MONTANA DEPARTMENT HSH, WILDLIFE, AND PARKS 

 MRIS Reporting Program 



1.3.3 The EPA River Reach Numbering System 



The major stream reach identifier used in MRIS is an enhanced version of the EPA 

 River Reach File 1, adopted by the Bonneville Power Administration. There are 

 currentiy over 8,000 stream reaches in the MRIS master stream database. A reach is 

 defined as a stream segment located between two stream confluences. The structure 

 of the RRN is defined as: 



17010204 001 00.00 



/ / \ 



(hydrologic unit) (teach number) (mile poM) 



Montana is divided into 110 hydrologic units which define the major drainages in 

 the state (Appendix D-15). You wdll notice in the Fisheries and Stream Characteristics 

 Databases a field called Section. The reach boundaries for these stream segments did 

 not fit to a stream confluence and/or could not be moved without affecting the 

 biological integrity of the data. As a result, a stream in the Montana system is 

 identified by the 16 digit EPA RRN plus a 1 digit Section number used in these rare 

 cases where we could not determine an appropriate reach break. 



1.3.4 GIS and Querying the Montana Rivers Information System 



All data contained in the MRIS Reporting Program can also be visually displayed 

 and analyzed using ARC/INFO, a geographic information system (GIS). An 

 ARC/INFO work station is located in Kalispell and operated by MRIS staff. All data 

 are connected to an electronic 1:100 0(X) hydrography layer cross-referenced to the 

 EPA River Reach File 1 which is used as the MRIS master stream database. 



If you are interested in querying or analyzing MRIS data in a GIS format with any 

 of the available layers listed in Appendix D, contact: 



Fisheries, Janet Decker-Hess, 752-5501, ext. 228, 

 WUdlife, Gael Bissell, 752-5501, ext. 220, or 

 Recreation, Denise Davies, 752-5501, ext. 228. 



1-3 



