River Health Analysis Tool

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River Parameters

Discharge i

BOD at 20°C (mg/L) i

Dissolved Oxygen (mg/L) i

Temperature (°C) i

🏭 Pollution Sources

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Environmental Constants

Stream Velocity (m/s) i

Deoxygenation K at 20°C (base e) i

Reoxygenation R at 20°C (base e) i

Temperature Coefficient for K i

Temperature Coefficient for R i

📋 Saturation DO Reference Table (Editable)

Temp (°C)

18

20

22

23

24

25

26

DO (mg/L)

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Frequently Asked Questions

1. What is the Streeter-Phelps Model primarily used for?

It predicts Dissolved Oxygen (DO) concentration in a river after a point source of organic pollution.

2. What is BOD and why is it important?

Biochemical Oxygen Demand – oxygen consumed by microorganisms decomposing organic matter; it represents the pollution load.

3. What are the two main opposing processes?

Deoxygenation (BOD decay) and Reoxygenation (atmospheric oxygen transfer).

4. What is the Critical Point?

Location where DO reaches its minimum value and oxygen deficit is maximum.

5. What does the Deoxygenation Rate Constant (K) represent?

Rate of oxygen consumption by bacteria; units day⁻¹.

6. What does the Reoxygenation Rate Constant (R) represent?

Rate of oxygen absorption from the atmosphere; influenced by turbulence.

7. What is the Self-Purification Factor (Fₛ)?

Ratio R/K – higher means faster recovery.

8. How does temperature affect the sag curve?

Higher temperature increases both K and R, usually lowering critical DO and moving it closer.

9. What is DO Saturation (Cₛ)?

Maximum oxygen water can hold at given temperature; colder water holds more.

10. What is the Initial Deficit (D₀)?

Cₛ − DOₘᵢₓ after mixing.

11. What is Ultimate BOD (L₀)?

Total oxygen eventually consumed; derived from BOD₅.

12. Why is critical DO important?

It is the lowest oxygen level, used to determine needed treatment to protect aquatic life.

13. What DO is required for sensitive cold‑water fish?

Generally 6.5 mg/L or higher.

14. What is Hypoxia?

DO below 2‑3 mg/L, causing fish kills.

15. How does velocity affect critical distance?

Higher velocity → longer critical distance for same critical time.

16. How does increasing BOD affect the curve?

Increases initial ultimate BOD, leading to greater deficit and lower critical DO.

17. What if R = K?

Equation for t_c is undefined; deficit approaches D₀ until BOD exhausted.

18. Relation between t_c and X_c?

X_c = v × t_c (velocity × time).

19. How to adjust for temperature?

Use temperature correction factors: K_T = K₂₀·θ^(T‑20).

20. What influences R?

Turbulence, depth, velocity – shallower, faster streams have higher R.

21. What does 72.6% saturation imply?

Water is under‑saturated; initial deficit makes river more vulnerable.

22. How is oxygen deficit percentage calculated?

(Cₛ − DOₘᵢₓ)/Cₛ × 100%.

23. What does pollution load (kg/s) tell?

Mass rate of ultimate BOD entering the river; high value demands strict control.

24. Meaning of dilution ratio 2.5:1?

For every 1 part waste, only 2.5 parts clean water – limited dilution capacity.

25. What does N/A recovery distance mean?

River never reaches 95% saturation within modeled reach; severe impairment.

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Model Assumptions & Limitations

🌊 Hydrodynamic Assumptions

Plug flow (no dispersion) High Impact
Constant velocity throughout reach
Steady‑state flow
One‑dimensional flow
Instantaneous complete mixing at discharge

🧪 Chemical & Biological Assumptions

Only carbonaceous BOD High Impact
No sediment oxygen demand
No photosynthesis/respiration Medium Impact
First‑order decay with constant rate
No BOD settling
No nutrient limitations
No toxic inhibition

🌡️ Temperature Assumptions

Constant mixed temperature downstream
Constant θ values
Linear interpolation of saturation table (18‑26°C)
No altitude correction (sea level assumed) Medium Impact

💨 Reaeration Assumptions

Constant R throughout reach High Impact
No channel geometry effects
No wind or surface films
Linear deficit model

🏭 Pollution Source Assumptions

Only point sources (no non‑point) High Impact
Continuous, constant discharge
No tributaries or withdrawals
No groundwater seepage

📊 Calculation Assumptions

BOD₅ → L₀ uses standard K (may vary)
95% recovery threshold arbitrary Low Impact
Max DO drop relative to initial river DO
No uncertainty analysis
Generic textbook coefficients High Impact

🚫 Excluded Factors

pH, heavy metals, pathogens
Nutrients/eutrophication
Salinity effects
Dams, waterfalls
Aquatic habitat structure

Critical Time i

–

days

Critical Distance i

–

km

Critical DO i

–

mg/L

Max DO Drop in River i

–

% drop

📐 Spot Check at Distance

Distance (km)

Enter a distance along the river and click Inspect Point to retrieve the exact BOD and DO values at that location.

🌊 River Health Analysis Tool