Detention Pond Routing
Level-Pool / Storage-Indication Method
Peak Inflow
0.0 m³/s
Peak Outflow
(-0.0%) 0.0 m³/s
(-0.0%) 0.0 m³/s
Max WSEL
(Water Surface Elevation) 0.0 m
(Water Surface Elevation) 0.0 m
Max Storage Volume
0.0 m³
Inflow & Outflow Hydrographs vs WSEL
Stage-Storage Curve
Stage-Discharge Curve
Routing Time-Series Results
| Time (hr) |
Inflow (m³/s) |
Outflow (m³/s) |
Elevation (m) |
Storage (m³) |
|---|
Hydrologic Basis
1. Level-Pool Routing (Storage-Indication Method)
Level-pool routing assumes that the water surface in the reservoir remains perfectly horizontal during filling and emptying. The fundamental principle is the Conservation of Mass: Change in Storage = Inflow - Outflow.
$$\frac{I_1 + I_2}{2} - \frac{O_1 + O_2}{2} = \frac{S_2 - S_1}{\Delta t}$$
2. The Storage-Indication Equation
To solve the equation at each time step, all known variables (from time $t_1$ and inputs $I_2$) are grouped on the right side, and unknowns (at time $t_2$) are grouped on the left. This creates the "Storage Indication" parameter $2S/\Delta t + O$:
$$\left( \frac{2S_2}{\Delta t} + O_2 \right) = (I_1 + I_2) + \left( \frac{2S_1}{\Delta t} - O_1 \right)$$
At each time step, the right side is calculated, and the value is used to interpolate $O_2$, $S_2$, and the new Elevation $E_2$ from a pre-computed routing curve.
3. Volume Approximation (Conic Method)
When providing surface areas at specific elevations, the incremental volume between two elevations is computed using the Conic Approximation formula, which is more accurate than the Average End Area method for typical pond shapes:
$$\Delta V = \frac{\Delta E}{3} \left( A_1 + A_2 + \sqrt{A_1 \cdot A_2} \right)$$
References & Sources
- USDA Natural Resources Conservation Service (NRCS). (2007). National Engineering Handbook (NEH), Part 630: Hydrology. Chapter 17: Flood Routing. (Comprehensive guide on the Storage-Indication method). [View NEH Chapter 17]
- Chow, V. T., Maidment, D. R., & Mays, L. W. (1988). Applied Hydrology. McGraw-Hill. (Foundational text for level-pool reservoir routing algorithms and numerical methods). [Search on Google Scholar]
- Federal Highway Administration (FHWA). (2009). Urban Drainage Design Manual (HEC-22). Chapter 8: Detention and Retention Facilities. [Download HEC-22 PDF]
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