Examining wetland loss and potential restoration opportunities in the Sandusky watershed, Ohio


Published on

Methodology for a GIS-based wetland function assessment

Published in: Technology
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide
  • Welcome and thank youToday, take a look at how to use a geographic information system To accurately and quicklyAssess the functions of wetlandsIn a watershed
  • Original task order from EPA, focus of larger project Great Lakes Basin, starting with a small watershedSandusky watershed, northern Ohio“Use landscape modeling techniques to identify opportunities to restore, create and enhance wetlands”Examining wetland loss Identifying potential restoration opportunitiesGoal TODAY is to understand how, in general, the GIS-based landscape modeling method works and why it’s important
  • Framing and perspectiveFirst, WHERE is the AREA that are we talking about todayWhyWhy does this AREA matter,(then, WHY talk about WETLAND FUNCTION for this area)Great Lakes regionGreat Lakes Regional Collaboration (GLRC), 2004, protect, restore regionGreat Lakes Restoration Initiative (GLRI) – 2010 to 2014, created by GLRC“Restoring and enhancing wetlands to improve water quality and water quantity”We need to test one area first, see if it offers benefit to the basin
  • SizeAbout 1800 square miles (1,827 square miles)USGS HUC 8, the Sandusky subbasinTerm “watershed” used to broadly describe family of hydrologic unit boundary names or to talk in general about a specific hydrologic unit (“the Sandusky watershed”)Usesubbasin or watershed interchangeably during talkDrainages, major riversLocated on Lake ErieMost prominent drainage is Sandusky RiverDrains to Sandusky Bay
  • Predominantly agricultural and urbanCitiesSandusky, Fremont2012Population: around 258,000 Only counting five main counties that span watershed (258,022: 60,150 Sandusky County, 76,398 Erie County, 56,018 Seneca County, 22,607 Wyandot County, 42,849 Crawford County)
  • Thank you SantinaFirst I will talk about creating the interpretation of historic wetlandsThen I will move into the specific GIS stepsTo find wetland functions in both historic and current day wetlandsSo, Historic wetlandsIf we want to quantify loss of wetland function in watershedNeed some way to compare CURRENT functional analysis to a PREVIOUS pointIdeal comparison is natural state of watershed, prior to:wide-scale agricultural modifications, deforestation, roadway construction, and hydromodification, such as canals, ditches, reservoirs, as well as municipal storm sewer systemsAnd, that starting point needs to be interpretedWhich we did in a GIS
  • That starting point of comparison in Ohio is generally taken to be around the late 1700sSometimes called “pre-European settlement” conditions, or more generally the term historic wetlands is usedThe goal was to create a GIS layer that was directly comparable to the main wetland database of todayThat main database being the Fish and Wildlife Service’s National Wetlands Index or NWIWhich we will take a look at here shortlyWe want our pre-historic wetland database to be similar in form and function to that NWISo that we can perform the same GIS analysis stepsSo, our starting point for comparison is around the late 1700And for that, we used the work of RB Gordon from 1966His map of the “Original vegetation of Ohio at the earliest land surveys”That map was digitized by ODNR for use in GIS, 2003From that vegetation map, We designed a crosswalk correlation between current day wetland vegetativeclasscodes - - the same codes that are in the NWI - - and the historic vegetation typesYou can see those different vegetation types represented in the map to the left as different color patchesThen we assigned those vegetative class codes to the historic vegetation polygons in the GISWhat we were trying to do is represent the potential types of wetlands that COULD have been present in areas of hydric soilsSecond step, we obtained data from the National Resources Conservation Services soils database, commonly known by it acronym SSURGOSpecifically, the polygons of current-day hydric soils in the SSURGO databaseWe created a crosswalk correlation, between those hydric soil types and the water regime codes in the current day NWIThen we assigned those water regime codes to the SSURGO database polygons in the GISLastly, we needed a dataset to represent historic hydrologyIn the absence of digitized historic maps of rivers, streams, lakes, and pondsWe used the USGS’ National Hydrography Dataset and took out artificial waterbodies, like impounded lakesIf you had historic maps of waterways, either digitized or the time to digitize, you could use thoseSo, taking these three pieces of data…
  • …We combined them in the GIS And created a new historic wetland database, similar in form and functions to the NWIIn the diagram to the left you can see the blue of the interpreted historic wetlands, overlain on top of one of our primary data layers, the historic vegetation mapTo the rightIs an illustration to show you conceptually what is meant by combining those data layersIn the top are visualizations of the historic vegetation[THIS BLUE AND GREEN]And then the hydric soils from the NRCS SSURGO database[THIS LIGHT BROWN]When overlain, as you see at the bottomThat intersection becomes, in this example, two different types of wetlandsSOThis historic wetland map Becomes our starting point To perform the same wetland function analysis that we used on the current-day wetlandsLater in the presentationI will show you the results of that functional analysis, but first Let’s take a look at few more views of the created historic wetland databaseAnd, let’s test and see if we believe the pattern of historic wetlands we created
  • Here isAnother view of the wetlandsWithout the vegetationOverlain instead on topography, in the form of a Digital Elevation Model or DEMNote thatWetlands cluster in the northern section of watershedIn the flat lowlandsAnd then in the rougher highlands to the southThere are smaller patches of interpreted wetlands
  • And, here we are looking at the modern wetlands from the NWI, in orange, superimposed on historic wetlandsThere’s an apparent substantial lossIt’s about a 78% reductionWe go from around 192 thousandDown to 38 thousand acresLet’s lookat some more specific numbers of those results of the comparisonBetween historic and current-dayIn this table…
  • … Here we see The details of the comparisonAs I said, here’s the bottom lineA greater percentage of the Sandusky watershed’s acreage was wetland prior to European settlementAnd here’s our78% loss in wetlands overall, That number includes open-water wetlandsIf you look at just vegetated wetlandIt’s an 81% loss overallThis is Unsurprising and to be expected due to increases in agriculture and developmentThe primary loss of acreage was observed in forested wetlands, And a similar loss in scrub-shrub wetlands. Those wetlands were replaced by emergent wetlands
