Southern Cayuga Lake Watershed Matthew Gonser KEYNOTES: South Cayuga Lake Inlet Complex Creek, Six Mile Creek, and Cascadilla Creek (1) The Lake is an accreting system (Figure 2.2 – The four subwatersheds that feed a. In-stream and channel erosion and the South Cayuga Lake Inlet Complex (hillshade sedimentation is the result of large-scale Watersheds operate at several scales vertical exaggeration 5x)). Cayuga Inlet is the geomorphologic (Figure 2.1.a-c), from large bodies of water second-largest in area, receives flows from processes, a geologic legacy of glaciations and their surrounding environments (1), the Treman State Park and outlets through the Flood b. Human land use practices have historically waterways that flow through them (2), and Control Channel. Buttermilk Creek is the smallest aggravated upland soil erosion contributing the geologic matrix that composes the edges in area, flows through Buttermilk Falls State Park, to sediments in the hydrologic system, a and bottoms of the hydrologic channels (3). and outlets into the Flood Control Channel. Six process known as legacy sediment A watershed is the upslope area that drains Mile Creek is the largest in area, provides the development to a specific point, typically the outlet of a city’s drinking water supply, and is channelized (2) Accretion is a natural process (modified by human stream, river, or lake or the point where a lower activity) and unlikely mitigated through its lower reaches through South Ithaca. order stream meets a higher order stream (3) Continuous sedimentation creates a maintenance Cascadilla Creek is the second smallest in area, issue (Hollingshead, Anderson, and Haith, 2008.). The runs through Collegetown, Downtown, and South Cayuga Lake Inlet Complex is fed by four (4) Sediment in the inlet is a resource: SPOILS SOILS outlets into the inlet at the Farmers Market. (4) subwatersheds: Cayuga Inlet, Buttermilk To understand the process of sedimentation in the Cayuga Inlet system it is necessary to step back, look upstream and consider what the contributors to the system are. Through a watershed approach it is possible to qualify what the hydrologic and material inputs are and ask whether it is possible to prevent the sediments from entering the system, thus reducing the need for dredging maintenance. As found through this investigation sedimentation in the inlet is the legacy of geologic and glacial processes, with contributions from human activity in recent history. These effects are observed today and the ability to influence and/or reduce them is unlikely. Figure 2.1 a Figure 2.1 b Figure 2.1 c Watershed 9 Table 2.1 - Sediments’ potential impact on water resources (adapted: G/FLRPC and EcoLogic, 2001a, Table 3.1.1, p.3-2) Pollutant Impact Sediment: On Fisheries: - From Natural erosion of stream channels, construction, - Decreases transmission of light, which affects plant production urban runoff, gravel operations, agriculture, logging, (food and cover), behavioral activities (nesting, feeding, mating), hydromodification respiration, digestion, reproduction - Increases surface water temperature, which decreases dissolved oxygen concentration in water - Decreases spawning habitat (fills pools and nest sites) - Transports absorbed contaminants On Water Supply: - Damages water treatment pumps, equipment - Increases treatment costs - Reduces reservoir volume - Toxic substances may adhere to sediment - Nutrients increase, which stimulates algae growth - Decreases river bottom infiltration, which reduces well yield On Wetlands: - Reduces flood storage Figure 2.2 - The Four Watersheds that Feed South Cayuga Lake Inlet - Increases peak discharge - Alters habitat On Recreation: Sedimentation – Contributors to the - Decreases clarity of water (public health and safety) South Cayuga Lake Inlet Complex - Reduces aesthetic and recreational value - Reduces sport fishing populations The proximate cause of sedimentation in the inlet system is erosion. Erosion is the process (2010) identified sediment (erosion of stream bottoms by which soils are worn away by wind, water, beds and banks, and not current land use (Figure 2.3 – Diagram of legacy sediment devel- and other natural agents; human activity can practices) as the most-signification non-point opment (Maryland piedmont floodplain develop- aggravate this process. However, the ultimate source (NPS) pollutant affecting Cayuga Lake and ment model. Jacobson, B.D. and Colemen, D.R. cause of sedimentation in the inlet system is its tributary streams. Sediment, as a pollutant, 1986. Figure 7: 635)). They alter and continue to the geologic legacy of glaciations and a period has several impacts on water resources (Table impair the hydrologic, biologic, aquatic, riparian, of legacy sediment development in the recent 2.1): and water quality functions of pre-settlement history of European settlement in the area (ca. The concept of legacy sediments and modern environments (Hartranft, n.d.). 