Suspended-sediment concentrations at Phase II stream sites ranged from 1 to 273 mg/L, with a median of 15 mg/L. Jewel Creek had the highest median concentration (28 mg/L); at the remaining sites, the median ranged from 4.0 to 25.5 mg/L. The maximum suspended-sediment concentration, 273 mg/L, was measured in Oak Creek (fig. 22). Variations in land use did not correlate appreciably with differences in suspended-sediment concentrations.

Figure 22. Distribution of suspended-sediment concentrations, by site, in the Milwaukee Metropolitan Sewerage District planning area, Wis. Site abbreviations listed in table 1.

The median suspended-sediment concentration during high flow (26 mg/L) was higher than that during low flow (9 mg/L). Spring had the highest median concentration (20.5 mg/L); variability was similar among all seasons. The highest median concentration (39 mg/L) was observed during spring high flow (fig. 23A–C).

Figure 23. Distributions of suspended-sediment concentrations for stream and harbor samples, Milwaukee Metropolitan Sewerage District planning area, Wis. Stream sample distributions are grouped by flow (A), season (B), and flow and season combined (C). Harbor-sample distributions are grouped by season only (D) (no harbor samples were collected in winter).

Data were available for Phase I and Phase II suspended-sediment concentration comparisons at 11 sites (appendix 5). Suspended-sediment concentrations decreased from Phase I to Phase II at all sites, with percent differences ranging from -28 to -97 percent. The greatest decreases were observed at Kinnickinnic River (-97 percent), Underwood Creek (-97 percent), Honey Creek (-95 percent), and Root River at Grange Avenue (-93 percent).

Median suspended-sediment concentrations for harbor samples ranged from 1 to 45 mg/L. The overall median for harbor samples (2 mg/L) was lower than that for stream samples (15 mg/L). Inner-harbor sites had higher median concentrations (2–6.5 mg/L) than outer-harbor sites (1–2 mg/L). Harbor samples had the highest median concentration and greatest variability during spring (3.5 mg/L) (fig. 23D).

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Loads, Yields, and Volumetrically Weighted Concentrations of Suspended Sediment

Suspended-sediment loads for June through September 2004 ranged from 2,060 tons at Kinnickinnic River to 9,380 tons at Milwaukee River at Milwaukee (table 16). VW suspended-sediment concentrations ranged from 28 mg/L at Milwaukee River near Cedarburg to 227 mg/L at Kinnickinnic River. In water year 2005, the suspended-sediment load ranged from 2,380 tons at Kinnickinnic River to 8,340 tons at Milwaukee River near Cedarburg. VW suspended-sediment concentrations ranged from 23 mg/L at Milwaukee River at Milwaukee to 140 mg/L at Kinnickinnic River.

Table 16. Annual suspended-sediment load and yield, average daily sediment yield, total water flow, and volumetrically weighted sediment concentrations for four Phase II sites in the Milwaukee Metropolitan Sewerage District planning area, Wis.

[tons/mi², tons per square mile; tons/mi²/d, tons per square mile per day; ft³/s, cubic foot per second; mg/L, milligram per liter; VW, volumetrically weighted; --, no data; values in bold are for complete water years]

Combined averages of average daily sediment yields from June through September 2004 and water year 2005 were compared to combined average yields from available historical data. Menomonee River at Wauwatosa indicated the largest decrease, with average yields decreasing 50 percent. Milwaukee River at Milwaukee and Kinnickinnic River indicated comparatively moderate decreases (36 and 29 percent, respectively). Milwaukee River near Cedarburg indicated no change in average daily sediment yields.

Yields from water year 2005 ranged from 11.9 tons/mi² at Milwaukee River at Milwaukee to 127 tons/mi² at Kinnickinnic River (table 16). The median yield for the Southern Wisconsin Till Plains Ecoregion for rural sites was 32.4 tons/mi², and the range was 4.4 to 1,710 tons/mi² (Corsi and others, 1997). Yields from the two predominantly rural drainage basins (Milwaukee River near Cedarburg and Milwaukee River at Milwaukee) are within this range but near the minimum yield. The median yield for urban sites in the Southern Wisconsin Till Plains Ecoregion ranged from 17 to 451 tons/mi², and the median was 130 tons/mi² (Corsi and others, 1997). Yields from the two predominantly urban drainage basins (Menomonee River at Wauwatosa and Kinnickinnic River) were 29.7 tons/mi² and 127 tons/mi², respectively (table 13). These yields were within the Ecoregion range for urban sites, with the Kinnickinnic River site close to the median.

VW sediment concentrations for averages of water years 2004 and 2005 ranged from 27 mg/L at Milwaukee River at Milwaukee to 184 mg/L at Kinnickinnic River (table 16). The sediment concentrations were within the range of sediment concentrations previously found at sites within the MMSD planning area (Schneider and others, 2004). When compared to combined averages of available historical data, Menomonee River at Wauwatosa had the greatest decrease in VW sediment concentration with a 55-percent decrease. The next greatest decrease was observed at Milwaukee River at Milwaukee, with a 52-percent decrease. Decreases at Kinnickinnic River and Milwaukee River near Cedarburg were more moderate, with decreases of 25 and 26 percent, respectively.

Suspended-sediment loads indicated a seasonal pattern at Milwaukee River near Cedarburg and Milwaukee River at Milwaukee in water year 2005, with higher loads generally being recorded from February through May (table 17). A seasonal pattern was also observed at Menomonee River at Wauwatosa with generally elevated levels during these same months, and highest loads were recorded in January. No seasonal response in suspended sediment loads was observed at Kinnickinnic River during water year 2005. The greatest monthly loads of suspended sediment for data collected in 2004 were recorded in June at Milwaukee River near Cedarburg and Milwaukee River at Milwaukee, in July at Menomonee River at Wauwatosa, and in August at Kinnickinnic River.

Table 17. Monthly and annual suspended-sediment loads for four Phase II sites in the Milwaukee Metropolitan Sewerage District planning area, Wis., for water years 2004 and 2005.

[WY, water year]

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