Master of Science Practical Exam. Climate and Hydrology of Big Spring Creek, Cumberland County, Pennsylvania

Transcription

1 Master of Science Practical Exam Climate and Hydrology of Big Spring Creek, Cumberland County, Pennsylvania Laurie Young Revised January 27,212- February 3,212 For: Dr. Woltemade Dr. Feeney

2 Table of Contents Introduction 1 Study Area..1 Review of the Literature..2 Introduction 2 Studies using precipitation and spring discharge rates 3 Studies using a water budget.3 Methods...4 Results.4 Analysis of water budget 4 Analysis of daily precipitation and discharge Discussion 18 Conclusion...2 Appendix A... 2 Works Cited..21 List of Figures Figure 1: Illustration of the origin of Big Spring Creek at the boundaries of two formations... 1 Figure 2: Illustration of the relationship between water deficit, surplus, and runoff.5 Figure 3: Illustration of the relationship between average monthly precipitation and calculated potential and actual evapotranspiration... 5 Figure 4: Illustration of the relationship between average monthly precipitation, surplus, deficit and discharge rates 6 Figure 5: Illustration of average daily discharge and precipitation at Big Spring Creek.. 7

3 Figure 6: Hydrograph for June and July Figure 7: Illustration of the relationship between Big Spring Creek s average monthly discharge rates and various calculations for runoff and surplus amounts.8 Figure 8: Illustration of the relationship between runoff and discharge rates for the years Figure 9: Relationship between projected calculated runoff (3/25-11/21) and Big Spring Creeks discharge rates (4/25-12/21) 1 Figure 1: Relationship between calculated runoff and discharge 1 Figure 11: Scatterplot showing the relationship between daily discharge and precipitation for Figure 12: Comparison between daily discharge and precipitation for Figure 13: Relationship between daily precipitation and discharge during a seven day precipitation event Figure 14: Relationship between daily precipitation and discharge during a six day precipitation event.13 Figure 15: Illustration of average weekly precipitation totals and average weekly discharge rates..14 Figure 16: Illustration of the total precipitation and average discharge calculated seasonally..15 Figure 17: Illustration of the six month average in discharge and the six month total precipitation..16 Figure 18: Illustration of the six month total precipitation and average discharge. 16 Figure 19: The average six month discharge and the six month total precipitation...17 Figure 2: The average six month discharge and the six month total precipitation...17 Figure 21: Illustration of total yearly precipitation and average yearly discharge rates for

4 Introduction The purpose of this research is to evaluate the climate and hydrology of Big Spring Creek, Cumberland County, Pennsylvania. The question being asked is can a relationship between Big Spring Creek s discharge and climate data be used to determine future discharge? The objectives are: to asses the weather conditions at Shippensburg, Pennsylvania and develop a predictive relationship between precipitation and discharge rates at Big Spring Creek; to explain the strengths and weaknesses of the predictions; and to explain the details of events or situations for which discharge is poorly predicted by using basic climate data. Study Area Big Spring Creek is located in the Cumberland Valley of south-central Pennsylvania. The Cumberland Valley is part of the Great Valley that extends from New York to Georgia and is part of the Valley and Ridge Physiographic Province (Van Diver, 199). The Cumberland Valley is bordered by South Mountain in the southeast and by Blue Mountain to the northwest. The broad valley is characterized by a sequence of formations with younger layered carbonate bedrock in the southeast and older shale bedrock to the northwest (Lindsey, 25). The valley is made up of features typical to karst terrains which include: closed depressions, caves, sinking springs, springs, and dry channels (Hurd et al., 21). The karst topography in this area is an important factor affecting groundwater flow N (Lindsey, 25). Triassic-age diabase dikes extend north to south throughout the valley and act as groundwater dams and diversions in some locations and many springs discharge at faults or at the contact of dikes (Chichester, 1996). S Figure 1: Illustration of the origin of Big Spring Creek at the boundaries of two formations and direction of flow. Data source: PASDA, USGS Newville, Pennsylvania Quadrangle 1

