HARE Irrigation Project
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SWAT Results

Two continuous SWAT simulations have now been completed for the approximately 161.95 km² Hare River watershed. The model represents 17 hydrologically connected subbasins and uses daily meteorological forcing for the period 2020–2025.

The present results provide an initial continuous assessment of watershed runoff, evapotranspiration, subsurface flow, groundwater contribution, daily Hare River discharge, upland erosion and sediment routing.

The two simulations produced similar overall water-balance and sediment behaviour, providing a useful preliminary stability check on the current model configuration.

Calibration status: the present results are from a successfully functioning but not yet formally calibrated SWAT model. Formal streamflow calibration requires observed discharge covering the same period as the meteorological forcing.
Current result summary

Key SWAT Findings

Watershed

161.95 km²

Continuous watershed model represented by 17 subbasins.

Largest Daily Flow

211.6 m³/s

Largest outlet daily flow identified in Simulation 1, occurring on 15 April 2024.

Average Sediment Yield

58.4 Mg/ha

Average upland sediment yield from Simulation 2.

Channel Deposition

96.23%

Strong depositional behaviour identified by the SWAT sediment diagnostics.

Surface Runoff

267.63 mm

Basin-average surface runoff from Simulation 2.

Groundwater Return Flow

182.06 mm

Simulated groundwater contribution to streamflow in Simulation 2.

Simulation configuration

Continuous SWAT Simulation

Setting Current SWAT Configuration
Watershed area 161.95 km²
Subbasins 17
Climate period 1 January 2020 – 31 December 2025
Warm-up period 2020
Primary interpretation period 2021–2025
Output time step Daily
Precipitation method Daily NASA POWER climate forcing
Weather source NASA POWER, 16 spatial grid points
Simulation 1 Initial continuous baseline simulation
Simulation 2 Hare-specific weather-generator assignment
Model stability

Simulation 1 and Simulation 2 Water Balance

The second simulation produced a water balance very similar to the first run. This indicates that the principal watershed response was not substantially changed by the Hare-specific weather-generator assignment.

Water-Balance Component Simulation 1 Simulation 2 Change
Precipitation 1665.50 mm 1665.50 mm 0.00 mm
Potential evapotranspiration 1570.70 mm 1570.70 mm 0.00 mm
Actual evapotranspiration 955.50 mm 928.90 mm −26.60 mm
Surface runoff 262.27 mm 267.63 mm +5.36 mm
Lateral flow 247.20 mm 250.62 mm +3.42 mm
Percolation 209.48 mm 224.09 mm +14.61 mm
Groundwater return flow 168.60 mm 182.06 mm +13.46 mm
Deep recharge 10.47 mm 11.20 mm +0.73 mm
Average Curve Number 77.62 77.62 No change
Average upland sediment yield 59.15 Mg/ha 58.40 Mg/ha −0.75 Mg/ha
Result: the similarity of the two simulations provides a useful preliminary stability check. Simulation 2 is therefore retained as the present reference configuration while detailed output interpretation continues.
Basin response

Simulation 2 Hydrological Ratios

Streamflow / Rainfall

0.42

Approximately 42% of precipitation contributes to simulated water yield.

ET / Rainfall

0.56

Approximately 56% of precipitation is represented as actual evapotranspiration.

Baseflow / Total Flow

0.62

Groundwater and subsurface processes form an important part of the simulated streamflow.

Surface / Total Flow

0.38

Surface runoff represents approximately 38% of simulated flow.

Percolation / Rainfall

0.13

Approximately 13% of precipitation percolates beyond the soil profile in the simulation.

Deep Recharge / Rainfall

0.01

Only a small portion of precipitation reaches the deep aquifer.

Visual result summary

Simulation 2 Hydrology Infographic

The infographic below summarizes the principal hydrological results reported by the SWAT Error Checker for Simulation 2, including precipitation, evapotranspiration, surface runoff, lateral flow, percolation, groundwater return flow and the principal water-balance ratios.

Hare River SWAT Simulation 2 hydrology summary showing precipitation, potential and actual evapotranspiration, surface runoff, lateral flow, percolation, groundwater return flow, recharge and water-balance ratios.
Hare River SWAT Hydrology Summary — Simulation 2. The figure presents the main basin-scale hydrological indicators from the successful second continuous SWAT run. Values shown are model outputs and remain subject to formal calibration against same-period observed flow.
Seasonal behaviour

Monthly Basin Response — Simulation 2

The monthly SWAT results show strong seasonal variation in rainfall, surface runoff, subsurface flow, water yield, evapotranspiration and sediment production.

