A Forest Management Nonpoint Source Risk Assessment 

 Geographic Information Systems Application 



By Don Potts' 



Introduction 



Risk Matrix Construction 



The assessment of nonpoint source pollu- 

 tion and cumulative watershed effects resulting 

 from forest management is proving to be a 

 difficult task. Application of Best Management 

 Practices (BMPs) does not provide an assess- 

 ment of condition, monitoring can be prohibi- 

 tively expensive, and our quantitative modeling 

 skills are in their infancy. An alternative ap- 

 proach, watershed risk analysis, may, however, 

 provide resource managers with a powerful tool 

 to assist in land-use decision making. In addi- 

 tion, Geographic Information Systems (GIS) 

 allow the correlation of land cover and topo- 

 graphic information such as terrain configura- 

 tion and drainage networks, thus making GIS 

 useful in assessing the potential effects of land- 

 use activities on water resources (Walsh 1985). 



We have developed a methodology to assist 

 forest managers in assessing nonpoint source 

 pollution and cumulative watershed effects by 

 combining watershed risk assessment with GIS . 

 The information required by the procedure is 

 available in the Rathead National Forest GIS. 

 Making a map with GIS is easy, but including 

 appropriate landscape attributes is difficult. The 

 key is the construction of a nonpoint source 

 pollution risk matrix. The results of such an 

 application are presented on a heavily impacted, 

 mixed-ownership watershed. 



Leopold and others (1971) were among the 

 first to propose the use of an environmental 

 matrix to evaluate potential environmental im- 

 pact. The matrix provides a comparatively 

 simple system intended to be a guide in the 

 impact assessment process. This approach was 

 adopted by Rickert and others (1978) to evalu- 

 ate erosion potential for the Oregon 208 non- 

 point source assessment project and by Brown 

 in and others (1979) as a guide for land-use 

 planning. 



The "risk" matrices developed in these stud- 

 ies assessed the relative impacts of various 

 land-use activities on different combinations of 

 slope and substrate erodibility. Forest manage- 

 ment practices were among the land-use activi- 

 ties considered, but Brown in and others sug- 

 gested that matrices should be developed re- 

 gionally to reflect local conditions, practices, 

 and socioeconomic considerations. 



Therefore, we contacted a large group of 

 soil and water specialists and silviculturists, 

 representing land management agencies and 

 the forest products industry in Montana, to 

 build the Montana erosion-impact matrix. We 

 quickly learned that it was not going to be as 

 easy as we thought. There was considerable 



'Dr. Don Potts is a Professor with the Univer- 

 sity of Montana's School of Forestry in Missoula, 

 Montana. 



Flathead Basin Cooperative Program Final Report 



Page 115 



