Fig. 1.

Map of Tipton Creek, Iowa, and its watershed, with locations of gauging stations that monitored discharge and water quality from the watershed outlet (TC325), two tile-drained subbasins (TC240 and TC242), and a field runoff flume (TC101).

 


Fig. 2.

Rainfall amounts received on 10 to 11 Sept. 2006, with a map based on radar rainfall data showing relative distribution of rainfall across the Tipton Creek, Iowa, watershed, estimated based on methods described by Cruse et al. (2006)

 


Fig. 3.

Three-year record of total P concentrations observed during rainfall-runoff events at two tile outfalls (TC240 and TC242) and at the outlet (TC325), Tipton Creek, Iowa. Arrows indicate September 2006 event.

 


Fig. 4.

Left panel: Observed hydrograph records at the stream outlet (TC325), field runoff flume (TC101), and tile outfall (TC240) during the September 2006 rainfall-runoff event, Tipton Creek, Iowa. Right panel: The hydrograph at TC325 is shown and changes in discharge (Q) are interpreted and associated with major flow pathways.

 


Fig. 5.

Discharge rates (Q) and concentrations of total P, NO3–N, and E. coli during the observed September 2006 rainfall-runoff event at two tile outfalls, TC240 and TC242, Tipton Creek, Iowa. Note that the scale is linear for the nutrients, but that E. coli data are given on a (natural) log scale due to the large populations. mpn, most probable number.

 


Fig. 6.

Discharge rates (Q) and concentrations of total P, NO3–N, and E. coli during the observed September 2006 rainfall-runoff event at the field flume, TC101, Tipton Creek, Iowa. Note that the scale is linear for the nutrients, but that E. coli data are given on a (natural) log scale due to the large populations. mpn, most probable number.

 


Fig. 7.

Discharge rates (Q) and concentrations of total P, NO3–N, and E. coli during the observed September 2006 rainfall-runoff event at the watershed outlet, TC325, Tipton Creek, Iowa. Note that the scale is linear for the nutrients, but that E. coli data are given on a (natural) log scale due to the large populations. mpn, most probable number.

 


Fig. 8.

Hydrograph separation of total discharge (Q) into surface and subsurface-tile (Q (tile)) flow components at two tile outfalls (TC240 and TC242, top two panels), and into surface, tile-flow, and groundwater discharge (Q (groundwater)) components at the watershed outlet (TC325, lower panel), Tipton Creek, Iowa. Surface (overland) flows are the difference between Q and Q (tile)

 


Fig. 9.

Cumulative loads of (a) NO3–N, (b) total P, and (c) E. coli during the September 2006 rainfall-runoff event, Tipton Creek, Iowa, from the watershed outlet (TC325), two tile outfalls (TC240 and TC242), and a surface flume (TC101), expressed on a unit-area basis. cfu, colony-forming units.

 


Fig. 10.

Sediment concentration, estimated from relationship with turbidity, during the September 2006 rainfall-runoff event, Tipton Creek, Iowa, with relative proportion from bank sources, based on radionuclide separations.

 


Fig. 11.

Above: Sediment loading rates during the September 2006 rainfall-runoff event. Field (surface-soil) and channel sources, separated using radionuclide data, are plotted discretely. Below: Cumulative sediment loads during the event, with channel and field sources plotted additively.