LANGDON LAKE MCWD H/H and Pollutant Loading Study – 2003 C-1 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion Langdon Lake Table of Contents C. Langdon Lake............................................................................................................................ 3 C.1. General Description............................................................................................................ 3 C.2. Physical Features................................................................................................................ 6 C.2.a. Land Cover/Land Use.................................................................................................. 6 C.2.b. Geology ..................................................................................................................... 10 C.2.c. Soils ........................................................................................................................... 11 C.2.d. Groundwater.............................................................................................................. 11 C.3. Water Quantity ................................................................................................................. 16 C.3.a. Watershed Hydrology................................................................................................. 16 C.3.b. Watershed Hydraulics ................................................................................................ 19 C.3.c. Water Quantity Findings and Discussion................................................................... 19 C.3.d. Watershed Recommendations.................................................................................. 24 C.3.e. Watershed References .............................................................................................. 24 C.4. Scour and Erosion-Prone Areas ....................................................................................... 26 C.4.a. Streams ...................................................................................................................... 26 C.4.b. Lakeshore .................................................................................................................. 26 C.5. Water Quality ................................................................................................................... 27 C.5.a. Watershed Pollutant Load Analysis .......................................................................... 27 C.5.b. Lake Modeling and Associated Goals....................................................................... 32 C.5.c. MPCA Impaired Waters and Point Source Permits .................................................. 38 C.6. Recommendations ............................................................................................................ 39 MCWD H/H and Pollutant Loading Study – 2003 C-2 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion C. Langdon Lake C.1. General Description The Langdon Lake watershed is located along the western boundary of the MCWD and within the cities of Minnetrista and Mound (Figure IV.C.1-1). The watershed is 1055 acres (about 1.6 sq. miles), and includes five subwatershed units (designated LL-1 through LL-5). Figure IV.C.1- 2 shows the subwatersheds and their drainage configuration. Langdon Lake (LL-5) is located at the downstream end of the watershed and is the last in a string of water bodies (Figure IV.C.1-2). On the western end of the watershed, runoff is first received by Black Lake (unofficial name, DNR ID 27-183W) (LL-1) before discharging into Saunders Lake. Saunders Lake (LL-3), receiving flow from both LL-1 and LL-2, is allowed to discharge through a berm into a small creek carrying flows towards Langdon Lake. The creek passes under West Edge Boulevard where runoff from subwatershed LL-4 is received before flowing into Langdon Lake just past the former Mound Wastewater Treatment lagoon. Langdon Lake outlets directly into Lost Lake before entering Cooks Bay of Lake Minnetonka. MCWD H/H and Pollutant Loading Study – 2003 C-3 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion !"110 Minnetrista RT 8 RT 6 !"15 Black Lake Mound !"110 Langdon Lake !"125 Saunders Lake !"44 !"110 Subwatershed Boundaries Major Watershed Boundary Major Roads City Boundaries Streams Lakes 0.2500.25Miles N Figure IV.E.1-1 Langdon Lake Watershed Political Boundaries H&H Report/Basins/Projects/flow_030609_kl MCWD H/H and Pollutant Loading Study – 2003 C-4 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion Black Lake LL-4 LL-5 LL-1 LL-2 < < To Cooks < Langdon Lake Bay via Lost Lake < < Saunders Lake LL-3 < Flow Direction Subwatershed Boundaries