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Methods Assessment and Improvement of Infiltration Analyses to Support Estimates of Recharge and Initial Abstraction

PI: Dr. Michael Young, Division of Hydrologic Sciences, Desert Research Institute, 755 E. Flamingo Road, Las Vegas, NV 89119 USA

Co-PI: Dr. Steve Mizell, Division of Hydrologic Sciences, Desert Research Institute, 755 E. Flamingo Road, Las Vegas, NV 89119 USA

COE Collaborator: Brian Skahill, USACE ERDC, Vicksburg, MS; Steven Grant, USACE ERDC, Hanover, NH

Problem Statement

Infiltration characteristics of different ground surfaces (turf, natural desert) in the Las Vegas Valley can greatly influence the amount of precipitation that recharges deep soil or which becomes surface runoff. The overall goal of this research is to improve predictions of runoff levels by incorporating better estimates of soil infiltration in precipitation-runoff models. This subtask will build on the geomorphic work conducted in subtask 21.2, in which soil surfaces of different ages and distinguishing characteristics are identified. This task seeks to improve the methods by which infiltration is estimated in Las Vegas Valley through the use of field measurements taken at locations with distinctly different surface morphologic features. Hydraulic properties of these soil surfaces will be obtained using the tension infiltrometer, and physical properties will be obtained through material sampling and laboratory analysis of texture or other distinguishing characteristics. The field hydraulic property data will be correlated to surface texture and geomorphic features using covariance and regression analyses. Concurrently, it is foreseen that USACE collaborators will assist in the implementation of the findings into one or more simulation codes currently in use by the Corp of Engineers, so that the new methodologies can available for use by local stakeholders as soon as feasible. The relationships would then be upscaled to a level of greatest benefit to local stakeholders. Implementation into simulation codes is foreseen to occur in Year 2.

Objectives

1. To characterize hydraulic properties for surface materials that exist in distinct land-use classes and geomorphic surfaces.
2. To use results from subtask 21.2 and correlate hydraulic properties to surface materials.
3. To improve in the methodologies of upscaling the results to the watershed scale.
4. To collaborate with USACE scientists/engineers so that the relationships are implemented into simulation codes used by USACE.

Methods

1. Obtain detailed land use classes for the lower LV valley and soil surface maps obtained under subtask 21.2 for the upper valley.
2. Identify measurement locations for major land use classes in the lower valley, and collaborate with Adams/Bullard (subtask 21.2) regarding locations in upper valley, chosen according to geomorphic surface characteristics.
3. Collect data on the hydraulic characteristics of land surface materials for each land surface class, including collection of materials for laboratory analysis of texture, measurement of in-situ hydraulic conductivity with tension infiltrometers. Tests will be conducted at the same location as the rainfall simulator tests conducted under subtask 21.2.
4. Evaluate the correlation between hydraulic properties and surface features through the use of statistical analyses.
5. Using a GIS platform and the results from subtask 21.2, apply the range of hydraulic properties measured in the field to each surface and soil class.
6. Work with USACE collaborators to ensure that the approaches outlined above provide an improved dataset – including the effects of temperature on infiltration – which can be implemented into simulation/engineering design codes that are used by USACE.

Data Needs (italicized text indicates data collected in this subtask)

1. Land-use classes in DEM/GIS format for the urbanized portions of the LV Valley.
2. Geomorphic maps (DEM/GIS) delineating surfaces of different ages or other distinguishing characteristics.
3. Locations chosen in 21.2 for rainfall simulation tests.
4. Feedback from USACE collaborators regarding the form and format of data needed for simulation codes.
5. Hydraulic properties (Ksat, pore size parameters) of soil surfaces .
6. Textural analyses of soil surface material .

Deliverables

1. Actual field data on hydraulic properties for different soil classes in the Las Vegas Valley (which can be used almost immediately by the SNWA and CCRFCD).
2. DEM/GIS maps with estimates of hydraulic properties, and hence surface runoff and infiltration potentials.
3. Established framework for more extensive characterization of soil surfaces during Year 2.