Effect of seasonal flushing on nutrient export characteristics of an urbanizing, remote, ungauged coastal catchment

Figures & data

Figure 1. Broome coastal sub-catchments and Roebuck Bay.

Figure 2. (a) Mean monthly rainfall and mean number of days of rain ≥10 mm in Broome for the periods 1939–2012 and December 2011–March 2012 (BOM 2013). Grey areas show the 2011/12 wet season (study period), which spans from January to March. (b) Rainfall, rainfall intensity and antecedent dry period. (c) Calculated runoff volume from sub-catchments for the 2011/12 wet season.

Table 1. Characteristics of urbanizing sub-catchments in Broome town.

Sub-catchment ID	Catchment area (ha)	Impervious %	Seasonal runoff coefficient	Slope	Land-use code
APT	184.26	40.13	0.63	0.008	MDR+IND
DMC	12.82	36.01	0.46	0.02	MDR
HGS	10.33	25.98	0.44	0.059	MDR
MBB	30.71	31.06	0.22	0.002	MDR
MTS	20.57	43.47	0.53	0.059	MDR
SVS	8.51	28.96	0.23	0.012	MDR
TB	53.87	32.88	0.55	0.01	MDR
GB	172.57	27.58	0.51	0.016	HDR+UDA
RBE	156.5	22.69	0.32	0.014	HDR+UDA
VN	67.89	20.68	0.11	0.017	LDR+CLL
NTE	29.39	13.23	0.42	0.007	CLL+UDA

Figure 3. Relationships between runoff, impervious percentage and rainfall intensity.

Figure 4. (a) Temporal variation of EMCs of TN, N-NH₄⁺, N-NO_x⁻, TP and P-PO₄³⁻ for the 2011/12 wet season from the 11 sub-catchments. (b) SMFF ratios for TN, NH₄⁺, N-NO_x⁻, TP and P-PO₄³⁻ against cumulative runoff volume for the study period for all sub-catchments. In (b), the dashed line at 1.0 represents the SMFF where the nutrient loadings are uniform throughout the wet season (i.e. no seasonal first flush). Values >1 indicate the seasonal first flush during the early part of the wet season.

Figure 5. Bi-plot for the first two principal components with nutrient, catchment and hydrological variables and their correlations with sub-catchments.

Figure 6. Nutrient export coefficients from Broome coastal sub-catchments.

Table 2. Typical/median nutrient export coefficients for different catchments in different climate conditions (Beaulac and Reckhow 1982, Young et al. 1996, Taylor et al. 2005).

	TP export coefficient (kg ha^−1 year^−1)	TN export coefficient (kg ha^−1 year^−1)
Urban catchment	Typical/Median	Typical/Median	Catchment size (ha)	Climate
Queensland, Australia	1	6.6	10^2–10^3	Subtropical
Southwest Australia	0.4	2.5	10^1–10^2	Mediterranean
Victoria, Australia	1.4	4.5	10^0–10^2	Temperate
North America	1.2	5.5
Broome, Western Australia	0.12	0.55	10^0–10^2	Subtropical

Figure 7. Hydrographs and pollutographs for representative sub-catchments from Old Broome Town (MTS) and Broome North (GB). Runoff volumes were converted to runoff depths in mm and nutrient concentrations were normalized by dividing a particular nutrient concentration at a time by the initial nutrient concentration at the start of the wet season. Time was normalized as 1 represents 180 min.

Figure 8. Framework for managing storm-water nutrients from an ungauged, remote, subtropical catchment.

Figure B1. Cumulative nutrient loading percentage curves for (a) TN, (b) NH4+, (c) N-NO_x⁻, (d) TP and (e) P-PO₄³⁻ against cumulative runoff volume percentages in the 11 sub-catchments. A seasonal first flush occurs if the data ascend above the dashed line, which represents uniform nutrient loading throughout the wet season.