  • So, to return to this patternof distribution for historic wetlands across the watershedWhen we first ran it, we asked, do we believe this pattern?Is it a good starting point for our comparison?Note thatThere is a sharp line between historic wetlands in the north and sparse wetlands to southAnd we wanted to know what might cause these patches of wetlands in the southWe wanted to validate the interpretation, so I looked to compare results to other physiographic data
  • TO do that, I sought out information on the overarching physiographic provincesof OhioHere is a figure from Ohio Division of Geologic Survey,published 1998It shows the physiographic provinces of Ohio:Physiography,of course,being the characteristic geomorphology orshape of landformsAnd those landforms often have A specific subsurface rock typeOR are related to a specific geologic structureLet’s zoom in on our study area in this physiographic map…
  • … note these three colors hereBlueTeal-greenPale blue patches within tealAnd, also, note this dividing line between the blue and teal-green, just south of Sandusky BayThe blue province here to the north and west of this lineIs the area where the ancient Lake Maumee from geologic pre-history was locatedAnd the teal to the south of lineIs glacial till from the last glaciationAnd, the blobs are isolated ancient lake sediments of a similar age to Lake Maumee within the glacial tillThis lineis the Columbia Escarpment, Marks the join of the western edge of Columbus and Delaware Limestoneshere and ancient Maumee Lake sedimentsWhen we take those boundaries…
  • …And superimpose them on our historic wetlandsAs well as the Pre-European settlement vegetation for referenceWe see that the northern cluster of wetlands is located within the ancient lake sedimentsSeems logical, that hydric soils from the bottom of lake in a lowland area would do a good job of supporting wetlandsAnd, the rocky till to the south is not as likely to support wetlandsExcept for where there are isolated lake sedimentsSimilar to those here in the northNot a perfect match to the location of isolated lake sedimentsFrom the physiographic mapBut, that map is a coarse representationAnd the agreement seems close enoughAlso, it makes senseThat there are not as many wetlands HEREon the east in an area of limestone bedrockSo, this appears to be a reasonable, valid interpretation, that seems to match the natural world
  • OKAYNow that we have our historic wetland database, let’s talk about our current day wetland databaseI am going to show you the GIS steps necessary to arrive at a functional assessment of wetlandsFirst before we get to the functional assessmentWe need to add additional information to these two datasetsRemember, there were two steps under the GIS assessment of wetland functionsOne was Enhancing the National Wetlands InventoryAnd two was then Assigning and Mapping Wetland FunctionsSo, first we will talk about enhancing the NWIBy adding new, additional hydrogeomorphicdescriptorsAnd, we will perform the same stepsTo our historic wetlands databaseSo that we can compare the two datasetsTO THE LEFTIllustration of the FWS website where you can obtain NWI dataSOI will describe what I mean by hydrogeomorphic here shortly, but first, some background…
  • Briefly, I want to provide you some framing and potential resources you can look into if you want more examplesThis method of enhancing the National Wetlands Inventory with hydrogeomorphic descriptorsHas been around since the 90s, starting with RW TINERHis original publications defined these hydrogeomorphicdescriptorsAnd, he has kept publishing and refining the techniqueWhich is well-recognized and supportedby the USGS and the Fish and Wildlife ServiceThere are also currentlymultiple other groupsworking on methods to assign these additional wetland descriptors Using a GISAnd, they are also performing it As a first step for assessing wetland functions in a watershed, tooSome of those groups Are listed here…[READ OFF]For this study, we relied heavily on the MDEQ methods and approachAnd if you wanted to look at just one resource, their 2011 report is a good exampleSO, what do we mean by hydrogeomorphic descriptors
  • What we meanA system that provides information about - -where a wetland sits, such as along a river or stream or in a lake basinAs well asHow the wetland is connected to the hydrologic networkAndwhether that wetland is isolated located in the middle of a stream networkor is perhaps the headwatersource of a streamThese descriptors also identify whether a waterbodythat is associated with the wetland is natural or constructed; And gives an idea of the scale of that waterbody.We call this system “LLWW”Landscape Position, Landform, Waterbody Type, and Water Flow Path (LLWW) This is an enhancement to the existing wetland classification systeminherent to NWITo briefly define these one by oneLandscape Position– wetland’s location with respect to topography and how that impacts the wetland’s water source(s)Landform - refers to physical shape of wetland OR the landscape where it is locatedis it sloped,flat, or in a depression, or maybe located in a FloodplainWaterbody type - applies only to permanent and deep,open water habitats; ponds, lakes, rivers; comes directly from information already in the NWIas well as from calculating the acreage of wetlands in the GISAnd thenWaterflow path - type of water associated with a wetland and the direction that water movesThe GOAL is to add these descriptors to the existing wetlands dataAND the historic wetlands that we have createdIn a fast, repeatable, and accurate mannerTO do that, we will use a GIS in order to automate the process and speed it up
  • Let’s talk about why we use a partially automated GIS screening methodology Versus hand-screening the wetlandsHand-screening:Loosely documentedMultiple analystsLong time frame for a medium-to-large projectAll lead to inconsistent decisions and irregularitiesPartial automation with GIS:Implemented by a basic GIS operator Doesn’t require extensive involvement of specially trained interpreters Reduces time burdenHere’s the basic idea of how the method of assigning the LLWW works in the GISLook to see if the wetland polygon - - the shape in the GIS that defines the position and size of the wetlandOverlaps or doesn’t overlap other data layers in the GIS, such as hydrography data, elevation, or soilsAnd, we also define groupings of wetlands To be placed into different LLWW categoriesbased on information that they already possess Such as the data already present in the NWIOr their sizeThese defined groupings of GIS data overlaps and pre-existing informationFormthe basis of our definitionsfor each LLWW descriptorI will show you some of these LLWW descriptors nowHowever, I won’t be showing you each of the LLWW steps in the GIS in detailJust several that are particularly interesting or challenging in the GISAlso, note that the order of the LLWW definition is different from the order in which we perform in the analysisWe don’t proceed from start to finish in the GIS with landscape position-landform-waterbody type-waterflow pathInstead, we work onThe principle of most effort to least effortFor that reason, the analysis starts with LandformThe second of the “L”sSo, let’s look at LANDFORM first
