GEOLOGICAL SURVEY OF CANADA OPEN FILE REPORT 2522 A DEBRIS FLOW BASIN AND EVENT DATA BASE FORMAT WITH AN EXAMPLE DATA SET FROM SOUTHWESTERN BRITISH COLUMBIA By Oldrich Hungr Thurber Engineering Suite 200-1445 West Georgia Vancouver, B.C. V6G 2T3 and Lionel E. Jackson, Jr. Geological Survey of Canada Terrain Sciences Division 100 West Pender Street Vancouver, B.C. V6B 1R8 March 1992 ABSTRACT Debris flow is a widespread phenomenon in the Canadian Cordillera where it has caused death, property damage and disruption of commerce. This publication presents a systematic inventory of past debris flow events in an area of southwestern British Columbia and an iteration of factors that may have been important variables in the generation of these events. This information is presented in the form of a computer data base using dBASE IV. Statistical analysis of these variables may prove useful in screening undocumented basins for debris flow hazard within this region and in mountainous regions elsewhere. INTRODUCTION Debris flows are among the most widespread and destructive forms of rapid mass wasting in mountainous areas of the world. They have caused death, property damage and disruption of commerce in the Canadian Cordillera (Lister et al. 1984; Van Dine 1985). Debris flow is a naturally occurring process in mountain drainage basins. Mitigation of debris flow hazard is most economically achieved by avoiding hazardous areas. This requires a systematic inventory of past debris flow events and examination of mountain drainage basins with an eye to the presence of factors that make debris flow likely. Examples of the application of drainage basin morphometry, inventory of sediment source areas and compilation of past debris flow activity to evaluation of the presence, magnitude and frequency of debris flow hazard can be found in Hungr et al. (1984) Jackson (1987) and Jackson et al. (1987). This report presents a data base format using the widely used dBASE IV data base (version 1.1) software package (distributed by Borland) for assembling data on the physical characteristics of drainage basins susceptible to debris flow generation and data on individual debris flow events. The variables included in this format are factors the authors have found to be important in preparing inventories of known debris flow-prone basins; assessing the potential for basins to produce debris flows; estimating the size and frequency of future debris flows; and predicting the runout distance of debris flows. Statistical analysis of these variables may prove useful in screening undocumented basins in southwestern British Columbia and in other mountainous regions of Canada and elsewhere for debris flow hazard. A data set from drainage basins in southwestern British Columbia is included. This format and data compilation was produced under contract 23254-9-0566/01-XSB by Thurber Engineering. It is contained in a catalogue called DF.CAT consisting of the following files: 1. Database (.DBF) files BASINS.DBF Data on physical characteristics of debris flow-susceptible drainage basins. EVENTS.DBF Data on historical debris flow events in an area of southwestern British Columbia. 2. Form (.SCN, .FMT) files BASIN_1 to BASIN_9, EVENT_1 to EVENT_5: Files containing the custom screen formats used to review and input the data. 3. Application files BASIN_ED and EVENT_ED: Programs that invoke the above form files in the correct sequence. 4. Query files and report files (created as needed by the user). An explanation of each field and abbreviations used for variables are presented below. Not all variables in the data base files need to be provided. The user can create short forms to access a particular selection of variables from the data bases using the form building facilities of dBASE IV. Use the "Forms " selection in the control centre. **************************************************************** File BASINS.DBF R. REFERENCE PARAMETERS R1_PREFIX Region prefix: (SQ-Howe Sound; F3 SE quadrant of Fraser Lowland) R1_ID_NUM Basin I.D. number (assign consecutively) R2_NAME Stream name (if available). R3_NORTH Fan apex UMT coordinates -northing R4_EAST -easting DRAINAGE GEOMETRY D1_AREA Drainage area (km2) D2_MAIN Length of main branch, fan apex to highest point in basin (m) D3_BRANCH Combined length of other branches D4_ELEV Main channel elevation difference, fan apex to highest point in basin (m) D5_SLOPE Average slope of main branch (degrees) D6_STEEP Slope of steepest segment of main channel (must be > 100m in terms of elevation difference) D7_LG_ST Length of