Replenish (Volumetric Water Benefit Accounting) calculators for estimating water volume and quality changes from land management interventions, check dams, recharge wells, ditch water level raising, roof rainwater harvesting, invasive aquatic plant clearance and wastewater treatment systems — plus an indicator-based assessment tool for sustainable water management in catchments and aquifers
This is a personal repository of screening tools for water stewardship. I built them to work through methods I encountered in practice — to understand what each one assumes, where it breaks down, and how sensitive its answer is to parameters that are rarely measured. They are shared in case they are useful to others working on the same problems. Anyone is free to use them.
The tools fall into two groups that answer different questions. The replenish calculators estimate the volumetric water benefit of a specific intervention: additional infiltration or aquifer recharge, reduced runoff, increased groundwater storage, a withdrawal avoided by harvesting rainwater, a change in evaporative loss following invasive plant clearance, or an effective volume treated. The SWM assessment tool asks a separate question — whether water is managed sustainably in the catchment or aquifer where those interventions sit. A well-evidenced replenish volume in a basin with no functioning allocation or compliance regime is a weaker claim than the volume alone suggests, which is why the two sit alongside each other.
All are screening-level: daily, monthly or steady-state models, and structured expert judgement in the case of the indicator assessment. They are intended to test whether an intervention or a catchment is worth closer attention, and to show which parameters govern the answer — not to replace calibrated or numerical modelling for design, permitting or assured reporting.
Several of the tools will return a result of zero, or of the opposite sign to the one expected, when the inputs imply it. That is deliberate. An intervention that spills most of what it captures, or that replaces one evaporating surface with a wetter one, has no volumetric benefit to claim, and a calculator that cannot say so is not much use.
Evaluate the runoff reduction due to land use and land cover changes using the NRCS Curve Number method.
This calculator uses the Natural Resources Conservation Service (NRCS) Curve Number method to estimate runoff generation before and after land management changes. By comparing pre-project and post-project scenarios, it quantifies the reduction in runoff (which becomes additional infiltration).
Best for:
Calculate the additional annual infiltration from check dams using detailed water balance and Green-Ampt infiltration modelling.
This calculator simulates the daily water balance of a check dam, accounting for inflow from catchment runoff, evaporation from the water surface, and infiltration through the dam bed using the Green-Ampt equation. It tracks storage volume, spillage, and cumulative infiltration over time.
Key processes modelled:
Estimate the additional groundwater stored between drainage ditches when ditch water levels are raised, with the water table capped at ground level.
This calculator computes steady-state water-table profiles between two parallel ditches (Dupuit–Forchheimer solution with uniform recharge, after Bear) for baseline and raised ditch levels, and integrates the difference to give the one-off increase in drainable groundwater storage over the channel length. Where the water table reaches ground level, a seepage zone forms and rejected recharge is reported as an annual surface runoff flux.
Key processes modelled:
Best for:
Estimate managed aquifer recharge from a recharge well or dry well, routing captured runoff through daily well acceptance capacity and reporting net replenish under VWBA 2.0.
This calculator generates daily catchment runoff using the SWAT variable-retention Curve Number method, then routes the captured fraction through the daily acceptance capacity of the well. Wells screened below the water table use a Dupuit–Thiem radial-flow capacity that can be coupled to the modelled mound, so acceptance declines as the permitted head rise is consumed. Dry wells above the water table use a design infiltration rate applied to the wetted sidewall and base. Accepted water is converted to recharge through a transmission factor, lagged through the vadose zone, and netted against a without-project counterfactual.
Key processes modelled:
Best for:
Features:
Estimate the volume of water supplied from roof rainwater harvesting using a daily tank water balance, for a single installation or a portfolio of buildings uploaded as a CSV schedule.
Daily rainfall over the roof plan area is converted to tank inflow through an initial abstraction and an adjustable collection efficiency, then routed through tank storage against a demand that can be limited to operating days and open months. Yield, overflow, unmet demand and tank losses are tracked daily under either the yield-after-spillage or yield-before-spillage operating rule, and the balance is reconciled and reported. The replenish estimate is the volume actually drawn from the tank, netted against a displacement fraction.
