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Monitoring and Modeling the Effect of Agricultural Drainage and Recent water Article Monitoring and Modeling the Effect of Agricultural Drainage and Recent Channel Incision on Adjacent Groundwater-Dependent Ecosystems Philip J. Gerla Harold Hamm School of Geology and Geological Engineering, University of North Dakota, 81 Cornell Street, Stop 8358, Grand Forks, ND 58202-8358, USA; [email protected]; Tel.: +1-701-777-3305 Received: 8 February 2019; Accepted: 20 April 2019; Published: 25 April 2019 Abstract: Channel incision isolates flood plains, disrupts sediment transport, and degrades riparian ecology. Reactivation and periodicity of incision may affect the water table and hydrological conditions far beyond the stream margin. Long-term incision and its recent acceleration along Iron Springs Creek, North Dakota, USA, has affected adjacent ecosystems. An agricultural surface drain empties directly into the original spring-fed source of the creek, which triggered channel erosion both up- and downstream. Historical maps, recent LiDAR, and field surveying were used to characterize incision since ditch excavation in 1911. Although the soils are sandy, small hydrological gradients impede natural drainage in the surrounding stabilized dunes. Incision resulting from expanded drainage and increased precipitation has been as much as 5 m. Numerical models of lateral groundwater profiles corroborated with field measurements show that the nearby water table responds quickly, becoming deeper and less variable. With 1 m of recent incision, model evapotranspiration rates are decreased 50% to 15% from the channel margin to 1 km, respectively, and the hydropattern disrupted >1 km. Species diversity is reduced and floristic quality is 25% less near the drain. A near-channel solution to erosion—fencing out cattle—failed to mitigate the problem because a broader watershed approach was necessary. Keywords: erosion; incision; groundwater; MODFLOW; wetlands; drainage; floral quality index FQI; water table 1. Introduction Stream channel incision occurs naturally and under conditions of human-induced land cover change, including excavated agricultural drains that essentially constitute “controlled” incision. Channel deepening can occur as a result of many factors, including climate change [1,2], lowered stream base level [3], flashier stream flow (often following human development and greater runoff)[4], channelization [5], and changes in sediment load [5–7]. Incision triggered by land cover changes can occur rapidly, with unintended consequences, which include the channel being cut off from its flood plain, stream enlargement [8], severe erosion and deposition [9], and the destruction of riparian zones because of reduced flood water and lowering of the water table [10]. This last process can be profoundly deleterious to groundwater-dependent ecosystems [11]. In areas where soils and sediments are characterized by naturally large permeability, the effect of incision on groundwater drawdown can quickly propagate large distances from the stream channel. The deleterious effects may go unnoticed or attributed simply to other unrelated processes because of landscape heterogeneity and a lack of monitoring and quantitative observation. In southeastern North Dakota, fine sandy Late Pleistocene sediments underlie the watershed of Iron Springs Creek (Figure1). Abundant springs and seeps discharge groundwater along the margins of Water 2019, 11, 863; doi:10.3390/w11040863 www.mdpi.com/journal/water Water 2019, 11, 863 2 of 21 theWater Sheyenne 2019, 11, x River valley, where the river during the last 10,000 years has eroded through the fine2 sands of 22 and cut down into underlying clay till. As the name suggests, Iron Springs Creek was fed by a discrete springthrough before the fine the sands area was and settled cut down and agriculturalinto underlying development clay till. As commenced the name suggests, (Figure2). Iron The Springs creek’s topographicCreek was fed watershed by a discrete expanded spring greatly before in 1911 the when area awas jurisdictional settled and ditch, agricultural Richland Countydevelopment Drain 10,commenced was excavated (Figure and 2). connected The creek's to the topographic creek’s spring watershed headwaters. expanded The hydrological greatly in imbalance1911 when that a ensuedjurisdictional led to ditch, deep erosion,Richland a Co permanentlyunty Drain lower10, was water excavated table, andand subsequentconnected to loss the of creek's Iron Springs. spring Withinheadwaters. the last The two hydrological decades, increasingimbalance precipitationthat ensued led in to the deep region erosion, coupled a permanently with expansion lower water of the drainagetable, and conveyed subsequent into loss Iron of SpringsIron Springs. Creek Within has greatly the