Appendix A. Regression Models for Relation of Turbidity and Suspended-Sediment Concentration in the North Santiam River Basin

As explained in section “Data Analysis”, the regression models required annual updating and verification. Bragg and others (2007) developed a single model for each monitoring station with samples collected during water years 1999–2004 to estimate suspended-sediment concentration from turbidity for those 5 years. The newly published method for updating the regression models (Rasmussen and others, 2009) involved adding the samples collected during each subsequent water year to the model calibration dataset and repeating the regression analysis with the new dataset. If the new model showed no significant change from the old model, the new model was used to estimate the continuous SSC record for the most recent water year. The regression models used at each monitoring station for each water year that suspended-sediment loads were computed are shown in table A1.

Table A1.Regression model equations used at each monitoring station, North Santiam River basin, Oregon, water years 1999–2008.

[Station reference: Complete station names are shown in table 1 and locations are shown in figure 1. N, number of samples; R2, coefficient of determination; MSPE, model standard percent error; SSC, suspended-sediment concentration; T, turbidity]

Station reference	Regression model equation	Bias correction factor	N	R2	Upper MSPE	Lower MSPE
Water years 1999–2004
North Santiam	log10 SSC = 1.04 log10 T + 0.188	1.13	121	0.89	68.0	40.5
Breitenbush	log10 SSC = 1.08 log10 T + 0.183	1.18	80	0.92	71.3	41.6
French	log10 SSC = 1.01 log10 T - 0.0127	1.28	34	0.82	105	51.3
Blowout	log10 SSC = 1.18 log10 T + 0.0683	1.16	118	0.93	62.3	38.4
Niagara	log10 SSC = 0.758 log10 T + 0.123	1.12	64	0.76	63.2	38.7
Little North	log10 SSC = 1.02 log10 T + 0.193	1.14	125	0.92	66.3	39.8
Mehama	log10 SSC = 0.916 log10 T + 0.170	1.17	131	0.86	78.6	44.0
Water year 2004 (Revised)
North Santiam (Precipitation-driven)	log10 SSC = 1.07 log10 T + 0.243	1.12	116	0.91	60.2	37.6
North Santiam (Meltwater-driven)	log10 SSC = 0.907 log10 T + 0.0651	1.04	32	0.95	31.0	23.6
Water year 2005
North Santiam (Precipitation-driven)	log10 SSC = 1.08 log10 T + 0.240	1.11	122	0.92	58.8	37.0
North Santiam (Meltwater-driven)	log10 SSC = 0.908 log10 T + 0.0690	1.03	35	0.95	30.0	23.1
Breitenbush	log10 SSC = 1.03 log10 T + 0.220	1.08	92	0.96	48.8	32.8
Blowout	log10 SSC = 1.08 log10 T + 0.150	1.12	127	0.93	58.4	36.9
Niagara	log10 SSC = 0.718 log10 T + 0.156	1.11	62	0.79	59.3	37.2
Little North	log10 SSC = 1.03 log10 T + 0.196	1.12	123	0.91	61.9	38.2
Mehama	log10 SSC = 0.931 log10 T + 0.146	1.14	127	0.87	71.4	41.6
Water year 2006
North Santiam (Precipitation-driven)	log10 SSC = 1.10 log10 T + 0.233	1.10	136	0.94	56.8	36.2
North Santiam (Meltwater-driven)	log10 SSC = 0.908 log10 T + 0.0690	1.03	35	0.95	30.0	23.1
Breitenbush	log10 SSC = 1.05 log10 T + 0.218	1.09	103	0.96	50.3	33.4
Blowout	log10 SSC = 1.08 log10 T + 0.143	1.11	150	0.94	56.0	35.9
Niagara	log10 SSC = 0.729 log10 T + 0.153	1.10	73	0.83	53.8	35.0
Rock	log10 SSC = 1.05 log10 T + 0.241	1.06	20	0.94	48.2	32.5
Little North	log10 SSC = 1.03 log10 T + 0.195	1.12	126	0.92	61.1	37.9
Mehama	log10 SSC = 0.937 log10 T + 0.152	1.15	133	0.87	72.5	42.0
Water year 2007
North Santiam (Precipitation-driven)	log10 SSC = 1.12 log10 T + 0.222	1.12	148	0.94	60.6	37.7
North Santiam (Meltwater-driven)	log10 SSC = 0.898 log10 T + 0.0772	1.03	40	0.95	28.8	22.4
Breitenbush	log10 SSC = 1.07 log10 T + 0.213	1.09	115	0.96	50.0	33.3
Blowout	log10 SSC = 1.09 log10 T + 0.138	1.10	165	0.95	54.4	35.2
Niagara	log10 SSC = 0.737 log10 T + 0.150	1.10	76	0.84	53.7	35.0
Rock	log10 SSC = 1.05 log10 T + 0.241	1.06	25	0.95	43.8	30.5
Little North	log10 SSC = 1.03 log10 T + 0.196	1.12	129	0.92	60.3	37.6
Mehama	log10 SSC = 0.943 log10 T + 0.148	1.14	136	0.88	71.8	41.8
Water year 2008
North Santiam (Precipitation-driven)	log10 SSC = 1.12 log10 T + 0.224	1.12	151	0.95	60.0	37.5
North Santiam (Meltwater-driven)	log10 SSC = 0.898 log10 T + 0.0772	1.03	40	0.95	28.8	22.4
Breitenbush	log10 SSC = 1.06 log10 T + 0.215	1.09	119	0.96	50.7	33.6
Blowout	log10 SSC = 1.09 log10 T + 0.140	1.10	169	0.95	54.7	35.3
Niagara	log10 SSC = 0.727 log10 T + 0.163	1.10	78	0.84	54.1	35.1
Rock	log10 SSC = 1.05 log10 T + 0.243	1.06	27	0.94	45.3	31.2
Little North	log10 SSC = 1.02 log10 T + 0.209	1.12	131	0.92	60.9	37.8
Mehama	log10 SSC = 0.931 log10 T + 0.164	1.15	137	0.87	73.2	42.2