Beach Dynamics of Sebago Lake A Report on the Results of Beach Profiling by Robert A. Johnston and Martha N. Mixon Maine Geological Survey Natural Resources Information and Mapping Center DEPARTMENT OF CONSERVATION Robert G. Marvinney, State Geologist Open-File 98-122 Beach Dy namics of Se bago Lake A Report on the Re sults of Beach Pro fil ing Rob ert A. Johnston Maine Geo logi cal Sur vey 22 State House Stati on Augusta, Maine 04333 Martha N. Mixon F. M. Beck, Inc. One Main Street Yarmouth, Maine 04096 Maine Geo logi cal Sur vey Natu ral Re sources In for ma tion and Map ping Cen ter DE PART MENT OF CON SER VA TION Rob ert G. Marv in ney, State Ge olo gist Open- File 98- 122 1998 Re lated Pub li ca tions Dickson, S. M., and Johnston, R. A., 1994, Se bago Lake State Park beach dynam ics: a report on re sults of beach profil ing: Maine Geologi cal Survey, Open File Report 94-4, 189 p. Johnston, R. A., 1998, Shore line classi fi ca ti on of Sebago Lake, Maine: Maine Geologi cal Survey, Open-Fil e Map 98-123, scale 1:24,000. Lewis, E. B., and Johnston, R. A., 1998, Slope stabil ity / shoreli ne classi - fica ti on map of the Songo River, Maine: Maine Geologi cal Survey, Open-Fil e Map 98-124, scale 1:4,000. Ta ble of Content s Page Ab stract ···················································1 In tro duc tion ·················································2 Pur pose···············································2 Ge ol ogy of Se bago Lake ······································2 Shore line Proc esses ········································3 Waves ···········································3 Wind ···········································4 Storms ··········································4 Lake Lev els ········································5 Ice·············································5 Hu man In flu ences ····································5 Cur rents and Long shore Drift·······························5 Meth ods ···················································5 Shore line Clas si fi ca tion ······································5 Beach Pro file Sites ·········································5 Grain Size Data···········································7 Em ery Method of Beach Profil ing ·································7 Plots of Beach Pro files ·······································7 Data Analy sis and Er ror Es ti mates ·································7 Data Cor rec tions ··········································8 Weather···············································8 Ice Ac tion ·············································8 Re sults ····················································8 Shore line Clas si fi ca tion Map····································8 Analy sis of Pro files ········································9 Songo Beach No. 3 ····································9 Songo Beach No. 4 ····································9 Songo Beach No. 5 ···································10 Songo Beach No. 7 ···································10 Halls Beach 11, Tas sel top Park ·····························10 Halls Beach 12, Tas sel top Park ·····························11 Frye Island 2·······································11 Frye Island 3·······································11 Rock wall 7 ·······································12 Rock wall 8 ·······································12 Stan dish No. 1 ······································12 Stan dish No. 3 ······································12 Sand bar 10········································12 Sand bar 12········································12 Har mon Beach, Bar ton Residence ····························13 Har mon Beach, Banks Residence ····························13 Har mon Beach, Straw Resi dence #2 ··························13 Long Point, Sun ning dale ································13 Interannual Trends ········································13 i Re sults (con tin ued) Large Changes, Fall 1996·····································14 Sea sonal Pat terns ·········································15 Beach Fac ing Di rec tion ······································15 Lake Cur rents ···········································15 Beach Dy nam ics ·········································16 Con clu sions ················································16 Rec om men da tions ·············································17 Ac knowl edg ments ·············································17 Ref er ences ·················································18 Fig ures ···················································19 Ap pen dix I - Beach Pro files ········································43 ii List of Fig ures Figure 1. Loca ti on map··········································19 Figure 2. Photo graph of Songo Beach ex posed tree roots. ························20 Figure 3. Beach pro file sites ·······································21 Figure 4. Beach and wave ter minol ogy ··································22 Figure 5. Ide alize d beach profil e adjust m ents to lake level changes ···················23 Figure 6. 