The short-term influence of cumulative, sequential rainfall-runoff flows on sediment retention and transport in selected SuDS devices

Figures & data

Figure 1. Schematic diagrams of established, field monitored SuDS. A linear wetland, within the Scottish contest, is a large swale densely vegetated with wetland plants but without permanent ponding areas provided within a wetland or wetland flow depth. Note that sampling intern deposition across the large pond was not possible due to pond depth and health and safety regulations. The large pond deposition is estimated using sample points 1 and 4 (in the pond), 5, within the outlet flow path and known inflows (inlet, samples 2 and 3).

Figure 2. SuDS device REO tagged sediment retention curves (from mass balance calculations and field monitoring) and preferential fortnightly deposition locations (as a representation of total tagged sediment deposition).

Table

SuDS device	Average flow depth over monitoring period	Indicative area weighting of SuDS device by monitoring location (m2)^a
Wetland	1.0 m (ponding area) 0.3 m (vegetated shallow areas)	Sample 1	Sample 2	Sample 3	Sample 4
		34 m^2	165 m^2	238 m^2	173 m^2
Linear wetland	0.5 m (event flow depth average)	Sample 1	Sample 2	Sample 3
		6 m^2	7 m^2	5 m^2
Short Swale	0.3 m (event flow depth average)	Sample 1	Sample 2
		3 m^2	3 m^2
Long Swale	0.4 m (event flow depth average)	Sample 1	Sample 2
		7 m^2	11 m^2
Large Pond	+1.0 m	Sample 1	Sample 2	Sample 3	Sample 4	Sample 5
		-	-	-	16,240 m^2	5 m^2
Small Pond	0.4 m (0.6 m if silty sludge on pond base is included)	Sample 1 (back flow area)	Inlet sample	Sample 3	Sample 4 (vegetated high flow area)	Sample 5	Outlet sample US
		300 m^2	400 m^2	700 m^2	330 m^2	330 m^2	340 m^2
Small pond continued		Outlet sample DS		Upstream receiving watercourse sample		Downstream receiving watercourse sample
		165 m^2		50 m^2		50 m^2

^a Indicative areas reflect the spatial extent of each SuDS device represented by a sediment deposition and suspension monitoring location. It is acknowledged that this presents an indication not definitive quantification but due to the nature of the experiments (ongoing movement of sediment over multiple, consecutive rainfall-runoff events) sampling of the total SuDS deposition and suspended sediment was not possible.

Table

Rare Earth Element	Atomic number	Orbitals/Electronic configur-ation	Orbital states	Atomic Radius (pm)	Ionic Radius (pm)	Atomic Mass (u)	Boiling point (k)	Melting point (K)	Density (kg/m3 at 293K)	Isotopic half-life (yrs)
Ho	67	4f^116s^2	+3	176	90	164.9	2968	1747	8795	‘stable’
Pr	59	4f^36s^2	+3, +4	182	99	140.9	3785	1204	6773	‘stable’
Sm	62	4f^66s^2	+3	181	97	114.9	3000	1441	7220	1.06 × 10^11
Nd	60	4f^46s^2	+2, +3, +4	181	98	144.9	3341	1294	7007	2.1 × 10^15
Gd	64	4f^75d^16s^2	+3	179	94	157.3	3539	1586	7900	1.1 × 10^14
Yb	70	4f^146s^2	+2, +3	193	87	173	1466	1097	6965	‘stable’
Er	68	4f^126s^2	+3	175	89	167.3	3136	1802	9066	‘stable’
Dy	66	4f^106s^2	+3, +4	177	91	162.5	2835	1685	8550	2 × 10^14
Tb	65	4f^96s^2	+3, +4	178	92	158.9	3396	1629	8229	‘stable’
Y	39	4d^15s^2	+3	180		88.9	3911	1795	4469	‘stable’
La	57	5d^16s^2	+3	187	103	138.9	3730	1194	6145	1.05 × 10^11
Ce	58	4f^26s^2	+3, +4	182	101	140.1	3699	1204	6773	‘stable’

Note: ‘stable’ is geochemically defined as theoretically capable of spontaneous fission, thus not considered to decay.