Month Rainfall
(mm)		 Surface Runoff
(mm)		 Lateral Flow
(mm)		 Water Yield
(mm)		 Actual ET
(mm)		 Sediment Yield
January 44.10 15.81 5.35 33.72 39.20 1.07
February 40.43 2.70 3.18 10.13 43.98 1.56
March 152.88 28.18 16.82 46.60 107.67 8.20
April 332.13 76.62 50.13 131.68 120.38 14.67
May 218.20 32.16 39.87 92.20 113.89 7.39
June 106.50 4.83 12.54 38.88 94.41 1.03
July 117.42 5.48 15.10 35.08 75.85 1.16
August 119.09 10.44 20.10 44.09 66.62 3.11
September 126.06 7.47 18.42 40.59 68.97 2.00
October 221.84 36.59 43.12 103.29 83.48 8.22
November 152.40 46.79 23.48 105.20 66.64 9.86
December 34.20 0.54 2.50 30.08 47.43 0.13

April is the dominant month in the present simulation, with approximately 332.13 mm of rainfall, 76.62 mm of surface runoff and 131.68 mm of water yield.

A second period of strong hydrological response occurs during October and November.

Hare River outlet

Reach 17 Daily Streamflow

Reach 17 represents the downstream outlet of the current SWAT watershed and has a contributing area of approximately 161.9 km², corresponding closely to the Hare Weir catchment.

The annual maximum daily outlet flows identified from the first continuous SWAT simulation are:

Year Date Maximum Daily Flow Interpretation
2021 1 January 2021 113.2 m³/s Influenced by the large rainfall event at the end of the 2020 warm-up period.
2022 16 April 2022 78.75 m³/s Annual maximum daily flow.
2023 17 November 2023 64.18 m³/s Annual maximum daily flow.
2024 15 April 2024 211.6 m³/s Largest daily discharge in the current simulation.
2025 10 March 2025 70.28 m³/s Annual maximum daily flow.
Time-scale distinction: these values are SWAT daily simulated flows. They are not directly equivalent to an instantaneous or short-duration design-flood peak.
Complementary models

SWAT and HEC-HMS Results

The HARE reassessment uses SWAT and HEC-HMS for complementary purposes rather than treating them as identical hydrological models.

Model Key Result Meaning
HEC-HMS 50-year event peak: 114.4 m³/s Event-based design-flood hydrograph at the Hare Weir.
SWAT Maximum current simulated daily flow: 211.6 m³/s Continuous daily watershed response during the 2020–2025 simulation period.

The numerical values should not be interpreted as directly comparable peak statistics. HEC-HMS resolves an event hydrograph at a much shorter computational interval, while the current SWAT output represents daily average simulated discharge.

Sediment assessment

Upland Erosion and Channel Deposition

Sediment behaviour has emerged as one of the most important findings from the first Hare SWAT simulations.

Average Upland Yield

58.4 Mg/ha

Simulation 2 basin-average upland sediment yield.

Maximum HRU Yield

2,538.1 Mg/ha

Maximum simulated upland sediment yield identified by the SWAT Error Checker.

Channel Deposition

96.23%

Error Checker indication of very strong sediment deposition within the simulated stream system.

1 Mg = 1 metric tonne = 1,000 kg

The simulated in-stream sediment change in Simulation 2 was approximately −56.2 Mg/ha. The negative value indicates that the model is representing substantial net sediment deposition within the channel system rather than simple downstream transport of all eroded material.

Interpretation: the sediment outputs are not yet calibrated against measured sediment concentrations or sediment-discharge observations. They should therefore be interpreted as modelled erosion and deposition indicators rather than precise measured sediment loads.
Visual sediment summary

Simulation 2 Sediment Infographic

The sediment infographic summarizes the principal SWAT Error Checker outputs from Simulation 2 and shows how upland erosion, runoff, channel transport and deposition are interpreted within the Hare watershed.

Hare River SWAT Simulation 2 sediment summary showing average and maximum upland sediment yield, surface runoff, in-stream sediment change, erosion hotspot and sediment-management implications.
Hare River SWAT Sediment Summary — Simulation 2. The figure highlights the basin-average sediment yield, the localized maximum erosion hotspot and the negative in-stream sediment change. These results are interpreted as modelled indicators and are not yet calibrated sediment-load measurements.
Spatial erosion response

Land-Use Contribution to Sediment Yield

The SWAT land-use summary shows that erosion is not distributed uniformly across the watershed.

SWAT Land Use Approx. Area Curve Number Surface Runoff Sediment Yield
AGRL
Agricultural land 		42.37 km² 83.00 381.43 mm 165.47 Mg/ha
BARR
Bare ground 		0.58 km² 91.00 663.81 mm 1,549.33 Mg/ha
FRST
Forest 		55.76 km² 73.00 166.62 mm 0.77 Mg/ha
RNGB
Range brush 		18.97 km² 74.00 171.92 mm 21.96 Mg/ha
RNGE
Range grasses 		33.56 km² 79.00 265.62 mm 31.91 Mg/ha

The most striking result is the BARR bare-ground class. It occupies only approximately 0.58 km², but the model assigns it a very high runoff response and localized sediment yield.

Important: the value of 1,549.33 Mg/ha is not the average erosion rate for the entire watershed and should not be interpreted as the amount of sediment arriving at the Hare intake. It represents a localized modelled response associated with the bare-ground land-use class.
Erosion hotspot

Highest Simulated Sediment-Yield HRU

HRU

160

Highest simulated upland sediment-yield HRU identified in the present analysis.