Major Watershed Boundary Streams Lakes 0.2500.25Miles N Figure IV.C.1-2 Langdon Lake Watershed Flow Direction H&H Report/Basins/Projects/flow_030609_kl MCWD H/H and Pollutant Loading Study – 2003 C-5 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion C.2. Physical Features The following sections detail the MLCCS, geology, soils, and groundwater of the Langdon Lake watershed. C.2.a. Land Cover/Land Use For comparison purposes, the various MLCCS land cover classifications have been combined into five impervious surface area categories and six vegetative cover type categories (Figures IV.C.2-1 and IV.C.2-2). Although not shown here, each of the impervious surface area categories was further broken down with respect to type of land use and vegetative cover found on non-impervious surface areas. A more detailed map showing MLCCS cover types to Level 3 for the entire MCWD is included in Appendix 3 (Figure IV.Appendix.3-1). A description of all MLCCS cover types is also included in Appendix 3 and is incorporated into the District's interactive GIS tool. Land use in the watershed changes dramatically across the political boundary between the cities of Minnetrista and Mound. Open space in the form of woodlands, forests, grasslands and maintained natural areas dominates the western portion of the watershed that lies within the City of Minnetrista. The Dakota Rail line that divides the watershed into north and south sections hinders connectivity between natural areas in this portion of the watershed. The eastern part of the watershed is dominated almost entirely by residential land use types. Single family residential land use surrounds Langdon Lake to the south and north. To the east the lake is surrounded by commercial and institutional land use. Currently in the Langdon Lake watershed, forests and woodlands, lakes and open water wetlands, and “26% to 50% impervious cover” dominates the landscape, with each of these categories making up approximately 20% of the landscape. Under 2020 land use conditions, lakes and open water wetlands is the most dominant category, with “11% to 25% impervious cover” (18%), and “26% to 50% impervious cover” (19%) close behind. The biggest percent MCWD H/H and Pollutant Loading Study – 2003 C-6 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion increases (Table IV.C.2-1) were in the “0% to 10% impervious cover” and “11% to 25% impervious cover,” categories. The biggest percent decreases were found in agricultural land, forests and woodlands, and grasslands. MCWD H/H and Pollutant Loading Study – 2003 C-7 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion Major roads Subwatersheds Surface water DUTCHDutch !"15 !"15 -MLCCS analysis performed in 2002. Langdon -More detailed MLCCS information can be found in Appendix 3 of this volume. !"12 5 Minnesota Land Cover Classification System 0% to 10% impervious cover 11% to 25% impervious cover 26% to 50% impervious cover !"110 51% to 75% impervious cover 76% to 100% impervious cover Agricultural Land Forests & Woodlands 44 Grasslands !" Lakes & Open Water Wetlands Maintained Natural Areas Wetlands 1000 0 1000 Feet Figure IV.C.2-1 N Langdon Lake Watershed Minnesota Land Cover Classification System H&H Report/Basins/painter_langdon.apr__030221_aps MCWD H/H and Pollutant Loading Study – 2003 C-8 Emmons and Olivier Resources, Inc. Volume IV: Watershed Modeling and Discussion 250 200 Langdon Lake Watershed Land Cover 150 Area [acres] Figure IV.C.2-2 100 Existing Conditions 2020 Conditions 50 0 0% to 10% impervious cover MCWD H/H and Pollutant Loading Study – 2003 Emmons and Olivier Resources, Inc. 11% to 25% impervious cover 26% to 50% impervious cover 51% to 75% Impervious Cover 76% to 100% impervious cover Agricultural Land 20% Forests & Woodlands 15% Land Cover Category Grasslands 10% Lakes & Open Water Wetlands Maintained Natural Areas 5% Percent Watershed Area Wetlands 0% Volume IV: Watershed Modeling and Discussion C-9 Table IV.C.2-1 Langdon Lake Watershed Land Cover Percent Change Percent Change Land Cover Category (from existing to 2020 conditions) 0% to 10% impervious cover 305% 11% to 25% impervious cover 81% 26% to 50% impervious cover 0% 51% to 75% impervious cover 0% 76% to 100% impervious cover 0% Agricultural Land -17% Forests & Woodlands -43% Grasslands -60% Lakes & Open Water Wetlands 0% Maintained Natural Areas 0% Wetlands 0% C.2.b. Geology The St. Lawrence-Franconia Formation is the uppermost bedrock unit within most of Langdon Lake watershed. The Jordan Sandstone is present in the southeastern portion of the watershed, but is eroded away in the north and west. The Quaternary deposits are associated with the Des Moines Lobe glaciation.