Storativity Calculator
Calculate Storativity (S)
Select aquifer type and enter the required parameters.
About the Storativity Calculator
The Storativity Calculator is a free online tool designed to help hydrogeologists, engineers, students, and water resource professionals accurately compute storativity (also known as storage coefficient) based on established scientific principles in groundwater hydrology. Storativity is a fundamental parameter that quantifies how much water an aquifer releases or stores in response to changes in hydraulic head.
This Storativity Calculator strictly adheres to peer-reviewed formulas from classic hydrogeology texts such as Freeze and Cherry (1979) "Groundwater" and other authoritative sources. It distinguishes between confined and unconfined aquifers to ensure precise, reliable results.
What is Storativity?
Storativity (S), or storage coefficient, is defined as the volume of water that an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in hydraulic head perpendicular to that surface. It is a dimensionless quantity.
- In confined aquifers: S = Ss × b, where Ss is specific storage and b is aquifer thickness. Values are typically small (10⁻⁵ to 10⁻³), as water is released primarily through compression of the aquifer matrix and expansion of water.
- In unconfined aquifers: S ≈ Sy + (Ss × b), where Sy (specific yield) dominates, reflecting gravity drainage. Sy ranges from 0.01 to 0.35, making S much larger (0.05–0.3).
Importance of Storativity in Hydrogeology
Storativity is crucial for understanding aquifer behavior under pumping or recharge stress. It directly influences drawdown predictions in models like the Theis equation and affects groundwater resource management. Accurate storativity values help prevent overexploitation, predict land subsidence in confined systems, and optimize well design.
In confined aquifers, low storativity means significant head changes over large areas for relatively small water volumes extracted. In unconfined aquifers, higher storativity from specific yield allows more water release with less head decline.
User Guidelines
To use this Storativity Calculator:
- Select the aquifer type (confined or unconfined).
- Enter values in consistent units (e.g., meters for thickness and 1/m for Ss).
- For unconfined aquifers, specific yield (Sy) is the primary contributor—Ss × b is often negligible but included for completeness.
- Click "Calculate" for instant results.
Typical ranges: Ss = 10⁻⁷ to 10⁻⁴ m⁻¹; Sy = 0.1–0.3 for sands; b varies by site.
When and Why You Should Use This Tool
Use the Storativity Calculator during aquifer testing analysis, groundwater modeling (e.g., MODFLOW), environmental impact assessments, or water supply planning. It is essential when interpreting pumping test data, estimating sustainable yield, or evaluating aquifer storage for managed recharge projects.
In regions facing water scarcity, accurate storativity helps quantify available groundwater storage and predict responses to climate change or increased demand.
Purpose of the Storativity Calculator
The primary purpose is to provide a simple, accurate, and accessible tool for computing storativity based on authentic hydrogeologic principles. It promotes education and professional practice by making complex calculations instant and error-free.
Detailed Explanation of Formulas
The formulas used are derived from the definition of storage properties:
Specific storage (Ss) = ρg (α + nβ), where ρ is water density, g is gravity, α is aquifer compressibility, n is porosity, and β is water compressibility (from Jacob, 1940; verified in numerous studies).
However, this calculator uses direct inputs for practical application, as Ss is often measured or estimated from field tests.
For confined aquifers: S = Ss × b (dimensionless).
For unconfined: S = Sy + Ss × b (Sy dominates; Ss term from elastic storage).
Applications in Groundwater Management
Storativity is used in transient flow equations to model cone of depression propagation. Low S in confined aquifers leads to rapid drawdown spread, risking regional depletion. High S in unconfined aquifers supports higher yields but increases vulnerability to contamination.
Case studies, such as the Ogallala Aquifer (unconfined, high Sy) versus artesian aquifers in Florida (low S), highlight its role in sustainability.
Limitations and Considerations
This tool assumes homogeneous, isotropic conditions. Real aquifers may exhibit heterogeneity, anisotropy, or partial penetration effects. For advanced cases, consult full pumping test analysis software.
Storativity values should ideally come from site-specific aquifer tests for highest accuracy.
References and Further Reading
Learn more about storativity on the Storativity Calculator Wikipedia page (note: links to specific storage, closely related).
Key references: Freeze, R.A. and Cherry, J.A. (1979). Groundwater; Theis (1935); Jacob (1940).
This tool is provided by Agri Care Hub, your resource for agricultural and water management tools.
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