  • Landform - This refers to the physical shape of wetland OR the landscape where the wetland is locatedHere in the table we have the classes within LandformYou can see the groupings and in the middle we define each of those classesOn the right are the results of assigning these to the current day Sandusky wetlands from the NWINote that as we talk about parts of the LLWWI am not going to go in depth about all of the CLASSES within each DESCRIPTORFor Landform,I do want to point outSLOPEandFLOODPLAINWhich I will show examples of their processing in the GISAlso note in the Fringe there is a comment about NWI water regimes F, G, and HThis is some of that data I have been mentioning as “already in the NWI”Let’s take a quick look that what I mean and how we accessed that, and then come back to the SLOPE and FLOODPLAIN steps in the GIS[FLIP FORWARD ONE SLIDE]Let’s take a look at the steps required in the GIS to select wetlands that should be classified with the SLOPEThis category HEREAnd lets see what that “slope raster generated from the OSIP 2.5-foot DEM” actually is…
  • Cowardincodes are a classification systemThat describes the wetland habitatThey are built into the NWI GIS dataHowever, they are lumped into one single string of charactersFor instance, this one, “L2UBGx” which translates to a wetland that is [read frame from slide]We need some of that informationfor instance that WATER REGIMEThis “G”As one of the criteria for LANDFORM, As you saw from the previous table [FLIP BACK TO PREVIOUS SLIDE, SHOW NWI CRITERIA]We want to split this information apart into separate fields To easily use in the GISSo that we don’t need complex logical arguments to sort and query the data from the NWI in the GISTo do that, we created a relatively simple, straightforward script Using the PYTHON language in the GISWhich splits the code into separate columnsON THE RIGHT, IN BACKGROUNDYou can see some fragments from that codeOnce broken apartINTO THESE COLUMNMakes it sort of like an Excel spreadsheetAnd you can you sort and filter for columns in the GIS[FLIP BACK TO PREVIOUS SLIDE TO INTRODUCE SLOPE]
  • …Here are some screen captures and zooms of work within the GISOn the left, we have a Digital Elevation Model - - a DEM - - from the Ohio Statewide Imagery Project, which was a data source for usWe are seeing the bends of a river and floodplainNote the roads and their width, which gives you a sense of scaleWe used that DEM to make a high-resolution percent slope grid Which is what you see on the rightBasically, in the GIS you examine each pixel in the DEM data in comparison to other pixels near itand calculate the changeFrom that calculation you assign a slope to a pixelWe call that new information a SLOPE RASTER, and you can see it HERE ON THE RIGHTNote, that this is not the same area as the DEM on the left, it’s just an example areaAnd, you can see roads and their width for scaleThe bright-white colors are areas of higher slope, and the black areas are lower slopeSo, we use the slope rasterAnd assigned the average percent slope value across each wetland polygonBy taking the average of all the pixelsthat fall within the area of a wetlandTHIS SHAPE HEREWith that attribute attached to each wetland polygonThe assignment of the slope classWithin LANDFORM- which are wetlands with slopes of 5% or greater - - can be performed
  • Let’s look at one more class example from the LANDFORM descriptor categoryAndThat is the FLOODPLAIN classThis one is quite simpleBut it is facilitated by using the GISTO perform itYou look for the coincidence of wetlands within the FEMA-designated 100-year floodplain areasWhich are easily obtained from the FEMA websiteScreenshot of that to the LEFTTo the RIGHT I have a map from the GISAnd the darker blue areas [POINT]are regions that are classified as 100-year flood zonesWetlands that fall within those areas Are grouped into the Floodplain class of the Landform descriptorSO, that’s only two of the CLASSES within the LANDFORM descriptorThe remaining LANDFORM classes Are assigned based on a wetland’s water regimeAs I showed youThat information that is already contained within the NWI dataLet’s move onAnd look at one more DESCRIPTOR in the LL category of LLWWThat of Landscape Position
  • Here are the criteria for theLandscape Position descriptorLandscape PositionVery simply defined, Is the relationship between a wetland and nearby waterbodiesAgain, we are not going to go into great detailFor each class within the Landscape Position descriptorHowever, I will point out that the Lentic class is best performed in the GIS using DEM dataWhich allows you to determine the actual drainage basins of lakes and that waterbody’s area of influence for wetlandsThose details and steps are provided in the larger reportAs well, using a GIS is critical for determining the location of isolated Terrene wetlandsAnd, within the Terrene wetlands classIs a very important subclass of Terrene wetlands,called headwater wetlandsHeadwater wetlands are an important source for streams and riversAnd, the GIS is useful to quickly sort for themInstead of describing and discussing each Landscape class in detail…
  • …Here is an illustration of how they are definedThis visualization helps to show the type of spatial relationships That a GIS can quickly help findYou can see thatThe Lotic River and Lotic Stream classes, Are relatively straightforward, An intersection of hydrography layers in the GIS, Which is found quicklyLentic, as I mentioned, has a few more criteria that should be looked at in the GIS In order to make sure that wetlands near lakes - - - - but not directly on them - - Are correctly assignedAnd, Terrene wetlands, which are seen HERE These isolated wetlands , can also be repidly identified in the GISWe can also see several Terrene headwater wetlands HEREthat are stream sourcesSO, in the GIS this analysis looks like…