Key processes modelled:
Best for:
Features:
Estimate the change in evaporative loss from clearing invasive aquatic vegetation, using measured macrophyte evapotranspiration ratios, a regional evaporation profile and an explicit regrowth trajectory.
Clearance does not remove a water demand; it replaces one evaporating surface with another. The benefit is the difference between the evapotranspiration of the invaded stand and the evaporation of whatever replaces it, and it can be of either sign. The calculator applies a species ET ratio referenced to open-water evaporation, adjusts it for the advective inflation that affects tank and lysimeter measurements, and tracks logistic regrowth between follow-up operations over a monthly accounting horizon.
Key processes modelled:
Best for:
Features:
Calculate volumetric water benefits from wastewater treatment projects using the VWBA 2.0 methodology for water quality improvements.
This calculator quantifies the effective volume of water improved through treatment by analyzing water quality improvements across multiple parameters. It calculates a quality factor based on how much each parameter (BOD, COD, TSS, nutrients, DO, etc.) improves toward meeting environmental standards.
Best for:
Features:
A structured, indicator-based assessment of how sustainably water resources are managed in a catchment or aquifer. Unlike the replenish calculators above, which quantify volumetric benefits of individual interventions, this tool evaluates the governance, management and outcomes context in which those interventions sit.
You score a set of indicators for surface water (environmental flows) and groundwater (aquifers), grouped under three pillars: legislative and institutional support; planning, management and implementation; and monitoring, compliance and outcomes. Scores roll up into a percentage-based sustainability classification for each component, from “not meeting targets” to “meeting standards”, alongside a diagnostic view of enabling conditions.
Key features:
Best for:
For Curve Number and Check Dam Calculators: Upload climate data in CSV format with daily precipitation and potential evapotranspiration (PET) records for your project location. Results include annual average recharge estimates, detailed daily outputs, and visualizations of temporal dynamics.
For Volume Treated Calculator: Upload water quality data in CSV format or manually select parameters to evaluate. Enter inlet and outlet concentrations for parameters like BOD, COD, TSS, nutrients, and dissolved oxygen. The calculator quantifies volumetric water benefits based on water quality improvements toward environmental standards using VWBA 2.0 methodology.
For the Recharge Well Calculator: Upload daily precipitation and PET data in the same CSV format used by the Curve Number and Check Dam calculators, then describe the contributing catchment, the well geometry and its position relative to the water table. Results include annual net replenish, a closed daily water balance, water-table and well-level charts with rainfall overlaid, and an infiltration-rate sensitivity sweep showing whether the estimate is limited by well capacity, routing storage or runoff supply.
For the Roof Rainwater Harvesting Calculator: Upload daily rainfall as Date and Rainfall (mm); several gauges can be supplied as additional columns in the same file. Describe one installation directly, or upload a CSV schedule of many buildings with their roof areas, tank sizes, demands and operating calendars. Results include annual tank yield and net replenish, a closed daily water balance, storage and monthly balance charts, and a capacity sweep identifying whether demand, runoff supply or storage is the binding constraint.
For the Aquatic Invasive Plant Clearance Calculator: No daily data upload is required — enter the cleared area and mat cover, select the species, and supply a monthly open-water evaporation profile either from the built-in generator, from reference ET with an open-water coefficient, or as a twelve-row CSV. Set the regrowth and follow-up regime, which usually matters more than the ET ratio. Results include monthly and annualised net benefit, the break-even ET ratio, and a sensitivity sweep across the published range for the selected species.
For the Ditch Level Raising Calculator: No data upload is required — enter the strip geometry, aquifer parameters (hydraulic conductivity, specific yield, recharge) and baseline and raised ditch water levels directly. Results include the additional groundwater volume stored, water-table profiles, seepage zone extent, rejected recharge, and a downloadable CSV of the computed profiles.
Each tool guides you through the data and parameter input needed to generate comprehensive reports of your water stewardship benefits.