Table A1. Manning’s n values for Broome drains in each sub-catchment. Values were compiled from the literature (French 1986, Streeter et al. 1987, FHWA 2011) and selected following the guide by Arcement and Schneider (1989).

Sub-catchment	n	Nature of the channel
APT	0.037	Clean, winding, some pools and shoals
DMC	0.013	Unfinished concrete
HGS	0.013	Finished concrete
MBB	0.030	Clean, straight, full stage, no rifts or deep pools, with more stones and weeds
MTS	0.028	Clean, straight, full stage, no rifts or deep pools
GB	0.048	Clean, winding, some pools and shoals with some weeds and more stones
NTE	0.025	Clean, straight, full stage, no rifts or deep pools
RBE	0.040	Clean, winding, some pools and shoals with some weeds and stones
SVS	0.025	Clean, straight, full stage, no rifts or deep pools
TB	0.048	Clean, winding, some pools and shoals with some weeds and more stones

Table C1. Correlation matrix for the parameters presented in the PCA bi-plot. Bold indicates significant values (except diagonal) at the level of significance α = 0.050 (two-tailed test).

	TNS	TPS	NH4S	NOxS	PO4S	SLP	A	IMP	ROC	TWWD	TNEC	TPEC
TNS	1
TPS	0.885	1
NH4S	0.706	0.521	1
NOxS	0.406	0.090	0.603	1
PO4S	0.891	0.945	0.512	0.274	1
SLP	0.491	0.615	0.067	−0.230	0.568	1
A	−0.506	−0.725	−0.162	0.004	−0.773	−0.384	1
IMP	−0.283	−0.070	−0.331	−0.505	−0.083	0.318	0.042	1
ROC	−0.339	−0.353	−0.323	−0.461	−0.418	0.305	0.406	0.694	1
TWWD	−0.652	−0.632	−0.562	−0.262	−0.624	−0.457	0.564	0.328	0.330	1
TNEC	0.284	0.359	0.112	−0.220	0.383	0.707	−0.202	0.651	0.495	−0.222	1
TPEC	0.297	0.297	0.019	−0.137	0.363	0.598	−0.187	0.668	0.550	−0.118	0.927	1

Bureau of Meteorology (BOM), 2013. Climate of Broome. Australian Government, Bureau of Meteorology. Available from: http://www.bom.gov.au/climate/averages/tables/cw_003003.shtml [ Accessed 12 November 2013].

 Google Scholar

Beaulac, M.N. and Reckhow, K.H., 1982. An examination of land-use nutrient export relationships 1. Journal of the American Water Resources Association, 18 (6), 1013–1024. doi:10.1111/jawr.1982.18.issue-6

 Google Scholar

Young, W.J., Marston, F.M., and Davis, J.R., 1996. Nutrient exports and land use in Australian catchments. Journal of Environmental Management, 47, 165–183. doi:10.1006/jema.1996.0043

 Web of Science ®Google Scholar

Taylor, G.D., et al., 2005. Nitrogen composition in urban runoff—implications for stormwater management. Water Research, 39 (10), 1982–1989. doi:10.1016/j.watres.2005.03.022

 PubMed Web of Science ®Google Scholar

French, R.H., 1986. Open-channel hydraulics (International Edition). Singapore: McGraw-Hill Book.

 Google Scholar

Streeter, V.L., Wylie, E.B., and Wylie, Z., 1987. Fluid mechanics. New York, NY: WCB/McGraw-Hill.

 Google Scholar

Federal Highway Administration (FHWA), 2011. Introduction to Highway Hydraulics; Drainage design charts and tables United States Department of Transportation. Available from: <http://www.fhwa.dot.gov/engineering/hydraulics/pubs/08090/appb.cfm> [Accessed 05 August 2013].

 Google Scholar

Arcement, G.J. and Schneider, V.R., 1989. Guide for selecting Manning’s roughness coefficients for natural channels and flood plains. United States Geological Survey water-supply paper 2339. Denver, CO: USGS.

 Google Scholar