⏱️ Time of Concentration Calculator "BETA" WA-726-1 - Stormwater and Subsoil Drainage Systems (Volume) - Abu Dhabi Design Manual
Rural (kinematic wave + IDF) · Urban (entry time + pipe travel) · design storm multipliers
📋 Select catchment priority (Table 3-3):
⏱️ time of concentration (Tc)
—
minutes
📅 design storm duration (Tc × multiplier)
—
minutes
📋 Catchment Summary
| ID |
# |
Type |
Parameters |
Priority |
Tc (min) |
Design Dur. (min) |
Action |
Plan view · longest flow path L
Cross‑section · slope S, pipe parameters
3D view · overland & pipe flow
🌿 rural · kinematic wave + IDF (WA‑726‑1 §3.2.3)
Tc = 0.12 · n0.6 · L0.6 / ( S0.3 · i0.4 ) [hr] with i = α / (Tcβ)
L (m) · n · S (m/m)
α,β from IDF (zone/return period)
⏳ select inputs
📘 Manning's n values (WA‑726‑1 references)
| Surface / Material | Manning's n | Source / Remarks |
|---|
| Rural undeveloped (Abu Dhabi) | 0.020 – 0.035 | §3.2.3 – kinematic wave |
| Concrete pipe (trowelled finish) | 0.012 | Table 4‑1 (Colebrook‑White equivalent) |
| Concrete pipe (unlined, Al Ain) | 0.013 | Table 4‑1 |
| uPVC / HDPE pipes | 0.011 – 0.012 | Table 4‑1 |
| GRP pipes | 0.011 – 0.015 | Table 4‑1 (depends on roughness) |
| Concrete gutter (trowelled) | 0.012 | Table A3‑1 |
| Asphalt pavement (smooth) | 0.013 | Table A3‑1 |
| Asphalt pavement (rough) | 0.016 | Table A3‑1 |
| Concrete pavement (float finish) | 0.014 | Table A3‑1 |
| Concrete pavement (broom finish) | 0.016 | Table A3‑1 |
| Earth channel (bare) | 0.020 – 0.030 | Table A5‑4 (clay, sand, gravel) |
| Rock riprap lined channel | 0.035 | Table A5‑4 |
| Grass-lined channel | 0.030 – 0.040 | approximate |
Note: For urban overland flow, the manual uses velocity coefficients (Figure 3‑1) instead of Manning's n. Pipe Manning values are for full‑bore flow.
| Priority | Catchment type | Tc multiplier |
|---|
| 1 | Major roads, underpasses, airports, seaports | Tc |
| 2 | High density (≥50% impervious) | 2·Tc |
| 3 | Low density (≤50% impervious) | 3·Tc |
| 4 | Industrial sectors* | 5·Tc |
| 5 | Open areas, parks | 12·Tc |