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Water-Balance/Darcian Recharge model for deep water-table


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Created: Jun 03, 2020 at 10:42 p.m.
Last updated: Jun 05, 2020 at 9:51 p.m.
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Abstract

Analytical solutions for Darcy’s flux and volumetric moisture content were derived defining recharge for a phreatic aquifer with a deep water table. A lumped parameter conceptualization was used, extending through the deep vadose zone from effective infiltration at the bottom of the root zone to recharge at the water table. A physics-based approach combining Darcy’s law and a dynamic water balance was applied, giving a model based on commonly measured hydraulic properties of the vadose zone. The analytical solution for flux was based on linearization of the one-dimensional differential equation for vertical Darcian flow in the vadose zone using the Kirchhoff potential and the Gardner exponential model for hydraulic conductivity. The analytical solution for the average volumetric moisture content was based on the Gardner-Kozeny exponential model for the soil moisture characteristic curve. A linear ordinary differential equation was obtained by assuming the Gardner and Gardner-Kozeny pore-size distribution parameters are equal, and superposition was used to apply the model for any number of successive infiltration events. Application of the water-balance/Darcian recharge model was demonstrated at a field site in central Florida, USA. The simulated recharge flux compared well with recharge estimated by independent analysis of water-table fluctuations, and calibration was achieved using measured vadose zone properties and adjusting only saturated hydraulic conductivity. We propose that the analytical lumped-parameter model provides a simple physics-based method to estimate the flux recharging a phreatic aquifer with a relatively thick vadose zone, and present a simple spreadsheet-based implementation of the water-balance/Darcian model.

Manuscript currently in review: Abrokwah, K.O., and A.M. O'Reilly, IN REVIEW. A simple water-balance/Darcian recharge model for a vadose zone with a deep water table: Groundwater (submitted 6/2020)

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Resource Level Coverage

Spatial

Coordinate System/Geographic Projection:
WGS 84 EPSG:4326
Coordinate Units:
Decimal degrees
Longitude
-81.6342°
Latitude
28.4836°

Temporal

Start Date:
End Date:

Content

README.txt

The Excel Workbook "Water-Balance--Darcian-Recharge_model_v0.2.xlsx" contains the Water-Balance/Darcian Recharge model documented in and available at		
		
Abrokwah, K.O., and A.M. O'Reilly, IN REVIEW. A simple water-balance/Darcian recharge model for a vadose zone with a deep water table: Groundwater (submitted 6/2020)		
		
Hydroshare:  O'Reilly, A.M., and K.O. Abrokwah (2020). Water-Balance/Darcian Recharge model for deep water-table, HydroShare, http://www.hydroshare.org/resource/44272847af55482fa9ffd79024d6b952		
		
Version history		
#	Date		Remarks
0.1	3-Jun-2020	Initial internal Beta version  (active links to data from Sumner (1996) at field site in Orange County, Florida)
0.2	5-Jun-2020	Beta version, use spreadsheet equations in the Groundwater paper
0.3	5-Jun-2020	Initial public Beta version release of model (user must enter data: Effective infiltration,  ? (if available), Measured recharge (if available))

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The Excel Workbook "Water-Balance--Darcian-Recharge_data.xlsx" contains the field data used for Water-Balance/Darcian Recharge model documented in and available at	
	
Abrokwah, K.O., and A.M. O'Reilly, IN REVIEW. A simple water-balance/Darcian recharge model for a vadose zone with a deep water table: Groundwater (submitted 6/2020)	
	
Hydroshare:  O'Reilly, A.M., and K.O. Abrokwah (2020). Water-Balance/Darcian Recharge model for deep water-table, HydroShare, http://www.hydroshare.org/resource/44272847af55482fa9ffd79024d6b952
	
Worksheet	Contents
Meas_Rech_EI	measured values for precipitation, actual ET, groundwater level; computed values of effective infiltration and groundwater recharge
Meas_theta	measured values for volumetric moisture content at an east (E) location and west (W) location; computed value for wieghted average below 0.3 m depth
SMCC		laboratory measured pressure - volumetric moisture content

Further details regarding the field site and measured data are provided by Sumner (1996) and OReilly (2004)

OReilly, A.M. 2004. A Method for Simulating Transient Ground-Water Recharge in Deep Water-Table Settings in Central Florida by Using a Simple Water-Balance/Transfer-Function Model. USGS Scientific Investigations Report 2004-5195, 49 p.

Sumner, D.M. 1996. Evapotranspiration from successional vegetation in a deforested area of the Lake Wales Ridge, Florida. USGS Water-Resources Investigations Report 96-4244, 37 p.

Resource Specific

Software
Programming Language Microsoft Excel (R)
Operating System Microsoft Windows (R)
Release Date 06/04/2020
Version 0.3 beta

How to Cite

O'Reilly, A. M., K. O. Abrokwah (2020). Water-Balance/Darcian Recharge model for deep water-table, HydroShare, http://www.hydroshare.org/resource/44272847af55482fa9ffd79024d6b952

This resource is shared under the Creative Commons Attribution CC BY.

 http://creativecommons.org/licenses/by/4.0/
CC-BY

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