TOWARD A WATERSHED MODEL FOR CLEAR LAKE S. Geoffrey Schladow UC Davis Blue Ribbon Committee Meeting Sept. 26, 2019
A distributed watershed model is a computer model that uses sets of mathematical equations to: 1. Simulate hydrologic processes (movement of water) across and through the landscape 2. The accompanying erosion and sediment transport that may occur due to steepness, lack of cover, imperviousness, type of land use etc. 3. The accompanying nutrient transport, uptake and release that is occurring due to different activities, soils, reactions etc.
STEP 1 - Subwatershed Delineation • Subdivision of the watershed into discrete components • Delineation based on: • elevation (topographic data) • stream connectivity • location of flow and water quality monitoring stations • Each subwatershed is modeled with 1 representative stream • Each subwatershed is modeled with 1 representative meteorological time series
Sub-watershed Delineation This is provided by the Lidar data Lake Tahoe from which a Digital Elevation Model (DEM) has likely been produced already Subwatersheds Lake Tahoe Elevation 1889 - 2044 2045 - 2200 2201 - 2356 2357 - 2512 2513 - 2667 2668 - 2823 2824 - 2979 2980 - 3135 3136 - 3291 No Data
The Use of Sub- Watersheds is What Makes it a Distributed Watershed Model N Lake Tahoe 184 Streams Subwatersheds Watersheds 0 1 2 3 4 5 Kilometers
N Step 2 - Land Use Classifications This is provided by Lake Tahoe existing GIS layers, high resolution satellite data, Lidar data etc. Subwatersheds Final Composite Land Use Residential_SFP Residential_MFP CICU-Pervious Ski Runs-Pervious Vegetation-Unimpacted Vegetation-Recreational Vegetation-Turf Waterbody Roads-Unpaved Residential_SFI Residential-MFI CICU-Impervious Roads-Primary Roads-Secondary Lake Tahoe 0 10 20 Miles
LIDAR LiDAR is a remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light.
LiDAR Point Cloud (all LiDAR points) Bare Earth (LiDAR ground points)
“Satellite Survey” Countless uses of satellite data - Weather (from past data) – for watershed model? - Water temperature - - climate change, lake water movement etc. - Algal blooms (cyano and general)
- Step 3 – Determining erosion potential This is based on GIS layers of soil types, ground slope, coverage etc. Produces erodibility classes Erodibility classes 3 1 4 2 0 5 10 kilometers 5
Step 4 - Watershed Model Land-use Categories Landuse Category Pervious/Impervious Subcategory Name Pervious SFR - Pervious Single Family Residential Impervious SFR - Impervious Pervious MFR - Pervious Multi Family Residential Impervious MFR - Impervious Commercial/Institutional/ Pervious CICU - Pervious Communications/Utilities Impervious CICU - Impervious Impervious Primary Roads Transportation Impervious Secondary Roads Pervious Unpaved Roads Pervious Ski Runs Pervious Recreation Pervious Burned Pervious Harvest Pervious Turf Areas Vegetated Pervious Erosion Potential - 1 Pervious Erosion Potential - 2 Pervious Erosion Potential - 3 Pervious Erosion Potential - 4 Pervious Erosion Potential - 5