  • …This, which is a visual representation of putting everything together for Landscape Position descriptorSeveral things going on here, let’s pick out a fewFirstLotic River and Lotic Stream[ZOOMED IN SECTION][HERE IS A LOTIC RIVER]Outlined in green[HERE IS A LOTIC STREAM]Outlined in yellowThis illustrates not just how direct intersection of the hydrographic lines[LIKE THESE LIGHT BLUE FLOWLINES]But also the proximity of a wetland to BUFFERS[THESE BLUE HATCHED AREAS]That we definedWere used to identify Landscape Position classesThis 500 foot bufferIs meant to represent the influence that a river would have Beyond it’s immediate linear representation in the GISTo constrain that buffer some so as not to blindly assign any wetland within the buffer as LOTIC RIVERWe also pulled in information from the SSURGO soils databaseSpecifically, the flooding frequency attribute for soilsThat comes written into the SSURGO GIS dataWhen you download itIn the GISThose soils with that attribute[LOOK LIKE THESE GREEN SHAPES] These are the soils experiencing frequent or occasional floodingWe defined Lotic River as either intersecting the river hydrography polygons[THESE THICKER DARK BLUE AREAS, LABELED NHD AREA IN LEGEND]Or, within the river bufferAND intersecting the soils that flood frequently or occasionallyHERE AGAIN[GREEN OUTLINE IN ZOOM]Is an example of thatANDHere is one within the river buffer, [RED OUTLINE IN ZOOM][AND ANOTHER UP TOP][AND OFF TO RIGHT]That were not in an area of frequent or occasionally flooded soilsAnd so were classed as TerreneThen, after Lotic RiverLotic Streamis assigned Lotic StreamWas defined as Either the intersection of the NHDflowlinesOR as wetlands that intersect the soils that flood frequently or occasionally[YELLOW OUTLINES IN ZOOM]This usage of soils was done to capture wetlandsThat might have a small stream running through itThat wasn’t mapped in the GISJust to noteIf there was a stream line originating from one of these terrene wetlandsIt would have been assigned as a Terrene headwater wetlandThese light blue outline wetlands in the legendBut, there are No examples in this mapAn example of Lentic wetlands is also not shown on here, but that class also uses a buffer, like Lotic Riveras well as some DEM analysis to make sure that the effect of the lake’s drainage basin is taken into accountSo, Landscape Position is a somewhat spatially intensive problemThat is best automated with a GIS Now, one last LLWW descriptor we will talk aboutOne of the “W”s …and we will move to talking about wetland functions
  • Here we have the criteriafor waterflow pathWaterflow path – is a way of coding the type of water associated with a wetland ANDthe flowdirectionThis looks like a lot of criteria, however…In order to help you to see,I’ve highlighted the4 main classes, Which each have some additional modifiersThose four types, broadly, areOutflowBidirectionalThroughflowand, IsolatedOutflow and ThroughflowGet additional modifiersforIntermittent and Artificial flows
  • Again, the general approach for classifying this descriptorIs best show in an illustrationHere, you can see we are finding intersections between flowlines and wetlandsOutflow, where streams issue from a wetlandAnd, the Intermittent and Artificial types are what they sound likeBidirectional, these are near waterbodies that fluctuate in water levelThroughflow, just what it sounds like, streams and rivers that move through the wetlandAgain, the modifiers of Intermittent and Artificial are what they sound likelastly Isolated, wetlands which are not directly connected to the hydrologic networkTo perform this analysis in the GIS, our primary dataset is…
  • …The USGS National Hydrography Database (NHD) Or “flow lines” as they are sometimes calledDatabase has coding within it for types of waterwaysSuch as If a stream or river isPerennial or IntermittentOR if a waterway isAPipe, a Canal, or a Ditch- - artificialNot as simple as just intersections, thoughNeed to account for groundwater influence,Which TINER specified in his original LLWW definitionsWetlands assigned to the Throughflowwater flow path are defined by - - - - Receiving either surface OR- - ground waterfrom a stream, other waterbody, or another wetland at a higher elevation;- - And, that the surface or ground water passes through that wetland - - and on to another stream or waterbody.To account for groundwater, we used a 200-foot buffer around perennial and intermittent NHD flowlinesJust like the blue hatched buffer for rivers you saw for the Landscape PositionThis simulates groundwater influence, and assigns wetlands near but not intersected by waterway that are actually likely influenced by that waterwayNo buffer selected for pipes, canals, ditchesOne last thing to noteDealing with these linear features in the NHDZOOMED AREAThese are So-called Straightened stream reachesAnd/or Irrigation conveyancesThey are actuallyCoded in the NHD as “streams”Rather than as ditchesand so in this analysis were coded as Throughflowrather than TH ArtificialFuture analysts using this method may want to revisitAnd develop a way of dealing with these, or may determine like we did that the groundwater behavior is relatively similar
  • Okay, moving onto the next part of our GIS analysisNow that we understand the general process by which LLWW descriptors are added to the wetlandsWe can discuss how to map wetland functions using those newly assigned LLWW descriptors,In combination withAgain, information already in the NWI, and as well drawing in and using other GIS dataI will talk about the GIS methods we usedBut first,lets briefly review what a wetland function isAnd, let’s take a look at the list of wetland functions That we selected for this analysis…
  • Here on the left are the specificwetland functions that we usedAnd, on the right is a simple, succinct definition of what we mean by a “wetland function”Many of you are already familiar with this concept, but just to ensure we are all on the same pageWe are talking about processes - - natural, physical, or biological - - that a wetland providesSometimes these are referred to as “ecosystems services”These functions can be a core feature of the wetland that sustain it, or might be incidentalWe talk and use the term function in this analysisBy saying that a wetland has a “high, medium, or low functional significance”Some examples of that in conversation would be :a High functional significance for nutrient transformation ORa Low functional significance for sediment retentionAnd just to wrap up our definition of the significance of wetland functions, let’s talk about that term “significance”
  • The significance of a wetland functionSo, if I say - - alow functional significance for fish habitat Or, a high functional significance for floodwater storageThat term significanceSimply refers to theABILITY and LEVEL of that natural process to occur in comparison to other wetlandsIt’s that “in comparison” part that we need to emphasizeSignificance is a relative measureWe are describing levels of a function that one group of wetlands has in comparison to another. We use the terms “high,” “moderate,” and “low” to talk about those levelsThose terms used without regard to the perceived human value of any wetland function or its benefit to a watershed. As well, there is no particular regulatory standard or limit that “high” “moderate” or “low” must meetAs we see in the last line “High” simply means. . . performing that process at a better and higher rate than other wetlands within the area of analysis.