steepest major segment (m) D8_PR_TYPE Type of profile U-uniform S-stepped C-concave V-convex D9_AZIM Mean azimuth of main branch (degrees) D10_D_TYP Drainage type A-open slope, (straight contours) B-wide bowl (semi-circular contours) C-narrow bowl D-Gully (V-shaped contours) E-cirque and scarp F-hanging valley and scarp O-other (describe) D11_SYMM Degree of symmetry (estimated % of drainage area located to larger side of the main branch F. FAN GEOMETRY F1_AREA Area (m2, subaerial extent only) F2_HEIGHT Toe to apex height (m, subaerial extent only) F3_SLOPE Slope of steepest major segment (>50 m long, degrees) F4_ST_SL Slope of the steepest major segment (>50 m long, degrees, subaerial extent, only) F5_PROFILE Type of profile: U-uniform C-concave V-convex F6_TYPE Type of fan A-circular B-partly constricted C-constricted D-segmented E-partly coalesced (sharing < 25% of perimeter with fan(s) of another stream(s) F-coalesced (>25% shared) G-colluvial apron (nearly 100% shared) F7_SUBAQ Area of subaqueous portion (m2 fans along lakes and ocean) F8_TRUNC Truncated fan (Y/N) B. BEDROCK GEOLOGY B1_D_TYPE Dominant lithology B2_D_PERC % basin represented B3_S_TYPE Secondary type B4_S_PERC % area Type categories: IP-plutonic V-volcanic MQ-metamorphic, quartzose MM-metamorphic, micaceous SS-sandstones and conglomerates SP-mudstones and claystone B5_FAULTS Known faults in the basin? (Y/N) B6_SAGS Sagging, gravitational slope disturbances? (Y/N) B7_COMM Comments re bedrock geology S. SURFICIAL GEOLOGY S1_D_TYPE Dominant type S1_D_PERC % area represented S3_S_TYPE Secondary type S4_S_Perc % area Type categories: B-clean bedrock VC-coarse colluvial veneer (talus) VF-fine colluvial veneer CC-coarse deep colluvium (talus) CF-fine deep colluvium (landslide debris) GS-glacial till VO-organic veneer ?-other S5_COMM Comments re surficial geology V. VEGETATION COVER V1_D_TYPE Dominant type V2_D_PERC % area V3_S_TYPE Secondary type V4_S_PERC % area Type categories: R-rock outcroppings A-alpine tundra or avalanche paths PC-primary forest (conifers) MC-mature second growth (conifers) YC-young second growth (20-50 years age) D-deciduous or mixed forest RP-recent planation (10-20 years) RN-recent natural regrowth (10-20 years) CL-recent clearcut (0-10 years) B-recent burn (0-10 years) X-disturbed slopes (landsliding, erosion, cuts and fills) V5_ROADS Road construction- total length of roads (m) V6_SLASH Presence of slash debris (0-do not know, 1-major, 2- moderate, 3- minor) V7_BUFFERS Stream buffers used in logging operations (Y/N) V8_COMM comments re vegetation O. OTHER PROCESSES (indicate on scale of 0-3: 0- do not know, 1- major, 2- moderate, 3-minor) O1_AVALAN Snow avalanching O2_WIND Recent wind fall O3_SLIDE Debris sliding O4_FILL Road fill and cut failures O5_RSLIDE Rockslide O6_RFALL Rockfall O7_GULLY Gully erosion O8_SNOWF Permanent snowfields O9_GLAC Glaciers O_COMM Other processes (specify) C. DEBRIS SOURCES IN CHANNEL C1_P_TYP Primary: channel type C2_P_WIDTH width (m) C3_P_BANK bank height (m) C4_P_HT ave. bank height (m) C5_S_SLOPE ave. bed slope (degrees) C6_S_LENG ave. reach length (m) C7_S_TYP Secondary: channel type C8_S_WIDTH channel width (m) C9_S_BANK bank type C10_S_HT ave. bank height (m) C11_S_SLOPE ave. bed slope (degrees) C12_S_LENG ave. reach length Channel type categories: 1-bedrock channel 2-bedrock with a veneer of boulders and cobbles 3-large boulders 4-small boulders 5-cobbles and pebbles Bank categories: 1-stable rocks and cliffs 2-low banks 3-stable vegetated banks 4-stable banks alternating with small talus or debris cones 5-moderately unstable:weak rock, steep slopes, occasional debris slides, inactive talus 6-unstable: widespread debris sliding, unstable fills, active talus, very steep ravelling slopes I. RECORD OF DEBRIS FLOW AND OTHER INSTABILITY I1_EVENTS List of event I.D. numbers I2-I6 Evidence suggesting prehistoric or poorly documented debris activity (Y if present, N if positively not present, blank if not known) I2_BOULDER Large boulders on fan I3_BERMS Bouldery berms or lobes on fan I4_LEVEES Debris flow levees on fan I5_TREE_DA Debris flow damaged trees I6_OTHER Other similar evidence N1_NOTES Other comments *************************************************************** File EVENTS.DBF ER. REFERENCE AND CLASSIFICATION RNUM Event I.D. number ER_2_DATE Date of event ER_3_BASIN Drainage I.D. number ER_4_NORTH UTM coordinates, fan apex, -northing ER_5_EAST -easting ER_6_TIME Time period of main activity (from..to) ER_7_SOURC Sources of information concerning the event (companies, individuals, reports, print