1790). identifies sediment eroded from upland areas The period of greatest legacy sediment The Cayuga Lake Watershed Restoration after and during centuries of intensive land development in Tompkins County occurred and Protection Plan (2001) and the Cayuga Inlet uses. Deposited in valley bottoms along stream between 1790 (i.e., approximate period of major Dredging Project Site Reconnaissance Report corridors, legacy sediments bury pre-settlement European settlement) and 1900. From a 1790 streams, floodplains, wetlands, and valley baseline figure for forest cover of nearly 100%, Watershed 10 Two other major contributors are roadbanks and streambanks (Figure 2.5.a-b – Streambank and roadbank erosion following Tropical Storm Lee, Banks Rd., Six Mile Creek, Ithaca NY (30 September 2011 – Photo: M. Gonser)) . Roadside ditches are sources of sedimentation and erosion. Generally, the closer they are to the lake the more erosion is occurring mainly due to steep gradients from the upland portions of the watershed down to the lake (G/FLRPC and EcoLogic, 2001a, p.14). With the exception of the Buttermilk and Cascadilla 1940 Cover Figure 2.5 a - Roadbank erosion 2011 Cover Figure 2.3 - Diagram of legacy sediment development Figure 2.4 - Canopy cover of South Cayuga Lake area forest cover dropped to 19% by 1900 (Smith, it is predominantly on the steeper lakeside and Marks, and Gardescu, 1993). However, this streamside slopes rather than the flatter uplands percentage increased to 28% in 1938 and 50% by (Smith et al., 1993). Yet, the impacts of the 1980 (Figure 2.4 – Canopy cover of the South historical forest clearance are being felt today, Cayuga Lake area). This fact indicates that the as legacy sediments are transferred downstream majority of forests in Tompkins County today are including the inlet complex, and are mostly post-agricultural, and of these reforested areas irremediable. Figure 2.5 b - Streambank erosion Watershed 11 In the southern tributaries of Cayuga Soil Mass Loading/Wasting Lake, the primary source of sediment appears to be streambank erosion, not runoff from The Cayuga Lake Generalized Watershed construction sites or cultivated fields (G/FLRPC Loading Function Geospatial Database (GWLF) and EcoLogic, LLC. 2001a, p.2). The southern (Haith and Shoemaker, 1987) was designed portions of Tompkins County are generally to quantify factors associated with non-point steeper and less amenable to agriculture. The source (NPS) pollutants in the Cayuga Lake Cayuga Inlet is characterized as very severe and watershed at the landscape scale. The database contains some of the highest stream ranks in the contains information on land use, land cover, watershed (Figure 2.6 – Erosion classification soil characteristics, climate, sewer and septic by subwatershed: Streambank Inventory and systems, impervious surfaces, and topography Average Stream Rank (G/FLRPC and Ecologic, for the entire Cayuga Lake watershed. Focusing 2001a, Map 3.4.3)). Though qualitatively ranked, the model on the four (4) subwatersheds of the is it possible to quantify the material flows Cayuga Inlet system we can extract the following through the South Cayuga Lake Inlet Complex? sediment yield estimates (Table 2.2): Table 2.2 - Sediment yield estimates per subwatershed generated by the GWLF (Haith and Shoemaker, 1987) Subwatershed Sediment Yield Estimates (kg/ha/yr) Area (ha) Buttermilk Creek 49 2942 Figure 2.6 - Erosion classification by subwatershed Cascadilla Creek 40 3451 Cayuga Inlet 91 10,336 Six Mile Creek 54 13,306 Creek watersheds, the southern subwatersheds have numerous road ditches classified as “very Totals 234 30,035 7,028,190 kg/yr severe”. Six Mile Creek roadbanks are areas of concern, with numerous sites documented as moderately eroded or severely eroded. Cayuga Inlet appears to have serious roadbank erosion. G/FLRPC and Ecologic (2001a) found a number of road ditches documented as having moderate or severe erosion problems, and a few very severe sites. Watershed 12 These numbers, though not necessarily equating USDA SSURGO Digital Soil Survey – (2) American However, this model is merely a depicted to sedimentation in the inlet itself, are useful Association of State Highway and Transportation of the susceptibility of land to mass wasting and when considering maintenance and management Officials (AASHTO) soil classification, (3) liquid is not a determination of occurrence. Though regimes in light of the current issue of deferred limit, (4) hydrologic group, (5) physical soil the landslide susceptibility analysis is useful in maintenance, and this and