  • So, how do we define those wetland functions we saw in the list, like nutrient removalA wetland function in this analysis is a combination of Our new LANDSCAPE and WATER data added in the form of the LLWW descriptors…PLUS the NWI’s original VEGETATION and WETLAND TYPE data……Plus, adding in additional data layers in the GIS, such as the USGS’ NHDAnd Soils dataWe combine the presence or absence of those traits and features into categories to represent functional levelsFor instance, as the analyst, you decide which combination of traits from those categories equals a “high” “medium” or “low”Those combinations are determined by the needs and requirements of regulators and watershed planners. And, as well as working from previous examples Here, we relied on the Michigan Department of Environmental Quality’s (MDEQ’s) definitions from their recent wetland function assessmentNext, we will discuss a few examples of functions used in this analysisStarting with the Floodwater Storage function
  • Floodwater storage is the ability of a wetland to detain or delay the effects of floodingIn this table, we can see the criteria selected for the Floodwater Storage functionAs well as results for both the historic and current day NWI wetlands, on the rightIn general, this function dependsprimarily on the size of the wetland as one of its selection criteriaWith the presumption that a larger wetland would have greater floodwater storage capacityFor a size criteria, we decided on a threshold value of .59 acresThis is based on looking at the entire size population of wetlands in the Sandusky watershedAnd finding the median value of wetland size, which was .59 acresLooking at additional criterianaturally, those wetlands along streams and rivers, or that are ponds, are also highly rated for the floodwater functionYou can see the new LLWW descriptors we added, such as “throughflow” or “terrene” Which are mentioned in the selection criteriaExamining the results we can see that the NWI analysisHas a slightly higher percentage of wetlands with a high functional significance for floodwater storageBut, the historic wetland have a significantly higher percentage of wetlands with a moderate functional significance for floodwater storageNow, let’s see what that looks like in a map
  • Here I am showing a map of the northern part of the Sandusky watershedFor current-day wetlandsThis follows the standard color themes that other researchers have used for wetland functions, red is a “high” functional significanceAnd, orange and grey are the “moderate” and “low” functional significance ratings, respectivelyWe will take a look at some historic wetland results shortlyBut next, another function from the analysis That I have chosen to share with you today And that is nutrient transformation
  • Nutrient transformation is the ability of a wetland to perform nutrient uptake or removalAnd, for our purposes here’s a general description of the two ways nutrients can be transformedONE, fluctuation of water table, which increases - - precipitation of minerals And the deposition of suspended particulates, and the nutrients attached to those particulatesAlso, wetting and drying from water table fluctuationincreases the probability of successful completion of the denitrificationprocessWhich removes dissolved nitrogen from waterSECOND, uptake and usage of nutrients by wetland vegetationSOIn our criteria, we rate highly The vegetated wetlandsAndThe wetlands with frequent water level fluctuationsThe analysis results for both the NWI wetlands and the Historic wetlands are provided on the rightWe can see that, across the board, The historic results show a higher percentage of wetlands with a high and moderate functional significance for nutrient removalNow, let’s see what that looks like in the maps
  • Again, I am showing a map of the northern part of the Sandusky watershedFor current-day wetlandsOnce more, the standard color theme that other researchers have usedwith red as a “high” functional significanceAnd, orange and grey as the “moderate” and “low” ratingsWe will take a look at some historic wetland results in a minuteBut first, let’s examine how we can take the results of all eleven (11) of these functions and combine them into a meaningful composite score
  • Here’s what I meanby combining functional significance results into a “composite score”A “total score” for a wetland offers us a way to rank wetlands overall to each otherThe idea is simpleAssign a score of one (1) to low, two (2) to moderate, and three (3) to high functional significance rankingsSum up all of those functional criteria for a wetland, and you have composite score for that wetlandA bottom composite score of eleven (11) and a top score of thirty-three (33) is possibleNow quite quickly you can compare the wetlands to each other and see the highest functioning wetlands across all categoriesLet’s take a look at some of that raw composite score data, and then some maps
  • Not trying to make you blind, I promiseThis is just an example of the raw data for current-day wetlandsStraight out of the GIS, exported from the system’s database after analysisEach line of data represents a wetland polygonNote the top header rowWhich contains the names of our functionsAndIt’s cut off, but out to the left there are a few dozen more columns With identifiers for each wetlandAs well as LLWW descriptorsNWI Cowardin codesAnd other GIS data fieldsSo, let’s just look at a few composite score examplesVery bottom green box highlights a wetland with a composite score of twelve (12), so LOW in all categories except oneAnd, the top green box highlights a wetland with a score of twenty-nine (29), That’s only four away from the maximum, That wetland scored HIGH in eight of the eleven categoriesNow let’s see what some of these results look like in maps from the GIS
  • Focusing on northern Sandusky watershedThese darker wetlands compared to the lighter shaded ones - - - - are performing at a higher level of functional significance- - for a greater number of criteriaNote that the upper limit is 29- - There were no wetlands that scored above 29 throughout the watershed- - In both current day AND historic wetlands, interestingly
  • Here’s some of the historic wetland data I promised youAdditional individual functional significance results for the historic wetlands can be found in the reportBroadly, though, overallThe comparison of historic to modernUnsurprisingly showsThat there was a loss of more highly functioning wetlands There are fewer wetlands And what wetlands there areAre rated lower for functional significance as compared to the historic wetlands.OKAY, soThere’s a problem with this composite scoring approach, thoughAs some of you might already be thinkingSome of these functional criteria are mutually exclusiveAnd, by combining them, we are canceling out our efforts to rank themFor instance, a wetland that is ranked high for functional significance for shorebird habitat, might correspondingly rank low for interior forest bird habitatThey are likely to be mutually exclusive
  • So, to try and focus in only on functions that compliment each otherWe selected several functions that when combined can tell us something more focused about wetlands in the watershedHere, we’ve selected floodwater storage-nutrient reduction-and sediment retentionAnd, we’re looking at historical wetlands hereFor a new composite score - - note the maximum score of 12
  • In comparison, here’s that same composite sub-score, but for current day wetlandsSo, when we look back and forth between these two points in time[Flip back and forth between two slides]What can we say we that have we learned about our management opportunities and restoration targets in this watershed?Here’s a conclusion that we can take from this…
  • …In general, when we sum the scores and observe what wetland types and locations have higher composite scoreswe can conclude thatThe ideal targets for management are:vegetated palustrine and lacustrine, non-open-water wetlandsLocatedin the ancient lake sediments of the lowlands andThat flood occasionally or frequentlyThese types of wetlands are the ones with the highest functional significance scoresAnd, as well,the lowland areas offer the highest density of potential locations for the creation of new wetlandsThose are our ideal candidates for preservation, restoration, and creationAnd can offer the most benefit to Waterquality, quantity, and the potential for nutrientreduction, too
  • …And then taking that comparative historic assessment …and bringing it back into the watershed planAre there more questions to ask, and can you go around the circle again?
  • LENTIC – “wetlands within topographic basin containing lake and influenced by it”Finding limit of a lake’s influenceLake defined as 5 acres or greaterTiner stated,assign limits to lake’s influence based on the physiography and climate of the landscape under analysisSpecifically, wetlands near shoreline periodically flooded by lakeUsed DEM and ArcHydro GIS tools to find drainage basinThen, select wetlands that Are within drainage area of lakeANDAre within 500’ buffer of lake itselfIf short on time or budget, reasonable proxy is to just select wetlands within buffer distance of lake
  • Terrene Intro on why are headwaters important, how do they fit inDiscussing the illustration of finding headwaters on rightTwo things in this slide, one is headwaters, other is lotic river and lotic stream and not missing that classification by using the SSURGO soil dataTiner,important classification criteria for Landscape position lotic river and lotic stream: wetlands periodically flooded by rivers or streams that they are associated withTo find this, used data fromNational Resources Conservation Services (NRCS) SSURGO Soil Survey Geographic databaseAnd in GIS used:Polygons with soil attribute “Flooding Frequency - Dominant Condition” (flodfreqdcd) Indicates expected frequency of flooding at each wetlandDominant Condition = “Frequent or Occasional”Differentiate between the terrene (TE) and the lotic river and lotic stream classes.
