What is an appropriate range of CN value for wetlands? Keep in mind that not all wetlands are depressions with standing water. Some wetlands are so defined when the surface is just moist, or the hydric soil is present, or special vegetation that thrives on wet soil has taken root.
Each watershed uses a Curve Number (CN) to characterize the runoff properties for a particular soil and ground cover. The CN value is a primary input parameter for the SCS runoff equation. High CN values (such as 98 for pavement) cause most of the rainfall to appear as runoff, with minimal losses. Lower values (such as 58 for certain wooded areas), correspond to an increased ability of the soil to retain rainfall, and will produce much less runoff.
Attached technical report gives some more information about determining CN avlues and values used in practice.
Wetlands are a hydrologic typology which is rarely mentiond in studies. Because of the dynamics of wetlands the variation of CN for runoff could be big. Like 10 (hydric soil, dry/ moist) to 100 (surface water system).
In your specific case the CN value for wetlands depends on the hydrological (both surface and subsurface) situation as well as soil characteristics and vegetation types.
Curve number for water bodies and wet land having water for different hydrologic soil groups are 0 (zero). But some wetlands have just moist with vegetation, under such situation area can be put under Grass lands/ pasture land / range land with good condition then CN for hydrologic soil group A having CN 39, for soil group B CN is 61, for soil group C CN is 74 and soil group D CN is 80 as per literature available.
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