Observations on Surface Water in the Seminary Fen in Spring, Prepared 6/4/13 by Sam Wetterlin; updated 7/28/13

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Observations on Surface Water in the Seminary Fen in Spring, 2013 Prepared 6/4/13 by Sam Wetterlin; updated 7/28/13 Ordinarily, a calcareous fen is primarily dependent on upwelling mineral-rich,

1 Observations on Surface Water in the Seminary Fen in Spring, 2013 Prepared 6/4/13 by Sam Wetterlin; updated 7/28/13 Ordinarily, a calcareous fen is primarily dependent on upwelling mineral-rich, oxygen-poor groundwater to maintain a water table near the surface, thereby affecting the types of vegetation that will dominate the fen. In the case of the Seminary Fen (specifically, the Seminary Fen SNA), portions of the fen are actually quite dependent on snow melt and precipitation to maintain the necessary water levels. Likewise, Assumption Creek, which originates in a fen west of the Seminary Fen SNA and then flows south of the Seminary Fen and then through the Seminary Fen, relies heavily on surface runoff from the fen areas to supply its water. Therefore, the response of the Seminary Fen to springtime snow melt and precipitation is of great interest. This document presents some observations on those matters for the spring of Background To evaluate the information presented here, it is important to know how the precipitation in the Seminary Fen in spring, 2013, compares to normal. Figure 1 shows cumulative precipitation in Chanhassen through June 2, 2013: Figure 1 Cumulative 2013 Precipitation per Chanhassen Office of NWS Precipitation was nearly normal through the first week of April, but after that point it became far above normal, mainly due to heavy rains in mid-april and mid-may. After mid-may, the rate of rainfall was about normal, so by June 3 we would expect the creek to be at a normal or slightly above normal level, since the creek adjusts fairly quickly to precipitation levels. We would expect the fen to be above normal wetness after mid-may, since water accumulates quickly and drains relatively slowly from the fen. Assumption Creek We first examine the water levels in Assumption Creek, which at one time was a legitimate trout stream. (It is still officially a fantasy trout stream.) Bottom line, the creek today does not have sufficient flow to continuously flow through the farm fields (the High Terrace property) through which it must flow to get from the western fen in which it originates into the Seminary Fen. That insufficiency is due in part to reduced runoff from the western fen and in part to reduced groundwater levels under the creek, which in turn relates to reduced groundwater levels in the Seminary Fen. 1

Figure 2 shows a combined aerial photo/diagram of Assumption Creek, which continues south from the lower right corner until it reaches the Minnesota River.

Groundwater levels under the yellow area heavily affect the amount of infiltration of creek water, and therefore affect whether the creek can make it to the Seminary Dam at the east end of the yellow

As far as could be determined, the creek reached the dam in the spring of 2013 only twice, once during the April snow melt and once after the heavy mid-may rains.

2 Figure 2 shows a combined aerial photo/diagram of Assumption Creek, which continues south from the lower right corner until it reaches the Minnesota River. Figure 2 Path of Assumption Creek The yellow area of the creek is of primary interest here. In that area, it is flowing through sandy soil lying south of the Seminary Fen. Groundwater levels under the yellow area heavily affect the amount of infiltration of creek water, and therefore affect whether the creek can make it to the Seminary Dam at the east end of the yellow area, and then to the perennial flow area further east. As far as could be determined, the creek reached the dam in the spring of 2013 only twice, once during the April snow melt and once after the heavy mid-may rains. But the total flow over the dam lasted for at most a couple of days. The period of flow was so short that I never actually witnessed it, but there were indirect signs of brief flow over the dam. The first major event of spring is the snow melt, which has potential to create continuous flow in the creek because frost limits infiltration. However, even the frost had limited effect. Figure 3 shows the creek level where it flows out of a culvert under the farm road crossing, located just under the word Dry in the yellow area of Figure 2. 2

Figure 3-Farm Road Crossing, 4/22/13 and 5/6/13 In April, there was a significant pool of water at the culvert outlet, due in part to frost levels that were about 2.

Even when the April 22 photo was taken, the creek disappeared well below reaching the Seminary Dam, as shown in Figure 4.

3 Figure 3-Farm Road Crossing, 4/22/13 and 5/6/13 In April, there was a significant pool of water at the culvert outlet, due in part to frost levels that were about 2.5 deep under the wet area of the creek. By May, the frost directly under the creek disappeared and the water level dropped. Even when the April 22 photo was taken, the creek disappeared well below reaching the Seminary Dam, as shown in Figure 4. Figure 4 Terminus of the flow entering from the west on 4/22/13 Figure 4 looks upstream; there was slight flow which terminated in the debris at the bottom. Even after an extremely wet May (see Figure 1), the creek could not maintain its flow and did not even reach the farm road near the west end of the yellow area in Figure 2, as shown in Figure 4. Figure 5 No Flow at Farm Road Crossing 3

