Low Flows 2000 Enterprise software

Low Flows 2000 is a geographically orientated hydrological software package for estimating flow statistics in rivers where flow measurements are not available. The system deploys regional hydrological models originally developed by the Centre for Ecology and Hydrology for predicting natural river flows coupled with deterministic procedures for incorporating the impacts of water use into the estimation process. Low Flows 2000 and the underpinning science has been extensively published within the scientific literature.

The software enables a user to select a point on a digital river network (rivers mapped at a 1:50,000 scale) and automatically define the catchment above that point using a digital terrain model (incorporated in the software) or a 'nearest neighbour' approach (defining catchment membership of grid cells by proximity to river reaches). Contextual information, such as map backdrops, can be browsed into graphical user interface for contextual purposes as either image files or ESRI ShapeFiles.

Low Flows 2000 user interface showing catchment definition

The Natural Low Flow Estimation option uses the defined catchment boundary to automatically derive relevant catchment characteristics from internally-held spatial data sets. The CEH Wallingford hydrological models are then applied to estimate the following natural flow statistics for that catchment.

• Mean annual flow
• Mean monthly flows
• Annual flow duration statistics
• Monthly flow duration statistics
• User-defined seasonal flow duration statistics
• Base flow index (BFI)

The Influenced Low Flow Estimation option uses the catchment boundary to identify all influencing 'features' (abstractions, discharges and impounding reservoirs) affecting the natural flow regime. These are summed to produce a 'net influence profile' representing the average monthly impacts of water use within the catchment. A set of 'influenced' flow statistics are then derived by incorporation of the net influence profile with the natural flow statistics, derived as previously described. These influenced flow statistics represent the flows that would be observed in the river given the natural hydrological conditions and the impacts of water use within the catchment.

The software also enables spot measurements of river flows to be compared to the predicted flows for evaluation purposes.

Estimated natural and artificially influenced flow duration curves

The software can also be used as a scenario tool to simulate the impacts of including new water use features, such as the impact of diverting water, abstracting water, discharging water and installing impoundments/reservoirs. Additionally, sensitivity-type analysis can be performed by modelling the impact of global changes to water use.

Scenario modelling within Low Flows 2000

Other hydrologic functionality included in Low Flows 2000 includes the automatic generation of Residual Flow Diagrams showing the natural and influenced flow components along a river stretch. These are derived by progressive influenced flow estimation at river confluences along the User-defined stretch. The results are presented as longitudinal profiles of river flow, river network overlays), tabulated statistics on a stretch basis and ShapeFile format with summary statistics.

Residual Flow Diagram – Longitudinal section

Residual Flow Diagram – River network overlay