Comparison of infiltration models with regard to design of rectangular infiltration trenches

Figures & data

Table 1. Comparison of design criteria for infiltration trenches of rectangular cross-section. h_max: maximum water depth, H: separation between trench bottom and GW level.

Item	Guidelines
	BRE (Building Research Establishment) (2003)	DWA (Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall) (2005)
Return period of design storm (rain)		10 years
Design rain duration, dr	Estimated as a critical value within the range 10–600 min
Max. catchment area	No limit	200 ha
Max. concentration time	No limit	15 min
Infiltration area, As	50% of area of effective walls (excluding bottom)	Bottom area + 50% of area of effective walls
Saturated hydraulic conductivity of the native soil, Ks	No limits	Ks = 1 × 10^−6 to 1 × 10^−3 m s^−1
Vertical hydraulic gradient, Iz	Iz = 1	Iz = (0.5 hmax + H)/H
Infiltration rate, fc	Based on percolation test in a trial pit	0.5 Iz Ks
Filling time, tf	Rainfall duration, dr
Emptying time, te	Max. 24 h to empty upper half volume	Max. 24 h to empty the whole volume

Figure 1. Rectangular cross-section of infiltration trench of width b and length L showing the infiltration concept of Type II at two phases: 1 – the left half (filling), and 2 – the right half (emptying).

Figure 2. Scheme showing the infiltration concept of Type IIIa and distribution of infiltration rate f_c along the wetted perimeter of a rectangular trench.

Figure 3. Distribution of infiltration velocity w and mean infiltration rates f_c (Type IIIb).

Figure 4. Sketch of the infiltration trench in the 2D numerical model.

Table 2. Physical parameters of soils in the infiltration trench.

Soil type	θr (-)	θS (-)	α (cm^−1)	n (-)	Ks (cm s^−1)	l (-)
Sandy loam	0.046	0.356	0.0364	1.4532	0.00046	0.5
Gravel	0.05	0.35	1.75	2.8	0.1	0.5

Figure 5. Comparison of results obtained using different infiltration concepts with field data.

Figure 6. Velocity distribution (cm min⁻¹) at the end of water inflow to the trench at initial soil moisture: (a) θ = 0.2 and (b) θ = 0.35.

Figure 7. Relative mean infiltration rates f_c/K_s versus relative water depth h/b: according to DWA (Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall) (2005). Dotted line: I_z = 1, dashed line: Type II, solid line: Type IIIb.

BRE (Building Research Establishment), 2003. Soakaway design. Digest 365. Watford, UK: BRE.

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DWA (Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall), 2005. Standard DWA-A 138E. Planning, construction and operation of facilities for the percolation of precipitation water. Hennef: German Association for Water, Wastewater and Waste.

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