USGS Scientific Investigations Report 2010–5016 Development of an Environmental Flow Framework for the McKenzie River Basin, Oregon

Table 20. Geomorphic characteristics of reaches in the McKenzie River basin, Oregon.

[Valley bottom width mapped from 10-m DEM and corresponds to Quaternary alluvium as mapped by Sherrod and Smith (2000), which forms Pleistocene terraces above the modern floodplain. Floodplain mapped from FEMA floodplain for Lane County; FEMA floodplain closely corresponds with the Holocene floodplain (map unit Qalc) as mapped by O’Connor and others (2001) for areas below Leaburg. Channel slope measured from 10 m DEM as change in elevation divided by length along the rasterized stream network. Sinuosity calculated as centerline length, as measured along the center of the 2005 active channel, divided by the valley length of the channel. Active channel (reach-average active channel) width in 2005 calculated for each reach from transects drawn orthogonal to the centerline at approximately 1 km intervals using the 2005 aerial photographs as a base image. Floodplain width index calculated as floodplain width divided by active channel width (similar to Grant and Swanson, 1995). Off-channel habitat index calculated as length of side-channels and alcoves (as mapped from 2005 aerial photographs) divided by floodplain length. Brief description: Channel morphology for reaches 1, 2, 4, and 5 from Minear (1994) and Stillwater Sciences (2006b), who described channel morphology using classification system presented by Montgomery and Buffington (1997). Abbreviations: ft, feet; mi, mile; m, meter; DEM, Digital Elevation Model; FEMA, Federal Emergency Management Agency]

Reach	Valley bottom width (ft)	Valley bottom length (mi)	Flood-plain width (ft)	Channel slope (ft/ft)	Sinuosity (ft/ft)	Active channel centerline length in 2005 (mi)	Active channel width in 2005 (ft)	Flood-plain width index (ft/ft)	Off-channel habitat index (mi/mi)	Brief description
Upper basin
1	1,748	12.3	484.5	0.0092	1.10	13.5	140.9	3.4	0.0	Steep, narrow, stable channel with plane-bed morphology; few in-stream gravel bars and side channels. Sediment supply is limited due to low rates of sediment yield from High Cascades tributaries and trapping by Carmen Smith Dam.
2	3,443	7.2	625.0	.0067	1.12	8.1	315.7	2.0	.2	Floodplain is incised within wide, glacially carved valley bottom; channel displays pool-riffle morphology and is predominantly stable except for dynamic areas near Dearborn Island and Delta Campground. Sediment supply is bolstered due to Horse Creek and other minor tributaries, but reach may still be supply limited, or close to equilibrium.
Middle basin
3	1,758	1.9	705.7	0.0057	2.29	4.3	114.8	6.1	.2	Steep, narrow channel downstream of Cougar Reservoir; reach is highly supply limited due to trapping by dam. Stable pool-riffle morphology, except for confluence with McKenzie, which was historically dynamic.
4	3,645	2.7	602.6	.0033	1.06	2.8	172.0	3.5	0.1	Short reach in between confluence of South Fork and Blue River; stable channel is relatively confined by narrow floodplain ,which is incised in wide, glacially carved valley bottom. Few gravel bars. Channel also confined by revetments alongside highway.
5	880	1.3	765.8	.0092	1.05	1.4	303.7	2.5	.0	Short, steep, highly confined channel downstream of Blue River Reservoir; few gravel bars or side-channels.
6	1,582	8.5	837.7	.0030	1.09	9.3	313.1	2.7	.2	Valley transitions from wide, glacially carved valley bottom to narrow canyon. Upstream of Finn Rock, wide unconstrained floodplain historically supported gravel bars and side channels; below Finn Rock, channel is confined with few bars or side channels.
7	1,367	8.0	508.2	.0033	1.11	8.9	246.7	2.1	0.1	Narrow confined reach with very stable planform; specific gage analysis shows stable channel geometry at Vida. Pool-riffle morphology with few gravel bars or side channels. Leaburg Dam at downstream end of reach.
8	2,421	4.9	689.6	.0023	1.14	5.6	293.3	2.4	.2	Narrow, confined reach with stable pool riffle morphology; overall planform controlled by bedrock outcrops. Several side-channels near Leaburg.
Lower basin
9	3,120	3.9	2,229.9	0.0016	1.11	4.3	436.7	5.1	0.6	Short reach in between Leaburg and Walterville Canals; transitional reach between confined, Middle basin and unconfined, alluvial lower reaches. Upper portion of reach is highly stable and confined, lower portion (near Deerhorn), has wide floodplain and numerous side-channels.
10	5,927	6.2	4,362.5	.0022	1.20	7.4	706.2	6.2	.7	Wide, unconfined floodplain; channel displays ‘wandering’ planform, with numerous multi-thread bends and gravel bars; many of the multi-channeled areas show dynamic change 1939–2005.
11	6,439	10.5	4,123.7	.0016	1.32	13.9	558.1	7.4	.7	Channel displays ‘wandering’ planform, flowing through wide, unconfined floodplain. Predominantly single-thread where channel flows against valley walls, particularly at constriction near Hayden Bridge and near Coburg. Multi-thread areas upstream of Hayden Bridge show greatest degree of historical dynamism.
12	3,302	3.3	4,259.1	.0016	1.06	3.4	508.9	8.4	.6	Wide, alluvial reach joins Willamette River; ‘wandering’ planform that historically displayed frequent channel change, particularly near the confluence area; specific gage anlaysis shows nearly 8 feet bed decline at Coburg between 1972 and 2008.