5 Big Spring Creek originates at the contact between the Shadygrove Formation and the Stonehenge Formation (Figure 1) and flows northward to the Conodoguinet Creek. The Shadygrove Formation is late Cambrian in age and is a light grey micritic limestone with abundant brown chert nodules and includes some sandstone beds and laminated dolomite beds (Becher & Root, 1981). The Stonehenge Formation is early Ordovician in age and is a light grey micritic limestone containing detrital beds and some chert bearing limestone beds (Becher & Root, 1981). Big Spring Creek receives most of its discharge from underground conduits created by the karst terrain. The creek has an average discharge of 3cfs and according to Hurd et al. (21) it maintains a nearly constant flow year round due to the influence of water flow from losing streams flowing over the colluvial mantle on the north side of South Mountain. Review of the Literature Introduction Karst terrains make up about 12 percent of the global land surface (Mudarra & Andreo, 211). Karst aquifers present hydrological characteristics that distinguish them from other aquifers and are characterized by distributions of various types of porosity such as porosity within the matrix rock, fractures, faults, bedding planes, and conduits (Mudarra & Andreo, 211, Moore et al., 21). The range of porosity and permeability determines flow paths and affect recharge to the aquifer and can vary on seasonal or individual storm time scales (Moore et al., 21). Recharge, in karst aquifers, can either be diffuse (through the vadose zone) or concentrated (conduit flow) and can be derived from outcrops of karst rocks or beyond from sink holes and swallets (Mudarra & Andreo, 211, Moore et al., 21). Springs emanating from karst aquifers are one of the visible signs of the influence of groundwater hydrology on the Earth s surface (Desmarais &Rojstaczer, 22). To distinguish different types of carbonate aquifers, including diffuse and conduit systems, the hydrologic response time between a precipitation event and a springs discharge rate can be analyzed (Mudarra & Andreo, 211). 2

6 Studies using precipitation and spring discharge rates A study done on the Alta Cadena, a carbonate mountain range in southern Spain, used two years of discharge rates and chemical composition data (ph, temperature, and specific conductivity) of three springs to determine the saturated and unsaturated zones within a carbonate aquifer (Mudarra & Andreo, 211). Mudarra and Andreo (211) concluded that the lag or response time to precipitation along with chemical analysis are useful in estimating the degree of karst development and in determining the type of system (i.e. diffuse or conduit). Desmarais and Rojstaczer (22) examined high resolution variations in spring flow, temperature, and chemistry over several months to infer the source of water for a large carbonate spring on the Oak Ridge Reservation, Tennessee. Precipitation from 14 storms and discharge rates from a spring were used to determine that the aquifer has a high loading efficiency. The results showed that a small amount of recharge occurred from the soil zone and that the recession of the spring appeared to be diffuse in nature. Studies using a water budget Ozlar (21) compared precipitation and discharge rates and created a water budget for the karst basin in the Anatolia karst region in Turkey. The results of the study showed that the karst aquifer discharges water through small springs which are characterized by small discharge rates, short residence times, and short, well regulated spring flows and that variation in monthly precipitation does not have an immediate effect on the total discharge. This study illustrates that the flow regimes of some large springs discharging from karst aquifer systems can be analyzed using hydrographs. In a similar study, Valdiya and Bartarya (1991) used 4 years of precipitation and discharge data from numerous springs throughout the Gaula River catchment in India to determine spring discharge lost to development. A water budget was constructed to determine: potential evapotranspiration, actual evaporation, water deficiency, surplus, and runoff. The water budget made it possible to deduce seasonal and geographical patterns of water supply 3

7 and the resulting hydrographs showed that soil water and groundwater were being used at maximum capacity. The results illustrated the relationship between discharge rates and precipitation and were used to determine the amount of water loss to springs due to land use changes within the study area. Methods To answer the question can a relationship between Big Spring Creek s discharge and climate data be used to determined future discharge?, discharge and precipitation data needed to be collected. Big Spring Creeks average daily discharge data, for the years 25-21, was collected from the USGS website at no Daily precipitation data, for 25-21, was collected from Shippensburg University at These data sets were then entered into Excel and a water budget was calculated (see Appendix A). The water budget was initially calculated with a ratio of 5/5, with 5 percent of precipitation being held in storage for future use and 5 percent used immediately for runoff. A statistical analysis was performed on the relationship between discharge and runoff (from the water budget calculations) and between discharge and precipitation, the R squared value was used to find the best fit for the hydrology of Big Spring Creek. Charts and graphs were then generated to show the relationship between the climate data and discharge rates at Big Spring Creek. Results Analysis of water budget The results of the water budget analysis (see Appendix A) show that, from the years 25 through 21, during the summer months there is a deficit (D) in the amount of moisture available. There is an inverse relationship between moisture surplus (S) which is greatest during the fall, winter and spring months (Figure 2). Runoff (RO) follows the path of both surplus and deficits. During periods of high surplus there is more moisture available for runoff and during periods of deficit less water is available due to recharging of the soil and aquifer and loss to 4