4 There was no flow whatsoever in Assumption Creek at this point, so I looked further upstream. Figure 6 shows what I found. Figure 6 Assumption Creek Near its Endpoint, 6/3/13 Flow at ripples is toward top in small channel 6 wide and 1 deep Figure 6 shows that Assumption Creek ran dry well west of the farm road crossing on the High Terrace property, dwindling to a tiny stream flowing into a small pool where there remaining water infiltrated. The Fen We will focus on the portion of the Seminary Fen lying north of the High Terrace farm fields, because that is the portion where there are the most questions about water levels. The fen in this area seems to derive most of the water in the top several feet of soil from precipitation, rather than from groundwater flow, so the response to springtime runoff is of great interest. (In areas of the Seminary Fen where groundwater is more important, that groundwater ultimately derives from precipitation elsewhere, but the response of groundwater levels to spring precipitation would normally involve a considerable delay.) One interesting discovery was that frost levels within the fen remained within a few inches of the surface in many areas into early or mid-may, which creates more runoff than one might expect. Areas where water persists on the surface, such as pooled areas within the fen, or flowing areas of the creek during the snow melt, lost their frost much earlier. Figure 7 shows a summary of the wetness of various areas during the spring of

Figure 7 General Drainage Areas Colors indicate wetness; letters are for later reference Surface drainage in this area of the fen generally runs to the south or southeast, but there are several

5 Figure 7 General Drainage Areas Colors indicate wetness; letters are for later reference Surface drainage in this area of the fen generally runs to the south or southeast, but there are several elevated areas that interrupt such flow. Those areas are outlined in black and colored brownish/yellowish. These include the High Terrace farm field to the south, the Regional Trail to the northeast, the long-ago abandoned railroad bed that runs parallel to the trail, and a north-south cartway just right of center in Figure 7. Of these, the cartway is the least elevated, and is irregular enough that it does not provide a complete barrier to surface flow. The others are absolute barriers. At location x, there is what appears to be an old culvert or perhaps drain tile running under the abandoned railroad bed, but it appears to be collapsed or plugged. Dark blue areas in Figure 7 contained largely continuous pools of water for much of the spring. They are located where runoff collects at the edges of the elevated areas. The springtime water table in these areas is at or slightly above the surface. Teal-colored areas were very wet, but did not have broad pooling. Rather, they contained a significant number of unconnected small pockets of surface water, generally in the depressions between hummocks. The water table in the teal areas is also likely at or near the surface in spring. Green areas were generally dry and firm at the surface, perhaps with occasional pockets of trapped surface water. Water table levels in these areas in the spring vary from slightly below the surface to several feet below the surface. Uncolored areas in Figure 7 either were not explored or had characteristics intermediate between adjacent colored areas. In addition to classifying colored areas by wetness, we describe three geographical areas. In Area A of Figure 7, surface water does not enter from the north/northwest due to the Regional Trail, and cannot exit to the south/southeast due to the farm field and abandoned railroad bed. Local runoff therefore gathers along the farm field and some sections of the abandoned railroad. There is enough slope that areas that don t pool remain relatively dry at the surface. 5

In Area C of Figure 7, a significant portion of the fen north of the drainage basin near the farm field is quite dry.

6 In Area B of Figure 7, runoff pools against the farm field and against the cartway. The ground slope is gentle enough that, even where water does not pool, much water is trapped in irregularities in the ground. In Area C of Figure 7, a significant portion of the fen north of the drainage basin near the farm field is quite dry. Limited water table measurements were made, but the water table was as much as two feet deep. The blue area where the C label is located was extremely wet in April and May, but began to dry a bit in June. Much of the water appears to come from tile drainage originating to the northwest. The photos in Figures 8 and 9 show the ponding that occurred near the junction of the farm field and the fen. The photos were taken from the long-ago abandoned railroad bed between areas A and B of Figure 7. Figure 8 Pooled area at south end of Area A of Fig. 7, looking west toward the Regional Trail. Farm field is on left. April 22, Figure 8A View to East from Regional Trail in July, Brown area in upper left corresponds roughly to the flooded area in Figure 8. The brown color is due to matured seed on reed canary grass. Figure 8A shows that the flooded area in Figure 8 supports primarily reed canary grass when the flooding recedes. 6

The ponds of both Figures 8 and 9 result from runoff from a considerable area of fen to their north.

7 Figure 9 Pooled area in southwest corner of Area B of Fig. 7, looking east. Farm field is on right. April 22, 2013 The flooded area of Figure 9 also supports primarily reed canary grass later in the year. The ponds of both Figures 8 and 9 result from runoff from a considerable area of fen to their north. (The fen slopes upward to the north, and the frost in the areas north of the pond on this date was generally very near the surface.) The railroad bed blocks any outflow from the pond shown in Figure 8. The general topography would allow the pond in Figure 9 to drain to the east, but the irregularity of the ground surface has trapped this shallow pond. Frost at a depth of 2 feet under the ponds restricts the ability of the water to infiltrate. Interestingly, later in the season these ponded areas are among the driest areas of the fen, with water table levels about 3 feet below ground. With the wetness of spring, one might expect that there would be increased upwelling of water in the area of the Fountain. Figure 10 shows that in fact the area of the Fountain looks pretty much as it normally does, with standing water but only a small amount of outflow. Figure 10 The Fountain, located just off lower right of Figure 7. April 22,

The hydrologic service area (HSA) for this office covers Central Kentucky and South Central Indiana.

The hydrologic service area (HSA) for this office covers Central Kentucky and South Central Indiana. January 2012 February 13, 2012 An X inside this box indicates that no flooding occurred within this hydrologic service area. January 2012 continued the string of wet months this winter. Rainfall was generally