Subbasin

6

The erosion hotspot is located within SWAT Subbasin 6.

Land Use

BARR

Bare or exposed ground forms the dominant modelled erosion condition.

This result provides a clear target for future spatial review. HRU 160 can be compared with satellite imagery, slope, land-cover condition and field observations to determine whether the simulated erosion hotspot corresponds to a physically disturbed or exposed area.

Model and field evidence

Field Evidence of Sedimentation at the Hare Weir

The SWAT sediment results can now be considered together with current field photographs and video of the existing Hare diversion structure.

Hare diversion weir sedimentation infographic showing substantial upstream and downstream sediment deposition and the remaining active flow channel.

Present Sedimentation Condition at the Hare Diversion Weir. Field observations show substantial sediment accumulation both upstream and downstream of the structure. Deposited gravel, sand and finer material occupy a large part of the river section, while the present active flow is confined to a much narrower channel.

The photographs do not provide a direct measurement of sediment depth, deposited volume or annual sediment load. Nevertheless, they provide independent physical evidence that sediment transport and deposition are important processes at the diversion site.

Combined interpretation: SWAT predicts substantial upland erosion and strong in-stream deposition, while current field observations independently show major sediment accumulation at the Hare diversion structure. The two lines of evidence are physically consistent.
Engineering significance

Implications for the Hare Diversion Headworks

The combined watershed modelling and field evidence indicates that sediment management should be treated as a principal design issue in any reassessment or rehabilitation of the Hare diversion headworks.

The reconstructed design should therefore examine the adequacy and arrangement of sediment-control measures including:

  • under-sluices or scour sluices near the diversion weir;
  • sediment flushing routes;
  • sediment exclusion at the canal intake;
  • intake alignment relative to sediment-carrying river flow;
  • possible desilting or settling facilities;
  • sediment ejectors where appropriate; and
  • operational flushing during high-flow conditions.

Final hydraulic sizing of these measures will require additional information including sediment grain-size distribution, sediment concentration, intake geometry, design canal discharge, river-water levels and available flushing discharge.

SWAT diagnostics

Error Checker and Model Diagnostics

The SWAT Error Checker provides useful screening indicators for model interpretation. These warnings do not by themselves demonstrate that a parameter value is incorrect.

Diagnostic Current Result Interpretation
Lateral flow 250.62 mm Error Checker notes relatively strong lateral-flow contribution.
Groundwater return flow 182.06 mm Lower than lateral flow; flagged for future calibration review.
Water yield Screening warning The model may be producing relatively high water yield.
Channel sediment deposition 96.23% Very strong modelled depositional behaviour; important for sediment assessment.
Bare-ground erosion Very high BARR class identified as a major localized erosion hotspot.
Calibration principle: Error Checker warnings are used to identify parameters and processes requiring review. They are not sufficient justification for arbitrary parameter adjustment.
Interpretation limits

Calibration Status of the Results

The present SWAT results describe the behaviour of the current model configuration. They are not yet formal calibration results.

The current meteorological forcing covers 2020–2025, whereas the historical Hare River discharge observations recovered from the original project study cover 1980–1990.

Those two periods cannot be compared directly as an observed-versus- simulated calibration series.

Future formal calibration should reconstruct daily historical climate forcing for the period of the original river-flow observations and run the same watershed and HRU configuration for the matching historical period.

View the SWAT calibration and verification framework

Present interpretation

What the First SWAT Simulations Show

The first two Hare River SWAT simulations provide a coherent preliminary picture of the watershed's hydrological and sediment behaviour.

  • The model successfully represents continuous daily watershed behaviour over the 2020–2025 period.
  • Simulation 1 and Simulation 2 produce very similar overall water-balance results.
  • Surface runoff and subsurface flow both make important contributions to the Hare River.
  • Groundwater return flow forms a substantial part of simulated streamflow.
  • Strong seasonal hydrological response occurs particularly during April and again during October–November.
  • The largest daily outlet flow identified to date is 211.6 m³/s on 15 April 2024.
  • Upland sediment production is strongly spatially variable.
  • Small bare-ground HRUs produce disproportionately large simulated erosion rates.
  • SWAT indicates strong sediment deposition within the river network.
  • Current field evidence at the Hare diversion weir independently confirms that substantial sediment deposition is occurring at the headworks.
Present conclusion: the model is sufficiently developed to support preliminary watershed interpretation and engineering investigation. Formal hydrological and sediment calibration remain future stages before the numerical outputs are treated as fully validated predictions.
SWAT modelling sequence

From Watershed Data to Engineering Interpretation

DEM + Land Use + Soil + Slope
↓
17 Subbasins + HRUs
↓
Daily Climate 2020–2025
↓
Continuous SWAT Simulation
↓
Water Balance + Streamflow + Sediment
↓
Field Verification
↓
Hare Headworks Assessment

SWAT technical record

Related SWAT Documentation