Table

		Limits of detection
Element	Analytical mass	Minimum (part per trillion, ppt)	Maximum (parts per billion, ppb)	Variance or errors in analysis (RSD%)
Ho	^165Ho	0.02	100	0.56–1.46%
Pr	^141Pr	0.008	100	0.69–1.16%
Sm	^147Sm	0.07	100	0.7–1.72%
Nd	^145Nd	0.03	100	0.77–1.1%
Gd	^157Gd	0.03	100	0.89–1.23%
Yb	^173Yb	0.06	100	0.86–1.43%
Er	^167Er	0.08	100	0.44–1.11%
Dy	^163Dy	0.09	100	0.39–1.22%
Tb	^159Tb	0.01	100	0.38–1.45%
Y	^89Y	0.01	100	0.61–1.41%
La	^139La	0.01	100	0.77–1.31%
Ce	^140Ce	0.01	100	0.63–1.16%

Table

	Rainfall since last sample					Most recent event
	Rainfall (mm)	Number of rainfall events	Average intensity (mm/hr)	ADD during sample period (hrs)	Dry period prior to sample (hrs)	Intensity (mm/hr)	Rainfall duration (hrs)	Rainfall (mm)
week 0	11.4	5	0.43	0	4	1.7	4	7
week 2	25	10	1.02	216	2	2.2	2	4.4
week 4	17.4	22	0.43	264	0	12	0.03	0.4
week 6	6.4	12	0.77	312	1.5	0.7	0.9	0.6
week 8	9.6	19	1.89	240	5	12	0.03	0.4
week 10	56.6	15	3.94	264	8	12	0.03	0.4
week 12	66.8	24	1.77	240	7.5	4.3	1.3	5.4
week 14	51.6	15	1.9	96	0	1.6	1.9	3
week 16	11.2	4	1.45	144	47	12	0.03	0.4
week 18	51.4	8	2.1	264	26.5	12	0.03	0.4
week 20	0.4	1	12	120	7.5	12	0.03	0.4
week 22	51.4	10	2.56	240	90.5	12	0.03	0.4
week 24	19	7	1.46	96	1	1.2	9	10.4
week 26	98	8	1.96	96	2.5	1.8	23	42
week 28	65.6	11	2.47	240	16.5	9.8	0.4	3.6
week 30	0	0	0	72	88.5	0	0	0
week 32	6.8	4	1.48	288	43.5	0.6	3	1.8
week 34	18	5	0.26	168	41.5	30	0.03	1
week 36	5.6	3	0.7	288	41.5	1.4	0.8	1.2
week 38	85.2	7	1.43	288	42.5	1.1	6	6.8
week 40	38.2	19	1.61	144	1.5	12	0.03	0.4
week 42	1.6	4	12	288	39	12	0.03	0.4
week 44	15	9	1.76	264	5.5	1.1	4	4.4
week 46	90.2	8	2.42	216	15	2.1	0.6	1.2
week 48	46.8	13	1.59	264	4	2.7	1	2.8
week 50	85.6	22	1.93	192	2	3	2	5.4
week 52	39.4	13	1.62	264	31	7.2	0.1	0.6
Average	36.1	10	2.3	206	21	6.7	2.2	4.0
Minimum	0.0	0	0.0	0	0	0.0	0.0	0.0
Maximum	98.0	24	12.0	312	91	30.0	23.0	42.0

Table

	Rainfall since last sample					Most recent event
	Rainfall (mm)	Number of events	Average intensity (mm/hr)	ADD during sample period (hrs)	Dry period prior to sample (hrs)	Intensity (mm/hr)	Rainfall duration (hrs)	Rainfall (mm)
month 1	40	42	0.4	627	0	0.2	4	2.0
month 2	59.8	24	0.6	646	6	0.2	5	1.2
month 3	35.8	20	0.6	669	14	0.2	1	0.2
month 4	32	22	0.4	679	92	0.2	1	0.2
month 5	18.8	25	0.4	676	52	0.2	1	0.2
month 6	37.8	22	0.5	653	18	0.9	3	2.6
Average	37.4	26	0.5	658	30	0.3	3	1.1
Minimum	18.8	20	0.1	627	0	0.2	1	0.2
Maximum	59.8	42	2.25	679	92	0.9	5	2.6