USGS Open-File Report 2012-1038 - Tidal Wetlands of the Yaquina and Alsea River Estuaries, Oregon: Geographic Information Systems Layer Development and Recommendations for National Wetlands Inventory Revisions

Results

Recommended Revisions to Cowardin et al. (1979) Classification

The enhanced NWI shapefiles contain recommended revisions to the Cowardin et al. classification (system, subsystem, class, and/or modifiers) for 286 NWI polygons in the Yaquina estuary (1,133 acres) and 83 NWI polygons in the Alsea basin (322 acres) (figs. 4 and 5). Many of the changes consisted of adding the "diked" modifier to diked former tidal wetlands that are currently palustrine wetlands. For example, PEMC was changed to PEMCh for 514 acres in the Yaquina estuary, and PEMA was changed to PEMAh for 32 acres in the Alsea estuary (tables 5 and 6). Other common changes were the addition of a tidally influenced hydrologic modifier to palustrine wetlands, and a change from the palustrine to the estuarine class based on field measurements of salinity data. Substantial acreages of likely former tidal wetland were identified that are currently classified as upland in the NWI (tables 5 and 6; see section, "Likely Former Tidal Wetlands Classified as Upland in the NWI").

Figure 4. Map of recommended National Wetland Inventory Cowardin et al. (1979) classification revisions resulting from this project for the Yaquina estuary, Oregon, including areas identified as likely former tidal wetlands ("FTW"). NWI polygons without recommended revisions are shown as outlines only (fill = background color). Source data: Table 7—Yaquina_tidal_NWI_2011. Projection: UTM Zone 10N NAD83.

Figure 5. Map of recommended National Wetlands Inventory Cowardin et al. (1979) classification revisions resulting from this project for the Alsea estuary, Oregon, including areas identified as likely former tidal wetlands ("FTW"). NWI polygons without recommended revisions are shown as outlines only (fill=background color). Source data: Table 7—Alsea_tidal_NWI_2011. Projection: UTM Zone 10N NAD83.

Table 5. Total area (acres) of recommended changes to NWI Cowardin et al. classification, by original NWI classification, Yaquina estuary, Oregon.

[Table includes only those original or revised classifications that totaled more than 1 acre]


	Recommended revised Cowardin et al. classification (or other designation^*): area in acres
	E2EM/SSP	E2EMP	E2FOP	E2SSP	FTW¹	PABFh	PEM/SSCh	PEM/SSR	PEMAdh	PEMAh	PEMCh	PEMFh	PFOAh	PFOR	PSS/EMAh	PSS/EMCh	PSSAh	PSSCh	PSSR	Total
PABF						5.8														5.8
PEM/SSA								15.9												15.9
PEM/SSC	18.1						14.3													32.4
PEMA		4.0							38.9	170.1	10.1									227.4
PEMAh		19.5																		19.5
PEMC		3.3									514.3									518.0
PEMCd		46.3																		46.3
PEMF												21.3								21.3
PEMR		49.3									1.1									51.2
PFOA			1.8										6.4	16.1						24.6
PFOC			2.4											0.4						5.7
PSS/EMA															8.8					8.8
PSS/EMC																36.6				36.6
PSSA				9.0													10.9		6.1	27.8
PSSC																		60.3		60.3
PSSR				3.8														2.9		6.7
U		1.8			441.0															442.8
Total	18.1	128.2	5.5	13.5	441.0	5.8	14.3	15.9	38.9	170.1	525.5	21.3	6.4	16.8	8.8	36.6	10.9	63.2	6.1	1574.4

¹FTW is not a Cowardin et al. classification, but a designation indicating a likely Former Tidal Wetland, currently disconnected from tidal flow but with land surfaces at elevations within tidal range.

Table 6. Total area (acres) of recommended changes to NWI Cowardin et al. classification, by original NWI classification, Alsea estuary, Oregon.

[Table includes only those original or revised classifications that totaled more than 1 acre]


	Recommended revised Cowardin et al. classification (or other designation^*): area in acres
	E2EMN	E2EMP	E2FOP	E2SSP	E2USN	FTW¹	PEMAdh	PEMAh	PEMCh	PEMR	PFOAh	PFOR	PSS/FOAh	PSS/FOCh	PSSAh	PSSR	Total
PEMA		21.8						31.8		13.2							66.8
PEMAd							75.3										75.3
PEMC		2.7							9.9	4.5							17.1
PEMCh										7.3							7.3
PEMR		51.3															51.3
PEMS		8.3															8.3
PFOA			1.5								10.5						12.0
PFOB			1.7														1.7
PFOCh												2.4					2.4
PFOR			4.4														4.4
PSS/FOA													24.3				24.3
PSS/FOC														3.2			3.2
PSSA												1.5			1.8	1.9	5.2
PSSR				6.6													6.6
R1UBV					2.2												2.2
R1UBVh					5.9												5.9
U	12.5		4.5	0.6		51.0						6.3					74.9
Total	12.5	84.1	12.9	7.2	8.0	51.0	75.3	31.8	9.9	24.9	10.5	11.0	24.3	3.2	1.8	1.9	373.0

Likely Former Tidal Wetlands Classified as Upland in the NWI

Analysis of LiDAR data revealed many likely former tidal wetlands that were classified as upland in the National Wetlands Inventory (64 NWI polygons totaling 441 acres in the Yaquina estuary, and 16 NWI polygons totaling 51 acres in the Alsea estuary) (figs. 4 and 5; tables 5 and 6). Cowardin et al. classification of these former tidal wetlands was beyond the scope of this project because field evaluation would have been needed to determine the hydrologic status of these areas.