  • …This is Waterbody type, and it actually uses information already within the NWIWaterbody type classificationapplies only to permanent and deep,open water habitats; ponds, lakes, rivers; comes directly from NWI Cowardin codes as well as acreage of the waterbody, which can be calculated in the GISRelatively straightforwardCowardin codes, descriptors inherent to NWI“Wetland code splitter” programshort, simple Python language program that splits the merged codes into individual columns for easy sorting in GISThe “Wetland Verification Toolset,” an important pre-processing step for the NWI wetlands data prior to analysis, creates a GIS attribute class called “WETLAND_TY,” short for “wetland type,” and fills in a generalized classification name for each wetland. For the waterbody type classification step, the “Freshwater Pond” and “Lake” wetland types were selected and then further sorted for the 5 acres or greater division of lakes versus ponds. With respect to Cowardin codes, those selected wetlands translate to ones classed as PUBG, PUBF, or PUBK – Palustrine, Unconsolidated Bottom, Intermittently Exposed (G) or Semipermanently Flooded (F) or Artificially Flooded (K), with special modifiers “x” (Excavated), or “h” (Diked/Impounded), or “d” (Partially Drained/Ditched). Note that the NWI Cowardin code special modifier “h – Diked/Impounded” appeared to have been assigned appropriately in most cases, but was absent from a small percentage of wetlands that could be seen in aerial imagery as the result of impoundment. Therefore it is possible that the dammed river valley (LK2) and diked and/or impounded pond (PD2) values are not always correctly assigned for a small percentage of wetlands.
  • Examining wetland loss and potential restoration opportunities in the Sandusky watershed, Ohio

    1. 1. Examining wetland loss and potential restoration opportunities in the Sandusky watershed, Ohi o Methodology for a GIS-based wetland function assessment Santina Wortman, U.S. EPA James Ashby, PG Environmental
    2. 2. Outline of Today’s Topics  Introduction  Watershed Plans and Wetland Functions  Modeling Historic Wetlands  GIS Assessment of Wetland Functions  Enhancing the National Wetlands Inventory  Assigning and Mapping Wetland Functions  Results  Comparing historic and present conditions  Conclusions and Next Steps Introduction
    3. 3. Background & Purpose Today  Based on report “Methods and Results for a Geographic Information System Landscape Model of Wetland Functions in the Sandusky Subbasin” http://goo.gl/reEXoN Introduction
    4. 4. Great Lakes Basin Introduction
    5. 5. Sandusky Watershed  1,827 square miles  USGS “HUC” 8 – subbasin level Introduction
    6. 6. Sandusky Watershed  Predominantly cultivated and urban land  2012 Population around 258,000 Introduction
    7. 7. Improving watershed plans  Using landscape- level wetland functional analysis to make watershed plan more specific  Percentage and type of wetlands and functions are part of complete watershed plan Watershed Plans
    8. 8. James’ starting point
    9. 9. Creating Historic wetlands  How to create and map historic wetlands  Use to:  Visualize loss  Compare historic functions to current conditions Historic Wetlands
    10. 10. Modeling wetlands  Vegetation records  Current soil maps (NRCS SSURGO)  Current hydrologic layers (or historic!) Historic Wetlands
    11. 11. Historic Wetlands Figure from MDEQ, 2011
    12. 12. Modeling wetlands  Wetland model results on a Digital Elevation Model surface  Historic wetlands cluster in north  Isolated patches in south Historic Wetlands
    13. 13. Versus modern wetlands  Apparent substantial loss  A 78% reduction of wetland acreage  From around 192- thousand, down to 38-thousand acres Historic Wetlands
    14. 14. Historic Versus Current Wetlands Historic Wetlands Pre-European Settlement Wetlands Current Wetlands Difference Forested Wetlands 159,485 acres 15,436 acres 90% loss Emergent Wetlands 1,578 acres 11,859 acres 6.5-fold increase Scrub-Shrub Wetlands 16,084 acres 2,484 acres 85% loss Open Water 14,676 acres 8,009 acres 55% loss TOTAL 191,823 acres 37,788 acres 78% loss Total vegetated only 177,147 acres 29,779 acres 81% loss
    15. 15. Validating the model  Do we believe that the distribution of historic wetlands is valid?  Let’s check it against other data Historic Wetlands
    16. 16. Physiographic provinces  Huron-Erie Lake plains – ancient Lake Maumee sediments  Glacial till plains  Isolated ancient lake sediments Historic Wetlands
    17. 17. Physiographic provinces  Huron-Erie Lake plains – ancient Lake Maumee sediments  Glacial till plains  Isolated ancient lake sediments Historic Wetlands
    18. 18. Physiography & wetlands  Distribution pattern of historic wetlands in a physiographic context  Reasonable agreement  Appears to be a valid interpretation Historic Wetlands
    19. 19. Enhancing the FWS’ NWI  How to rapidly and methodically assign hydrogeomorphic descriptors to the U.S. Fish and Wildlife Service’s National Wetlands Inventory GIS data Enhancing the NWI
    20. 20. Origins & previous work  R.W. Tiner, original descriptor keys (1995)  Michigan Department of Environmental Quality (MDEQ) (2011)  Montana Natural Heritage Program (MNHP)  Conservation Management Institute (CMI) Virginia Tech (Long Island, Delaware) Enhancing the NWI
    21. 21. The LLWW descriptors Geomorphic  L andscape position  L andform Hydrologic  W aterbody type  W ater flow path Enhancing the NWI …hydrogeomorphic descriptors
    22. 22. Assigning LLWW with a GIS  Why use a GIS?  Sorting, selecting, and coding wetlands is performed in the GIS, based on:  Whether within or outside of other layers (e.g., Hydrography, DEM analyses, and soils)  Possessing traits already assigned (e.g. NWI water regimes or acreage of wetland) Enhancing the NWI