1990 wa ter levels ········································24 Figure 7. 1991 wa ter levels ········································25 Figure 8. 1992 wa ter levels ········································26 Figure 9. 1993 wa ter levels ········································27 Figure 10. 1994 wa ter levels ········································28 Figure 11. 1995 water levels ········································29 Figure 12. 1996 wa ter levels ········································30 Figure 13. Fetch map of Songo Beach ··································31 Figure 14. Fetch map of Halls (Tas sel top) Beach ·····························32 Figure 15. Fetch map of Frye Island Beach ································33 Figure 16. Fetch map of Rock wall Beach·································34 Figure 17. Fetch map of Stan dish Beach ·································35 Figure 18. Fetch map of Sand bar Beach ·································36 Figure 19. Fetch map of Har mon Beach ·································37 Figure 20. Fetch map of Long Point (Sun ning dale) Beach ························38 Figure 21. Photo graph of ice carry ing sand and ice bull dozing sand on Sebago Lake ··········39 Figure 22. Photo graph of Spring 1997 ice ridge, Songo Beach ······················40 Figure 23. State of Maine Com prom ise Sebago Lake Plan, 1996·····················41 iii Maine Geo logi cal Sur vey Open- File 98- 122 Beach Dynam ics of Sebago Lake A Re port on the Result s of Beach Pro filing Robert A. John ston Maine Geo logi cal Sur vey 22 State House Stati on Augusta, Maine 04333 Mar tha N. Mixon F. M. Beck, Inc. One Main Street Yar mouth, Maine 04096 AB STRACT Se bago Lake, lo cated in south west ern Maine, is the site of this shore line change study. This study follows up on a previous investigation (Dickson and Johnston , 1994) that re ported on three years of beach pro fil ing at the north end of Sebago Lake. This re port includes an addi tional three years of beach profil ing data at those sites and describes three years of beach pro fil ing at 12 more sites at 6 beaches around the pe rimeter of the lake. The ad di tional sites cover a va riety of compass-faci ng direc tions. In addi tion to beach profil ing, a shoreli ne classi fi ca tion and mapping proj ect was com pleted to de ter mine the types and ex tents of dif fer ent shore line en vi ron ments around the lake; and a moni toring pro gram for erod ing bluffs was initiated. Map ping for the shoreline classi fi ca tion proj ect was done by boat and tape meas ure using 7.5 minute topo- graphic maps as a base. The re sults show the fol low ing types of sur fic ial ma te rials around the pe rimeter of the lake: till (a mixture of sand, silt, and clay), gla cial out wash (sand and gravel), silt, clay, and wetland depos its (silt and de- cay ing plant ma te rial). The shore line en vi ron ment classes mapped are marsh, sandy en vi ron ments (sand beach, seawall behind sand beach, groins with sand in between rip rap, bluffs behind sand beach, and sand beach with boul- ders present), till, arti fi cial fill, and bedrock. Till is the domi nant en viron ment mapped, followed by sand beaches. Two maps pres ent the results of the study: a shoreli ne classi fi ca tion map of Sebago Lake (Johnston, 1998), and a simi lar shore line clas si fi ca tion map showing the Songo River from the Songo Lock to Sebago Lake (Lewis and John - ston, 1998). The bluff ero sion monitor ing pro gram began in the sum mer of 1996, on six erod ing bluffs. Per ma nent mark ers (steel pins) placed at meas ured dis tances along the bluffs were sur veyed with a to tal sta tion and data was collected through the spring of 1997. This pro gram docu mented mi nor ero sion over this short time pe riod, and fur ther moni - tor ing of these sites is rec om mended be cause bluffs tend to re cede episodically. Re sults of beach pro fil ing showed that most beach changes are tran sient sea sonal changes re lated to ice pro - cesses and wa ter level fluc tua tions. Beaches were sta ble over the study pe riod un til the fall of 1996, when the south- facing beaches and one east- facing beach ex pe rienced cata strophic ero sion as a re sult of a com bi na tion of weather events that raised the lake lev els to their maxi mum and later brought high winds out of the south with asso ciated high waves. These large-scale changes are ex pected to be long-last ing. Mi nor ero sion events occurred dur ing spring high water in two years, but were not long-lasting.