last augmented two decades, flow increasing in the original precipitation stream and in uncontrolledthe region coupled headward with migration expansion of incision.of the drainage Erosion conveyed along the channelinto Iron has Springs resulted Creek in the has continued greatly andaugmented expanded flow loss in ofthe groundwater-dependent original stream and unco ecosystemsntrolled headward in the vicinity migration of the of drainincision. and Erosion deeply incisedalong the stream. channel has resulted in the continued and expanded loss of groundwater-dependent ecosystems in the vicinity of the drain and deeply incised stream. FigureFigure 1.1. MapMap ofof thethe IronIron SpringsSprings CreekCreek -- DrainDrain 1010 channelchannel and watershedwatershed within North Dakota's Dakota’s SheyenneSheyenne grassland (insert). (insert). The The blue blue arrows arrows show show the the general general direction direction of groundwater of groundwater flow flow in the in theunconfined unconfined aquifer. aquifer. The The tributaries tributaries to tothe the Shey Sheyenneenne River River and and green green areas areas zone zone indicate indicate major major springssprings andand seeps, seeps, with with the the large large spring spring symbol symbol showing showing the the location location of formerof former Iron Iron Springs. Springs. The grayThe rectanglesgray rectangles west ofwest Road of Road 1211 delineate1211 delineate the monitoring the monitoring and modeling and modeling quadrants quadrants for this for study this study (R and (R D areand the D are reference the reference and disturbed and disturbed blocks, blocks respectively,, respectively, as noted as in noted the text). in the text). Water 2019, 11, 863 3 of 21 Water 2019, 11, x 3 of 22 Figure 2. HistoricalHistorical 1:125,000-scale1:125,000-scale topographic topographic maps maps (north (north - 1897 - 1897 Casselton Casselton quadrangle; quadrangle; south south - 1907 - 1907Wyndmere Wyndmere quadrangle) quadrangle) showing showing the location the location of Iron of Springs Iron Springs (near the(near center the ofcenter section of section 19, T147N, 19, T147N,R52W), R52W), Iron Springs Iron Springs Creek, andCreek, the and Sheyenne the Sheyenne River. The River. grid The shows grid U.S.shows Public U.S. LandPublic Survey Land Survey system systemsections sections (approximately (approximately one square one square mile) within mile) within Township Township 135 North, 135 North, Range Range 52 West 52 and West Range and Range53 West. 53 West. 1.1. Objectives 1.1. Objectives This report describes the case study of Iron Springs Creek and Drain 10 that shows how This report describes the case study of Iron Springs Creek and Drain 10 that shows how unintended consequences of drain excavation, stream incision, and headward erosion can strongly unintended consequences of drain excavation, stream incision, and headward erosion can strongly alter groundwater-dependent ecosystems that lie laterally outward from even a small and ephemeral alter groundwater-dependent ecosystems that lie laterally outward from even a small and waterway and channel. Objectives of this study include: (1) show how groundwater monitoring and ephemeral waterway and channel. Objectives of this study include: (1) show how groundwater modeling can portray hydrological conditions that have been disrupted by drainage and channel monitoring and modeling can portray hydrological conditions that have been disrupted by drainage incision, (2) describe how these disturbances alter plant communities at distances far beyond those and channel incision, (2) describe how these disturbances alter plant communities at distances far generally considered to be the channel’s riparian zone, and (3) outline methods to forecast the extent to beyond those generally considered to be the channel's riparian zone, and (3) outline methods to which the seasonally shallow water table and accompanying evapotranspiration may be altered within forecast the extent to which the seasonally shallow water table and accompanying the watershed if headward erosion remains unchecked. evapotranspiration may be altered within the watershed if headward erosion remains unchecked. 1.2. Description of the Study Site 1.2. Description of the Study Site The Sheyenne grassland of southeastern North Dakota (Figure1) covers roughly 55,000 ha and overliesThe Sheyenne Late Pleistocene grassland of delta southeastern and lake underflowNorth Dakota sediments (Figure that1) covers formed roughly within 55,000 glacial ha Lake and overliesAgassiz [Late12]. ElevationsPleistocene range delta from and aboutlake 290underflow m in the sediments lower Sheyenne that formed River valleywithin to glacial 350 m inLake the Agassizcenter of [12]. the Elevations grassland (Figurerange from S1).
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