MDT Montana Wetland Assessment Method May 25. 1999 



First, estimate the area of jurisdictional wetland that is subject to periodic flooding within the AA. This can be based on aerial photos, 

 water marks, silt lines, alternating layers of leaves and fine sediment, ice scars, drift hnes, sediment deposition, directionally bent 

 vegetation, or other physical evidence. Do not include non-wetland open water channel in this estimate. Next, determine the 

 approximate percentage of jurisdictional wetland subject to flooding that is classified in forested or scrub-shrub classes (note: in some 

 cases it may be appropnate to consider dense, extensive stands of hardy persistent emergent vegetation, such as cattail, as scrub- 

 shrub for purposes of this form, as these stands act as primary floodwater attenuators in some parts of the state. If this situation 

 applies, note in the comments section). Finally, determine whether or not the wetland contains a restricted outlet and circle the 

 appropriate fiinctional points and rating. 



ii. Indicate whether there are residences, businesses, or other features (parks, sports fields, historic sites, roads, etc.) that could be 

 damaged by floodwaters located within 0.5 mile downstream of the AA. Describe these features in the comments section. 



14F. Short and Long Term Surface Water Storage: This field assesses the potential of the AA to capture and hold surface water 

 originating from floodmg, precipitation, upland surface (sheetflow) or subsurface (groundwater) flow. If jurisdictional wetlands in the 

 AA are not subject to flooding or ponding, circle NA where indicated on the data form and proceed with the evaluation. 



Variables used to assess this fiinction are: estimated ma.ximum acre feet of water contained in wetlands that are subject to flooding or 

 ponding; duration of surface water, and flood frequency. Wetlands able to contaio more water volume (acre feet) are more effective at 

 storing water than wetlands restricted to less capacity under the same conditions. Wetlands that contain surface water for longer periods 

 are capable of storage for slower release into the local system than are wetlands that store surface waters for shorter penods. assisting 

 in the stabilization of local flow regimes. Wetlands that flood or pond frequently provide water storage functions more often than do 

 wetlands that flood or pond less fi^quenth'. 



i. Rating. Working from top to bottom, use the matrix on the data form to arrive at [circle] the functional points and rating [H = high, 

 M = moderate, or L = low] for this function. First, estimate the maximum acre feet of water contained vnlhm jurisdictional wetland 

 subject to periodic flooding or ponding within the AA. This can be based on observation, aerial photos, water marks, and other 

 physical evidence (indicate basis in comments). Next determine the maximum duration of surface water and flooded or ponded 

 wetlands using the definitions provided above under 14C. Finally, estimate (based on photographs. NRCS data, interviews, knowledge 

 of the area, etc.) whether the jurisdictional wetlands that flood or pond do so at a fi^uency greater than or less than 5 out of every 10 

 years and circle the appropriate functional points and rating. 



14G. Sediment/Nutrient/Toiicant Retention and Removal: This field assesses the ability of the AA to retain sediments and retain 

 and remove excess nutrients and toxicants. This field only appUes to wetlands with potential to recerve sediments and excess nutrients 

 or toxicants through influx of surface or ground water or direct input. If no wetlands in the AA are subject to such input circle NA 

 where indicated on the data form and proceed with the evaluation. Nitrogen and phosphorus are the two nutrients most often 

 associated with water pollution; both occur in high concentrations in fertilizers and discharges from sewage treatment plants and 

 livestock operations, and excessrve amounts of either can result in algal blooms and subsequent oxygen deficiencies in receiving 

 waters. Toxicants include pesticides, herbicides, petroleimi products, metals, and other potentially harmful constituents. 



The assessment is based on the site's proximity to sediment/nutrient/toxicant sources; percent cover of vegetation; evidence of floodmg 

 or ponding; and presence or absence of an outlet. Wetlands with the potential to receive and successfully process sediment nutnents. 

 and toxicants provide these fiinctions at a higher capacity than do wetlands that receive excessive amoimts of these constituents such 

 that other functions are impaired. Generalh", a wetland 's ability to uptake nutrients and toxicants and filter sediment increases with the 

 density of its vegetation. Flooded or ponded wetlands are indicative of sites that retain water; these areas allow sediments to settle out 

 and increase nutrient/toxicant contact time with vegetation, facihtating uptake. Sites with no outlets or restricted outlets retain w ater 

 longer (allow more settling and vegetation contact) than do sites with unrestricted outlets. 



L Rating. Working from top to bottom, use the matrix on the data form to arrive at [circle] the functional points and rating [H = high, 

 M = moderate, or L = low] for this function. 



First, determine if the AA receives or surrounding lands have the potential to deliver low to moderate levels of sediments, nutrients, or 

 toxicants such that other functions in the AA are not substantialh' impaired (e.g.. the wetland is processing these inputs but is not 

 significantly affected by them). Observation of some sedimentation, relativeh' minor potential sources of nutrients or toxicants, or 

 signs of minor to moderate eutrophication would be indicative of this input level. 



If the waterbody within the AA is listed on the MDEQ list of Waterbodies in Need of Total Maximum Daily Load (TMDL) 



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