GIS Data for 1999 Prioritization Sites

GIS datasets were created for the 1999 prioritization sites as well as for several new prioritization sites in each estuary (figs. 6 and 7). The GIS datasets contain 49 prioritization sites totaling 2,177 acres in the Yaquina estuary, and 39 prioritization sites totaling 1,045 acres in the Alsea estuary. The prioritization sites consisted of 494 and 192 underlying NWI polygons in the Yaquina and Alsea estuaries, respectively.

Figure 6. Map of tidal wetlands and likely former tidal wetlands of the Yaquina River estuary, Oregon: prioritization sites from the 1999 tidal wetland prioritization (Brophy 1999), plus new sites identified in the current study (sites Y44 through Y49). Prioritization sites, created by merging NWI polygons, provide analysis units suitable for action planning for tidal wetland restoration and conservation. Colored areas are prioritization sites; each site is colored separately, and labels indicate site numbers. Background is NWI mapping (gray lines). Source data: Table 7—Yaquina_tidal_wetlands_2011. Projection: UTM Zone 10N NAD83.

Figure 7. Map of tidal wetlands and likely former tidal wetlands of the Alsea River estuary, Oregon: Prioritization sites from the 1999 tidal wetland prioritization (Brophy 1999), plus new sites identified in the current study (sites A38 through A41). Prioritization sites, created by merging NWI polygons, provide analysis units suitable for action planning for tidal wetland restoration and conservation. Colored areas are prioritization sites; each site is colored separately, and labels indicate site numbers. Background is NWI mapping (gray lines). Source data: Table 7—Alsea_tidal_wetlands_2011. Projection: UTM Zone 10N NAD83.

New Prioritization Sites

Previously described LiDAR-derived elevations and NWI classification analysis allowed us to identify tidal wetlands (or former tidal wetlands) that had not been described in the 1999 study. In most cases, these tidal wetlands were already classified as wetlands in the NWI, but they were not previously classified as tidal wetlands nor did they have special modifiers suggesting hydrologic alterations that would restrict tidal flows. In two cases, new sites were identified that were classified as upland in the NWI, but which were at elevations within tidal range. These two cases were prioritization sites A38 and A40, on land owned by U.S. Forest Service (USFS) and U.S. Bureau of Land Management (BLM), near the Drift Creek tidal wetland restoration project (prioritization site A26) (fig. 7). LiDAR data were used to digitize new prioritization site boundaries using the methods described in section, "Likely Former Tidal Wetlands Classified as Upland in the NWI".

The new prioritization sites in each estuary are listed, with approximate acreages. Field visits by a knowledgeable wetland scientist are recommended to determine the state and federal regulatory status of these areas.

Yaquina estuary: New prioritization sites (fig. 6)
- Site Y44 (7 acres): Partially filled forested tidal wetland at the mouth of Olalla Slough.
- Site Y45 (13 acres): Diked pasture in the upper estuary, probably former tidal swamp.
- Site Y46 (4 acres): Diked pasture in the upper estuary, probably former tidal swamp.
- Site Y47 (12 acres): Undiked tidal swamp (forested and scrub-shrub tidal wetland) in the upper estuary.
- Site Y49 (3 acres): Undiked tidal marsh just outside the tide gates on Depot Slough.Site Y48 (2 acres): Fringing marsh on south bank of the Yaquina River, just upstream of site Y3.

Alsea estuary: New prioritization sites (fig. 7)
- Site A38 (8 acres): Tidal marsh and tidal swamp (forested tidal wetland) on the northern bank of Drift Creek at river mile 2. This is a USFS restoration site.
- Site A39 (6 acres): Freshwater tidal marsh (probably former tidal swamp) at river mile 3 on Drift Creek.
- Site A40 (9 acres): Forested tidal wetland or former tidal wetland, immediately east of the large USFS tidal marsh restoration area on Drift Creek. A site visit or information from USFS is needed to determine the current hydrologic status.
- Site A41 (2 acres): Small possible tidal swamp opposite mouth of Risley Creek and Bain Slough.

Revisions to Prioritization Site Attributes

New information on prioritization site characteristics (changes since 1999, or information not provided in 1999) was generated for 15 of 49 prioritization sites in the Yaquina estuary and 8 of 39 prioritization sites in the Alsea estuary. The new information can be found in the attribute tables of the prioritization site shapefiles (see section, "Downloadable Wetland Shapefiles"). Most of the new information relates to restoration activities or field observations since 1999.