🌾 SwaNET · Quick Tutorial 13 of 19

LOADEST Tool for Pollutant Loads

Estimate constituent loads (nitrogen, phosphorus, metals) in streams and rivers using the USGS LOAD Estimator integrated directly into SwaNET.

SwaNET Tutorial 13Prereq: Loaded & Run SwaNET Model7 min read

Key Concepts

WhatUSGS LOADEST program integrated into SwaNET
InputFlow + concentration calibration data
OutputPredicted constituent loads over time
BonusOutput file uploads directly to SwaNET for calibration

○Overview

The SwaNET LOADEST tool is the integration of the USGS LOAD Estimator (LOADEST) program into the SwaNET modeling platform. LOADEST estimates constituent loads — such as nitrogen, phosphorus, and metals — in streams and rivers using measured flow and concentration data.

For detailed documentation, visit the USGS LOADEST site.

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Prerequisites: Load a SwaNET model before opening the LOADEST tool. If extracting flow from SWAT output, run the SWAT simulation first.

Access the Tool

Click Model Calibration → LOADEST tool at the top of the interface.

1Calibration Data

LOADEST requires paired flow and constituent concentration data for calibration. You upload or select a concentration data file; flow can come from the same file or from SWAT output.

Upload or Select a File

  1. New file: Check the box next to "Import" under Calibration data, click Import, browse to the file, and click Open.
  2. Existing file: Click Use Uploaded File, then select from the list of previously uploaded files.

Required Calibration File Format

CSV with four columns in this exact order. Headers can be any text.

calibration_data.csv
Date,Time,FLOW,CONC
1978/12/19,10:00,5700,0.04
1979/03/01,12:30,78200,0.03
1979/03/19,12:30,16600,0.02
1979/04/26,13:00,10100,<0.0100
1979/05/23,10:45,9960,<0.0100
1979/06/05,10:30,33900,0.01
ColumnFormatNotes
DateYYYY/MM/DDRequired format
TimeHH:MM24-hour clock
FlowAny numericSelect unit in the interface
ConcentrationNumeric or censorede.g., 0.5 or <0.1

Configure Calibration Options

  1. Enter a constituent name (e.g., Nitrogen) and select the unit (e.g., mg/L).
  2. Choose a flow source: select "Data file contains flow" and choose the unit, or select "Get flow from SWAT" and choose a subbasin.
  3. Click Next to proceed to the prediction interface.
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Tip: Even if your data file contains flow, you can replace it with SWAT model output for consistency with your simulation.

2Prediction Flow Data

The prediction file provides date, time, and flow for each time step where loads should be estimated. You can upload your own file or extract flow directly from SWAT output.

Option A — From a Data File

  1. Ensure Get flow from data file is checked.
  2. Upload or select a prediction flow file (same import process as calibration).
prediction_flow.csv
Date,Time,Flow
1980/01/01,12:00,14700
1980/01/02,12:00,13400
1980/01/03,12:00,12500
1980/01/04,12:00,11600
1980/01/05,12:00,11100

Format: three columns — Date (YYYY/MM/DD), Time (HH:MM), Flow (any numeric). Headers can be any text.

Option B — From SWAT Output

  1. Check Get flow from SWAT.
  2. Set the start and end dates for prediction (defaults to the full SWAT simulation period).
  3. Select the subbasin from which to extract prediction flow.

3Run LOADEST

  1. Select the output load unit (e.g., kg/day).
  2. Choose a prediction model. If you're unsure, select Auto select — LOADEST will automatically choose the best-fit model.
  3. Click Run LOADEST. The tool runs and results are displayed.

4View &amp; Export Results

Once complete, a prediction plot shows estimated constituent load over time (Y-axis) against date (X-axis). Previously run results can be reloaded via the Load latest results button on the main LOADEST interface.

  1. Change plot type: Select Prediction, Calibration, or Residual from the dropdown, then click Update plot.
  2. Download plot: Click Download image under "Download current image."
  3. Download data: Click Download file under "Download prediction file."

Output File Format

loadest_output.csv
Nitrogen(kg/day) data       ← Line 1: Header
1991,1,1,0                  ← Line 2: Start date (YYYY,M,D,H)
1                           ← Line 3: Multiplication factor
0,12.566                     ← Line 4+: Day offset, value
1,12.153
2,11.748
3,11.354
4,10.965
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Direct upload: This output file can be uploaded directly to SwaNET for manual or auto calibration — no reformatting needed.