N Step 5 - Meteorology – this is what “drives” the model MT. ROSE % U SKI AREA Number of Impaired Hours per Day Original Hourly SNOTEL Temperature (Fallen Leaf) Corrected Temperature 80 24 Data Quality (Impaired Hours) Average Temperature (Deg F) 70 21 60 18 50 15 TAHOE CITY CROSS MARLETTE 40 12 U % LAKE U % 30 9 WARD U % CREEK 20 6 Lake Tahoe GLENBROOK 10 3 X ( 0 0 1/1/1995 7/1/1995 1/1/1996 7/1/1996 1/1/1997 7/1/1997 1/1/1998 7/1/1998 1/1/1999 7/1/1999 1/1/2000 7/1/2000 1/1/2001 7/1/2001 1/1/2002 7/1/2002 1/1/2003 7/1/2003 1/1/2004 7/1/2004 1/1/2005 DAGGET RUBICON % U PASS ( X FALLEN HEAVENLY LEAF % U VALLEY U % Tahoe City Reference ET * Reference ET adjusted for Evergreen Forest LSPC Modeled Total ET (10/1996-9/2003) SOUTH LAKE X ( 8 TAHOE AP 7 ECHO % U % U 6 HAGAN'S PEAK MEADOW Inches/Month 5 4 3 NCDC Weather Stations ( X 2 NRCS SNOTEL Stations % U 1 Lake Tahoe Subwatersheds 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec * Historical average monthly reference crop evapotranspiration for Tahoe City, California UC Davis Division of Agriculture and Natural Resources, Publication 21454 0 10 20 Miles
N Step 6 - Calibration and Validation Third Creek This is the hard part. • Incline Creek % U U % # # Y Y Need at least 1 year of meteorological data to • Marlette Creek U % “input” to the model for “calibration”, and at least Ward Creek % # U Y 1 year to ”validate” the model performance. Lake Tahoe U % # Y Blackwood Creek Glenbrook Creek U # % Y U % Y # Logan House Creek Calibration - adjust individual • % U Y # General Creek coefficients for erosion, Edgewood Creek U % # Y Upper Truckee River nutrient release etc. so that at South Lake Tahoe % U # Y Trout Creek U % # Y data from gauging stations Upper Truckee River U % at Hwy 50 match the measured values. TOC % U Upper Truckee River Validation – change nothing, confirm that model • at S. Upper Truckee Road can represent a different set of data LTIMP Water Quality Stations Y # USGS Flow Gages % U Lake Tahoe If insufficient or poor stream data, the results are • Streams Subwatersheds of dubious value - GIGO 0 10 20 Miles
Output - Fine Sediment Loads Load, MT/yr R e s i d e 1,000 2,000 3,000 4,000 5,000 6,000 7,000 n R t i a e l _ s S i d F 0 e P n t i a l C _ M I C F S U k P i - _ P R e u r v n i s o - u P s e r v i o u s V e g _ e p 1 V e Upland Fines, metric tons g _ e p 2 V e g _ e p 3 V e g _ e V p 4 e V g e _ g R _ e e c p 5 r e a t i o V n e a l g _ B u r V n e e g d _ H a r v e s t V e Upland TSS, metric tons g _ W T u a t r e f R r _ e B s i o d d e y n R t i a e l s _ i S d e F n I C t i I a C l _ U M - I F m I p R e r o v a i o d R u s s o _ a P d r s i m _ a S r e y R c o o n a d d a s r y _ U n p a v e d
Output - Phosphorus Loads Load, kg/yr Residential_SFP 1,000 2,000 3,000 4,000 5,000 6,000 Residential_MFP 0 CICU-Pervious Ski_Runs-Pervious Veg_ep1 Veg_ep2 Surface TP, kg/yr Veg_ep3 Veg_ep4 Veg_Recreational Veg_ep5 Veg_Burned Veg_Harvest Baseflow TP, kg/yr Veg_Turf Water_Body Residential_SFI Residential_MFI CICU-Impervious Roads_Primary Roads_Secondary Roads_Unpaved
Output - Nitrogen Loads Load, kg/yr R e s i 10,000 15,000 20,000 25,000 30,000 d e 5,000 n t i a R l _ e S s 0 i F d P e n t i a l _ M C F I C P U S - k P i e _ r v R i u o n u s s - P e r v i o u s V e g _ e p 1 V e g _ e p 2 V e g _ e p Surface TN, kg/yr 3 V e g _ e p 4 V V e e g g _ _ R e p e c 5 r e a t i o n a V l e g _ B u r n V e d e g _ H a r v e s t Baseflow TN, kg/yr V e g _ T u W r f a t e r R _ e B s o i d d y e n t i a R l _ e S s F i d I e n t i C a I l C _ M U - F I m I p e r v R i o o a u s d s _ R P o r i a m d s a _ r y S e c o R n o d a a d r y s _ U n p a v e d
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