RIPGIS-NET: a GIS tool for riparian groundwater evapotranspiration in MODFLOW

RIPGIS-NET, an Environmental System Research Institute (ESRI's) ArcGIS 9.2/9.3 custom application, was developed to derive parameters and visualize results of spatially explicit riparian groundwater evapotranspiration (ETg), evapotranspiration from saturated zone, in groundwater flow models for ecohydrology, riparian ecosystem management, and stream restoration. Specifically RIPGIS-NET works with riparian evapotranspiration (RIP-ET), a modeling package that works with the MODFLOW groundwater flow model. RIP-ET improves ETg simulations by using a set of eco-physiologically based ETg curves for plant functional subgroups (PFSGs), and separates ground evaporation and plant transpiration processes from the water table. The RIPGIS-NET program was developed in Visual Basic 2005, .NET framework 2.0, and runs in ArcMap 9.2 and 9.3 applications. RIPGIS-NET, a pre- and post-processor for RIP-ET, incorporates spatial variability of riparian vegetation and land surface elevation into ETg estimation in MODFLOW groundwater models. RIPGIS-NET derives RIP-ET input parameters including PFSG evapotranspiration curve parameters, fractional coverage areas of each PFSG in a MODFLOW cell, and average surface elevation per riparian vegetation polygon using a digital elevation model. RIPGIS-NET also provides visualization tools for modelers to create head maps, depth to water table (DTWT) maps, and plot DTWT for a PFSG in a polygon in the Geographic Information System based on MODFLOW simulation results.     

Impact of land-surface elevation and riparian evapotranspiration seasonality on groundwater budget in MODFLOW models

Riparian groundwater evapotranspiration (ETg) constitutes a major component of the water balance especially in many arid and semi-arid environments. Although spatial and temporal variability of riparian ETg are controlled by climate, vegetation and subsurface characteristics, depth to water table (DTWT) is often considered the major controlling factor. Relationships between ETg rates and DTWT, referred to as ETg curves, are implemented in MODFLOW ETg packages (EVT, ETS1 and RIP-ET) with different functional forms. Here, the sensitivity of the groundwater budget in MODFLOW groundwater models to ETg parameters (including ETg curves, land-surface elevation and ETg seasonality) are investigated. A MODFLOW model of the hypothetical Dry Alkaline Valley in the Southwestern USA is used to show how spatial representation of riparian vegetation and digital elevation model (DEM) processing methods impact the water budget when RIPGIS-NET (a GIS-based ETg program) is used with MODFLOW’s RIP-ET package, and results are compared with the EVT and ETS1 packages. Results show considerable impact on ETg and other groundwater budget components caused by spatial representation of riparian vegetation, vegetation type, fractional coverage areas and land-surface elevation. RIPGIS-NET enhances ETg estimation in MODFLOW by incorporating vegetation and land-surface parameters, providing a tool for ecohydrology studies, riparian ecosystem management and stream restoration.     

A correction model for conditional bias in selective mining operations

A nonlinear correction functionK(Z*) is proposed to transform any initial linear grade estimatorZ* into a conditional unbiased estimatorZ**=K(Z*) with reduced conditional estimation variance. Such a corrected estimator allows more accurate prediction of ore reserves at any level of selection performed during the mine lifetime. The correction is based upon an analytical or isofactorial representation of a bivariate distribution model of true gradeZ and its estimatorZ*. This correction model allows derivation of conditional estimation variances for both estimatorsZ* andZ** and provides a solution to the problem of change of support. A case study is presented and performance of the proposed correction model is evaluated in terms of actual conditional bias and mean squared errors. Results obtained stress the practical importance of the correction model in selective mining operations.