LLWW Classification

LLWW CLASSIFICATION: Enhanced Classification for Landscape Position, Landform, Water Flow Path, and Waterbody Type

How to enhance NWI Classifications

To enhance the utility of NWI data for better characterizing wetlands and for preparing preliminary assessments of wetland functions from the NWI database, additional features had to be added to the NWI data. Key features included hydrogeomorphic features, specifically landscape position, landform, and water flow path. In addition, it was deemed important to better characterize waterbodies to identify a wide variety of pond types, and to separate natural lakes from created lakes, among other things, so waterbody type was also added to the NWI classification. Collectively, these descriptors have been referred to as "LLWW descriptors" with the letters representing the first letter of each additional descriptor (landscape position, landform, water flow path, and waterbody type). A set of dichotomous keys have been developed to define and classify these features. Figure 1 illustrates how these descriptors are applied to a nontidal region.

Five landscape positions for wetlands are recognized: marine (ocean intertidal shores), estuarine (estuarine intertidal shores), lentic (lake or reservoir shores), lotic (river and stream shores and floodplains), and terrene (isolated or not subject to overflow from rivers, streams, or lakes). Landforms include basin (depression), flat (broad nearly level landform), floodplain (subject to river overflow), fringe (shallow-water wetland, bank, or tidal wetland with unrestricted flow), and slope (>2% slope). Several water flow paths are defined: inflow, outflow, throughflow, bidirectional-tidal, bidirectional-nontidal, and isolated (geographically isolated; often surrounded by nonhydric soils). A set of simplified keys have also been applied for these descriptors (see Table 1 below).

Download the LLWW Tools Add-in for ArcGIS 10

A tool has been developed to help classify wetlands in areas not containing NWI+ data. It involves both automated and manual routines.  For the tool, contact Kevin McGuckin at: 

Print a Copy of the Dichotomous Keys

The full set of dichotomous keys are published in "Dichotomous Keys and Mapping Codes for Wetland Landscape Position, Landform, Water Flow Path, and Waterbody Type: Version n3.0". (December 2014)

Dichotomous Keys and Mapping Codes for Wetland Landscape Position, Landform, Water Flow Path, and Waterbody Type Descriptors: Version 2.0. (August 2011)

Dichotomous Keys and Mapping Codes for Wetland Landscape Positon, Landform, Water Flow Path, and Waterbody Type Descriptors. (September 2003)

 

Table 1. Simplified Keys for Wetland Landscape Position, Landform, and Water Flow Path
Landscape Position
1. Wetland borders a waterbody (river, stream, lake, reservoir, estuary, or ocean) 2
1. Wetland does not border a waterbody; it is completely surrounded by upland Terrene
2. Wetland lies along an ocean shore and is subject to tidal flooding Marine
2. Wetland does not lie along an ocean shore 3
3. Wetland lies along an estuary (salt to brackish tidal waters) and is subject to tidal flooding Estuarine
3. Wetland does not lie along an estuary or if so, it is not subject to tidal flooding 4
4. Wetland lies along a lake or reservoir or within its basin Lentic
4. Wetland lies along a river or stream, or if along an estuary or estuarine wetland it is not subject to tidal flooding (except storm tides) 5
5. Wetland is the source of a river or stream and although the watercourse originates from the wetland, it does not flow through the entire length of the wetland, or it borders an estuarine wetland (subject to storm tides only) Terrene
5. River or stream flows through the wetland 6
6. Wetland is periodically flooded by river or stream overflow Lotic1
6. Wetland is not periodically flooded by the river or stream Terrene
Landform
1. Wetland occurs on a slope >2% Slope
1. Wetland does not occur on a slope >2% 2
2. Wetland forms an island completely surrounded by water (excluding wetlands where extensive grid ditching might create this condition at a small scale) Island
2. Wetland does not form on an island 3
3. Wetland occurs in the shallow water zone of a permanent nontidal waterbody, the intertidal zone of an estuary, or the regularly flooded (daily tidal inundation) zone of freshwater tidal wetlands Fringe
3. Wetland does not occur in these waters or intertidal zones 4
4. Wetland forms a nonvegetated bank or is within the banks of a river or stream Fringe
4. Wetland is not a nonvegetated river or stream bank or within the banks 5
5. Wetland occurs on an active alluvial plain Floodplain*
5. Wetland does not occur on an active floodplain 6
6. Wetland occurs in a distinct depression Basin
6. Wetland occurs on a nearly level landform Flat
Water Flow Path2
1. Wetland is typically surrounded by upland (nonhydric soil); receives precipitation and runoff from adjacent areas with no apparent outflow Isolated**
1. Wetland is not isolated 2
2. Wetland is a sink receiving water from a river, stream, or other surface water source, lacking surface water outflow Inflow
2. Wetland is not a sink; surface water flows through or out of the wetland 3
3. Wetland is subjected to tidal flooding Bidirectional-Tidal
3. Wetland is not tidally influenced 4
4. Water flows out of the wetland, but does not flow into this wetland from another source Outflow***
4. Water flows in and out of the wetland 5
5. Water flows through the wetland, often coming from upstream or uphill sources Throughflow***
5. Wetland is along a lake or reservoir and its water levels are subjected to the rise and fall of this waterbody; no stream flow through the wetland Bidirectional-Nontidal
Notes
1 Lotic wetlands are separated into river and stream sections (based on watercourse width - polygon = Lotic River vs. linear = Lotic Stream at a scale of 1:24,000) and can then be divided into one of five gradients: 1) high (e.g., steep slopes), 2) middle (e.g., moderate slopes), 3) low (e.g., considerable floodplain development and slow-moving streams), 4) intermittent, and 5) tidal.  
2 Surface water connections are emphasized because they are more readily identified than groundwater linkages. Note: Major water flow paths are indicated; more detailed relationships can be described using the keys.  The “Paludified” water flow path is not included in this simple key; paludified wetlands are common in northern climates where bogs are one of the most common wetland types in the region.  
* Basin and Flat sub-landforms can be identified within this landform when desirable.  
** Wetland is geographically isolated; hydrological relationship to other wetlands and watercourses may be more complex than can be determined by simple visual assessment of surface water conditions.  
*** If stream data are separated into intermittent and perennial reaches, consider separating Outflow and Throughflow into perennial (OU and TH) and intermittent (OI and TI) water flow paths.