and broadcast media articles and reports) EC. EVENT CLASSIFICATION EC_1_TYPE Type of event: DT- debris flow- identified by the following evidence: Surge discharges considerably in excess of expected maximum flood discharge Movement of liquefied debris masses without water traction Excessive movement velocities Large boulders moved Relatively thick deposits (> 1m) DF- debris flood- large quantities of debris may be transported but without the above the above aspects. Deposits form thin sheets of relatively fine debris (pebbles and cobbles). DS- debris slide- shallow instability on a steep slope, with total displacement < one-half the length of the detatchment scar DA- debris avalanche- shallow instability with large displacement, not reaching an established channel to become a debris flow EC_2_MAG Magnitude (estimated total volume of material involved (m3) EI. INITIATION TRIGGERS (DEBRIS FLOWS ONLY) EI_1_INIT Number of initiation points EI_2_TRIG Main initiation trigger type DS-debris slide RS-rockslide CH-channel-bed instability F -fill failure (from a road) C -cut failure (from a road) AV-snow avalanche(s) O -other ES. MAIN STARTING ZONE OR TRIGGER ES_1_HIGH Highest point elevation (m) ES_2_LOW Lowest point elevation (m) ES_3_WIDTH Mean width (m) ES_4_SLOPE Ave. slope angle (degrees) ES_5_VOLUM Estimated volume of detachment (m3) ES_6_MATL Predominant material involved: S-soil B-boulders, talus R-rock ES_7_ROCK Bedrock in base of scar? (Y/N) ES_8_CLEAR Fresh clearcut or burn (0-10 years (Y/N) ET. TRANSPORTATION ZONE ET_1_LONG Length of longest branch (m) ET_2_OTHER Combined lengths of all branches (m) ET_3_WIDTH Maximum flow cross-section width (m) ET_4_DEPTH mean depth (m) ET_5_DISC Maximum flow discharge at a point (m3/s) ET_5A_VEL Velocity at a point ET_6_HOW Velocity determination method: S-from superelevation formula D-direct measurement O-other means ED. DEPOSIT INFORMATION ED_1_HIGH Highest elevation of main deposit ED_1A_ANG Bed slope at highest elevation ED_2_LOW Lowest elevation of the main deposit (m) ED_2A_ANG Bed slope at lowest deposit elevation (m) ED_3_LENGT Maximum plan length of main deposit (m) ED_4_WID Maximum plan width of main deposit (m) ED_5_AREA Area of main deposit (m2) ED_6_VOL Estimated volume of main deposit (m3) ED_7_AR2 Area covered by secondary deposits downstream of main deposition area (m2) ED_8_GRAIN Modal grain size of main deposit (mm) ED_9_MAX Maximum grain size of main deposit (mm) ED_10_ORG Estimated organic content (logs, stumps, branches etc. in % of volume) EA. DAMAGE EA_1_PERS Persons killed or missing EA_2_INJ Persons injured EA_3_DAM Area of land affected by damages (m2) EA_4_HOU Buildings destroyed EA_5_HD Buildings damaged EA_6_BRI Bridges destroyed EA_7_BD Bridges damaged EA_8_VAL Estimated value of damages (current $) EA_9_CLEAN Cost of cleanup and rescue (current $) EA_10_REP Cost of repairs and reconstruction (current $) EN_1_NOTE Notes concerning this event ***************************************************************** All of the above listed basin parameters with the exception of categories C. DEBRIS SOURCES IN CHANNEL and I. RECORD OF DEBRIS FLOW AND OTHER INSTABILITY can be measured or described using aerial photography and topographic maps. Category C. requires a detailed channel survey. This data is necessary for prediction of debris flow volumes (Hungr et al. 1984). Category I. requires a detailed survey of the fan surface and exposures of fan stratigraphy (see Jackson 1987). Debris flow event documentation requires data from on site inspection and a variety of other sources. REFERENCES Hungr, O., Morgan, G.C. and Kellerhalls, R. 1984: Quantitative analysis of debris torrent hazards for design of remedial measures; Canadian Geotechnical Journal, v. 21, p. 663-677. Jackson, L.E. Jr. 1987: Debris flow hazard in the Canadian Rocky Mountains; Geological Survey of Canada Paper 86-11, 20 p. Jackson, L.E. Jr., Kostaschuk, R.A., MacDonald, G.M. 1987: Identification of debris flow hazard on alluvial fans in the Canadian Rocky Mountains; in Costa, J.E. and Wieczorek, G.F. (eds.) Debris flows/avalanches: process, recognition, and mitigation; Geological Society of America, Reviews in Engineering Geology Volume III, p. 115-124. Lister, D.R., Morgan, G.C., VanDine, D.F., Kerr, J.W.G. 1984: Debris torrents in Howe Sound, British Columbia; Proceedings 4th International Symposium on Landslides, Toronto, v. 1, p. 649-654. Van Dine, D.F. 1985: Debris flows and debris torrents in the southern Canadian Cordillera; Canadian Geotechnical Journal, v. 22, p. 44-68.