.S. Clean Water Act. Improved understanding of the hydrological functioning of these wetlands using innovative, yet well established, technologies can provide DoD and other federal agencies with important cost-effective tools to protect, manage, and monitor these wetland resources.

This project addressed the innovative use of existing technologies at three military installations. Demonstration sites included natural and restored vernal pools that encompass habitat for federal threatened and endangered species. The following technical objectives specifically addressed the issues covered in the demonstrations:

  • Demonstrate to DoD and other federal entities a cost-effective method of collecting higher quality hydrological data that can be used to measure hydrological functioning and performance in natural and restored vernal pools.
  • Demonstrate the use of non-destructive methods that accurately identify the surface topography and the depth and spatial extent of the subsurface water restricting layer for the purpose of evaluating the potential of sites and existing vernal pools for restoration as part of compensatory mitigation.

Demonstrate new quantitative methods to understand the relationships of both common and federally listed endemic vernal pool plant species to hydrology and soil moisture and identify them as hydrological indicators in order to establish realistic and predictable performance criteria for created or restored compensatory mitigation vernal pools.

Technology Description

Demonstrations at three DoD installations, including Beale Air Force Base (AFB), Travis AFB, and the Marine Corps Base at Camp Pendleton, identified four technologies that individually and together provide important new methods that have improved our understanding of vernal pool hydrology and the biological resources associated with them. The four technologies include: (1) real-time kinematic global positioning system (RTK GPS) capable of centimeter level topographic surveys; (2) ground-penetrating radar (GPR); (3) water-level dataloggers; and (5) soil moisture sensors and dataloggers.

The RTK GPS and GPR technologies provide data on the physical structure of vernal pool catchments, including the surface topography and soil subsurface water-restricting layers. The water-level and soil moisture dataloggers provide detailed hourly measurements of vernal pool hydrology. In combination, these technologies produce data sets that provide information needed to determine the potential for hydrological impacts to wetlands from DoD project activities by determining how the proximity of a project’s ground-disturbing activities might affect downslope vernal pools. The technologies provide important data for monitoring natural vernal pools, as well as ones restored or created for the purpose of compensatory mitigation. When compensatory mitigation is needed, the RTK GPS and GPR technologies provide data on the catchment structure and soil stratigraphy to identify site suitability for vernal pool restoration, enhancement, and creation. The demonstrations at each of the three military installations validated that the technical performance of these technologies represented improvements over existing methods in terms of usefulness, enhanced data benefit, the practicality of implementation, and cost benefit as determined by field data and participants in a demonstration workshop during the technology transfer phase of the project.

The benefits of these technologies and the data they provide are enhanced by the application of a water balance model that was used, calibrated, and validated during the demonstrations. This model provides a detailed and broader predictive evaluation of potential impacts from projects, predicts hydrological functioning of compensatory mitigation sites and wetland design, and facilitates predicting the possible effects of changes in climate.

Demonstration Results

The demonstrations at Beale AFB, Travis AFB, and MCB Camp Pendleton provided field testing of the technologies under different regional climates, geology and soils, and land management activities. Validation of specific performance objectives determined that the water-level dataloggers, soil moisture dataloggers, RTK GPS, and GPR all performed successfully as compared against specific success criteria. The validation data collected clearly showed that water-level dataloggers with hourly datalogging provided improved temporal and spatial data compared with the commonly used staff gauges and rulers that were only monitored three to six times during a wet season. The higher frequency datalogging revealed that the staff gauges underestimated the total period of water inundation or did not measure a dry down when no inundation occurred between rainfall events. The soil moisture dataloggers had not previously been used for any monitoring. They were found to be useful both for conditions when surface water inundation did not occur due to below average rainfall years or under dry soil conditions that first required the soil to be saturated. The soil moisture data were important for correlating with the presence and abundance of common, listed, and non-native plants.

The RTK GPS provided detailed location and more importantly elevation data relative to topographic maps and LiDar. The RTK GPS provided +/- 2 cm elevation accuracy, which could be correlated with water depth and days of inundation within a vernal pool and also with RTK GPS measurements of plant species presence within a vernal pool elevation gradient. In addition, the data could be used to develop detailed elevation models showing the placement of vernal pools within a catchment that could be used to identify whether a proposed project was up-gradient or down-gradient from a vernal pool. The RKT GPS measurements of vernal pools and their catchment also were important to determine the area of the upland that is contributing water inputs from upslope. Measurements using RTK GPS of created, mitigation vernal pools that were not hydrological success criteria often were found to lack sufficient catchment area to supply upland water inputs. This type of analysis could identify a potential impact to down-gradient vernal pools from proposed activities.

The GPR provided a non-destructive method to measure the soil profile for the presence, depth, and continuity of water-restricting soil horizons required to develop a seasonal water-table in vernal pools. This is a better method than the use of soil pits dug either by the auger, shovel, or back hoe. The GPR was able to collect data every three inches along transects and take depth measurements typically from the soil surface to three feet or deeper. The measurements covered 50 to 100 acres within one day and provided thousands of points of data relative to 10 to 30 soil pits in the same area. The GPR was used to identify the depth to water-restricting layers in natural vernal pools, evaluate sites for potential vernal pool creation or restoration as part of compensatory mitigation, and to evaluate existing created, mitigation vernal pools to identify the reason they were not functioning hydrologically. The collective use of the technology information can set a baseline for vernal pool hydrological functioning. However, extending the baseline hydrological functioning to annual variability in meteorological conditions, climate change, or changes in the landscape can be accomplished using a water balance model. A water balance model included in this report, and the Technology Transfer Manual provides one numerical, analytical method to make predictive calculations for hydrographs of vernal pools proposed for restoration, creation, or potential impacts to the landscape.

Currently, the three DoD installations, as well as private sector groups, have begun to use these technologies. In particular, the USACOE has included the use of water-level dataloggers in their 2015 version of Wetland Mitigation and Monitoring Guidelines and the three demonstration sites are using them in their vernal pool mitigation monitoring projects.