    23. 23. L andform Slope (SL) Wetlands occurring on a slope of 5% or greater, as indicated by a slope raster generated from the OSIP 2.5-foot DEM 35.66% (3,566 of 10,000 records) Island (IL) A wetland completely surrounded by water, as indicated by the NHD Waterbody layer. Less than 1 percent (36 of 10,000) Fringe (FR) Wetland occurs in the shallow water zone of a permanent waterbody. *NWI water regimes F, G, and H 27.13% (2,713 of 10,000) Floodplain (FP) Wetland occurs on an active alluvial plain along a river and some streams, as defined through the use of FEMA floodplain data. 8.02% (802 of 10,000 FP; 436 FPba, 366 FPfl) Basin (BA) Wetland occurs in a distinct depression. *NWI water regimes C and E 15.2% (1,520 of 10,000) Flat (FL) Wetland occurs on a nearly level landform. *NWI water regimes A, B, and K. 13.63% (1,363 of 10,000) Enhancing the NWI
    24. 24. Cowardin codes  Describes habitat  Built into NWI  Wetland code splitter breaks code into parts Enhancing the NWI NWI_Code NWI_System NWI_SubSys NWI_Class NWI_SubCla NWI_WatReg NWI_SpMod PFO1A P FO 1 A PFO1C P FO 1 C PFO1C P FO 1 C PFO1C P FO 1 C PFO1C P FO 1 C PFO1C P FO 1 C PFO1C P FO 1 C PSS1 P SS 1 C PUBG P UB G PUBG P UB G PFO1C P FO 1 C PFO1C P FO 1 C PUBGx P UB G x L2UBGx L 2 UB G x PFO1C P FO 1 C PEM1C P EM 1 C R2UBG R 2 UB G PFO1C P PSS1 P PUBG P PUBG P PFO1C P PFO1C P PUBGx P L2UBGx L 2 PFO1C P Lacustrine Littoral (near shore) Unconsolidated bottom Intermittently exposed Excavated
    25. 25. Slope – part of Landform Enhancing the NWI
    26. 26. Floodplain – part of Landform Enhancing the NWI  FEMA 100-year flood data
    27. 27. L andscape Position Enhancing the NWI Lentic (LE) Wetland in or along lake (waterbody >= 5 acres) or within basin, defined as area contiguous to lake affected by rising lake levels. Contiguous area of effect found through Arc Hydro GIS analysis. This landscape position type should be analyzed and assigned first. 5.54% (554/10,000) Lotic River (LR) Wetland associated with (directly intersected by) a river or its active floodplain. 7.89% (789/10,000) Lotic Stream (LS) Wetland is associated with (directly intersected by) a stream or its active floodplain. 13.97% (1,397/10,000) Terrene (TE) Wetland that is: 1. Located in or borders pond, or wetland is a pond, (waterbody < 5 acres in size surrounded by upland); 2. Or, adjacent to but is not affected by a stream or river (located in or along, but NOT periodically flooded stream); 3. Or, completely surrounded by upland (non-hydric soils). 72.60% (7,260/10,000, of which 191, 1.91%, are headwater wetlands)
    28. 28. L andscape Position Enhancing the NWI Lentic (LE) Lotic River (LR) Lotic Stream (LS) Terrene (TE)
    29. 29. Enhancing the NWI
    30. 30. W ater Flow Path Enhancing the NWI Outflow (OU) Water flows out of the wetland naturally, but does not flow into this wetland from another source. Less than 1 percent (75/10,000) Outflow Intermittent (OI) Water flows out of the wetland intermittently, but does not flow into this wetland from another source. Less than 1 percent (63/10,000) Outflow Artificial (OA) Water flows out of the wetland, in a channel that was manipulated or artificially created. Less than 1 percent (53/10,000) Bidirectional (BI) Wetland along a lake and not along a river or stream entering this type of waterbody; its water levels are subjected to the rise and fall of the lake levels. Lentic wetlands with no streams intersecting them. 3.48% (348/10,000) Throughflow (TH) Water flows through the wetland, often coming from upstream sources (typically wetlands along rivers and streams). Lentic wetlands with streams running through them are classified as throughflow (or throughflow intermittent, if stream is classed as intermittent). 19.15% (1,915/10,000) Throughflow Intermittent (TI) Water flows through the wetland intermittently, often coming from upstream sources (typically wetlands along streams). 11.02% (1,102/10,000) Throughflow Artificial (TA) Water flows through the wetland, in a channel that was manipulated or artificially created. 1.16% (116/10,000) Isolated (IS) Wetland is typically surrounded by upland (nonhydric soil); receives precipitation and runoff from adjacent areas with no apparent outflow. 63.85% (6,385/10,000)
    31. 31. W ater Flow Path Enhancing the NWI Outflow (OU) Outflow Intermittent (OI) Outflow Artificial (OA) Bidirectional (BI) Throughflow (TH) Throughflow Intermittent (TI) Throughflow Artificial (TA) Isolated (IS)
    32. 32. GIS data – USGS Hydrography layers Enhancing the NWI
    33. 33. Assigning wetland functions  How to define your functions of interest and map the wetlands that provide them Wetland Functions
    34. 34.  Flood water storage  Streamflow maintenance  Nutrient transformation  Sediment retention  Shoreline stabilization  Fish habitat  Stream shading  Bird habitat  Amphibian habitat Natural, physical, or biological process occurring within a wetland – as well as within connected waterways and ecosystems. Processes may sustain and maintain wetland, or may be an incidental function that the wetland provides. Wetland Functions
    35. 35. Defining significance of a wetland function  Significance is a relative measure - - comparison of wetlands to each other  Meant to classify and rank wetlands for ability to perform natural processes  “High” “Moderate” and “Low” - - used without any social/regulatory value or quantitative limits  “High” simply means “performing process at better/higher rate than other wetlands in area” Wetland Functions
    36. 36. How is it performed? NWI Cowardin wetland type designation LLWW hydrogeomorphic descriptors Additional GIS data (soils, NHD) Functional significance selection criteria Wetland Functions
    37. 37. Floodwater Results Functional Significance Selection Criteria Results NWI Historic High Wetlands along streams and rivers Island wetlands Ponds that are throughflow, throughflow intermittent, bidirectional, and isolated and that are = or > 0.59 acres 31.76% (13,175 of 41,489 acres) 21.48% (41,338 of 192,451 acres) Moderate All of the above in the High category that are < 0.59 acres Terrene basin isolated Terrene & outflow or outflow intermittent wetlands Other ponds and terrene wetlands associated with ponds connected to hydrography network Terrene wetlands that are associated with ponds All lake-side wetlands not already ranked high 40.16% (16,661 of 41,489 acres) 64.09% (123,350 of 192,451 acres) Low All remaining wetlands 28.09% (11,653 of 41,489 acres) 14.43% (27,763 of 192,451 acres)
    38. 38. Floodwater storage Wetland Functions
    39. 39. Nutrient Results Functional Significance Selection Criteria Results NWI Historic High Vegetated wetlands from NWI P_ (AB, EM, SS, FO, and mixes) with water regime C, E, F, H, G. No open water types – with SSURGO Flood Frequency of “Frequent” or “Occasional” 10.13% (4,205 of 41,489 acres) 25.37% (48,827 of 192,451 acres) Moderate Vegetated wetlands from NWI P_ (AB, EM, SS, FO, and mixes) with water regime C, E, F, H, G. No open water types – with SSURGO Flood Frequency of “Rare” or “None” (“Very Rare” not found in this data set) Seasonally Saturated and Temporarily Flooded Vegetated Wetlands from NWI P_ (AB, EM, SS, FO, and mixes) with A, B water regime or lacustrine vegetated wetlands (no open water) – with SSURGO Flood Frequency of “Frequent” or “Occasional” 32.11% (13,323 of 41,489 acres) 62.01% (119,339 of 192,451 acres) Low All remaining wetlands 57.75% (23,961 of 41,489 acres) 12.62% (24,284 of 192,451 acres)
    40. 40. Nutrient transformation Wetland Functions
    41. 41. Total composite scores  Gives us a way to quickly compare wetlands to each other  Assign a score of –  three (3) to High  two (2) to Moderate  And one (1) to Low  Maximum of 33  Minimum of 11 Wetland Functions
    42. 42. Composite scores Wetland Functions FloodW_Sto Nutr_Trans Sed_Ret SFlow_Main Shore_Stab Fish_Hab Stream_Sha WaterBird_ ShoreBird_ FoBird_Hab Amphib_Hab TOTAL Composite Score High Low High Low High Moderate Moderate Low Moderate High Low 22 Low Moderate Moderate Low Low Low Low Moderate Moderate High Low 17 Low Moderate Moderate Low Low Low Low Moderate Moderate High Low 17 High Moderate Low Low High High Low Moderate Moderate High Low 22 High Moderate High Moderate High High Low Moderate Moderate High High 27 High High High Moderate High High Low Moderate Moderate High High 28 Low Moderate Low Low Low Low Low Moderate Moderate High Low 16 High Moderate Low Moderate High Low Moderate High Moderate High Low 23 High Low Moderate Moderate Moderate High Low Low Low Low Moderate 19 High Low Moderate Low Low High Low Low Low Low Low 16 Low Moderate Moderate Low Low Low Low Moderate Moderate High Low 17 Low Moderate Moderate Low Low Low Low Moderate Moderate High Low 17 High Low High Moderate Low Low Low Low Low Low Low 16 Moderate Low Low Low Low High Low Low Low Low High 16 High High Low Low High High Low Moderate Moderate High Low 23 High High High Moderate High High Low High Moderate High High 29 High Low Low Low Low High Low Low Low Low Moderate 16 High High Low Low High High Low Moderate Moderate High Low 23 High High Low Low High High Low High Moderate Low Low 22 High High Low Low High High Low High Moderate High Low 24 High High Low Low High High Low High Moderate High Low 24 High High Low Low High High Low High Moderate High Low 24 High Low Moderate Low Low Low Low Low Low Low Low 14 High High Low Low High High Low High Moderate High Low 24 High Moderate Low Low High High Low Low Moderate Low Low 19 High High Low Low High High Low Moderate Moderate High Low 23 High Low Moderate Moderate Moderate High Low Low Low Low Moderate 19 Moderate Low High Moderate Low Low Low Low Low Low Low 15 Low Moderate Moderate Low Low Low Low High Moderate Low High 18 Low Moderate Moderate Low Low Low Low High Moderate Low Low 16 Low Low Low Low Low Low Low Low Moderate Low Low 12 High High Moderate Low High High Low High Moderate Low Moderate 24 High High Low Low High Low Low Moderate Moderate High Low 21 High High Moderate Low High High Low Moderate Moderate High Moderate 25 High High High Moderate High High Low High Moderate High High 29
    43. 43. Wetland Functions
    44. 44. Wetland Functions
    45. 45. Wetland Functions
    46. 46. Wetland Functions
    47. 47. Historic versus current wetlands – the takeaway Ideal targets for wetland management in the Sandusky watershed –  Wetland types  Vegetated palustrine and lacustrine  Non-open water  Located  In lowlands  In geologic pre-history lake sediments  Flood occasionally or frequently Wetland Functions
    48. 48. Full Circle  New questions to ask or watershed plan strategies to consider that may need analysis? Conclusion
    49. 49. Next steps
    50. 50. Acknowledgements  Conversations with members of the Conservation Management Institute (CMI) at Virginia Tech provided insight, as well as the published NWIPlus and LLWFA datasets from CMI’s work with the Delaware Department of Natural Resources and Environmental Control.  The Montana Natural Heritage Program (MNHP) is also in the process of developing a LLWFA methodology and their publications and presentations were a useful resource.  Current Oak Ridge Institute for Science and Education (ORISE) fellowship-funded wetland function research was also instrumental for methodology development.
    51. 51. Lentic – part of L andscape Position  DEM analysis  “ArcHydro” GIS tools  Find drainage basins  Define buffer  Physiography & climate  Lentic assignment Enhancing the NWI
    52. 52. Headwaters – L andscape Position  Headwater streams  Terrene headwater  Periodic flooding  SSURGO data Enhancing the NWI
    53. 53. W aterbody Type Enhancing the NWI Natural Pond (PD1) A natural pond that is less than 5 acres in size. 6.4% (640/10,000) Diked and/or Impounded Pond (PD2) A pond that is diked and/or impounded and is less than 5 acres in size. 4.27% (427/10,000) Excavated Pond (PD3) A pond that excavated and is less than 5 acres in size. 26.17% (2,617/10,000) Natural Lake (LK1) A natural lake that is greater than 5 acres in size. Less than 1 percent (62/10,000) Dammed River Valley (LK2) A lake (greater than 5 acres in size) and created by damming a river valley. Less than 1 percent (40/10,000) Excavated Lake (LK3) A lake that is excavated and greater than 5 acres in size. 1.06% (106/10,000) River (RV) A polygonal feature in the NHD (or Ohio hydrography dataset) or NWI dataset. Less than 1 percent (28/10,000)