8 (mm) (mm) evapotranspiration. Figure 2 shows that for the years 29 and 21 there is more moisture Date D (mm) S (mm) RO (mm) Figure 2: Illustration, from the calculated water budget, of the relationship between water deficit, surplus, and runoff amounts for the years This model assumes that 7% is held in detention and 3% is runoff. Data source: Shippensburg University. available for surplus and little to no deficit in the summer months. The total deficit for the years is 286.1mm with an average 71.5mm per year. In 29, the deficit for the year is 3.5mm and no deficit at all for 21. The total surplus for the six year period is mm with an average of 428.5mm per year available for runoff. Figure 3 illustrates the relationship between precipitation (P), actual (AE), and potential evapotranspiration (PE), calculated from the water budget. Actual and potential Date PE (mm) P (mm) AE (mm) Figure 3: Illustration of the relationship between average monthly precipitation and calculated potential and actual evapotranspiration for Data source: Shippensburg University 5

9 (mm) Discharge (cms) evapotranspiration are highest in the summer months and follow each other relatively close. Precipitation, in the spring and summer months of 25, 26, 29, and 21, exceed the actual and potential evapotranspiration rates and during the summer of 27 and 28 evapotranspiration is higher than recorded precipitation amounts. Comparing surplus, deficit, and precipitation with the average monthly discharge (Q) of Big Spring Creek, some relationship is shown between the amount of surplus moisture and the amount of discharge (Figure 4). When there is an increase in surplus moisture and there is a precipitation event there is a similar increase in the amount of discharge at Big Spring Creek Date S (mm) D (mm) P (mm) Q (cms) Figure 4: Illustration of the relationship between average monthly precipitation, surplus, deficit and discharge rates for the years During the summer months, when evapotranspiration is the highest and moisture deficit is the greatest, there is a similar decline in discharge even though there are high precipitation amounts for some months. One example is July 25, mm of precipitation occurred but no observable increase in discharge is noted possibly because of already elevated discharge rates combined with a deficit in moisture. During the summer, when moisture deficit is the greatest, Big Spring Creek maintains an average flow of 8.5cms suggesting that surplus moisture from previous months sustains it s flow. 6

10 6/1/26 6/5/26 6/9/26 6/13/26 6/17/26 6/21/26 6/25/26 6/29/26 7/3/26 7/7/26 7/11/26 7/15/26 7/19/26 7/23/26 7/27/26 7/31/26 Discharge (cms) Precipitation (mm) 5/1/25 5/8/25 5/15/25 5/22/25 5/29/25 6/5/25 6/12/25 6/19/25 6/26/25 7/3/25 7/1/25 7/17/25 7/24/25 7/31/25 Discharge (cms) Precipitation (mm) When looking at the average daily discharge and precipitation from May 1, 25 to July 31, 25 (Figure 5), it shows that discharge steadily declines with some small responses to precipitation with the exception of July 15 th where no response is noted. This relationship between deficit and lowered discharge can be seen in the summer months of 25, 26, 27, Date Discharge (cms) Precip Figure 5: Illustration of average daily discharge and precipitation at Big Spring Creek for May-July 25 showing increased decline in discharge rates even with large precipitation events. and 28 and on a smaller scale in 29. This decline indicates that when a deficit is present, and there is a high precipitation event, water is either being stored or used for evapotranspiration instead of flowing as runoff to Big Spring Creek. The discharge at Big Spring Creek seems to follow the rates of surplus and deficit moisture with a few exceptions such as the winter of 27 where precipitation and storage are high but discharge shows a decline The amount of precipitation also has an impact on the amount of discharge. High precipitation, during periods of surplus, tends to lead to an increase in the amount of discharge Date Discharge (cms) Precip Figure 6: Hydrograph for June and July 26, illustrating lag time between precipitation and discharge at Big Spring Creek during a period of surplus. after a small lag time (Figure 6). There are some discrepancies between precipitation and discharge: during the spring of 25 there is a large increase in the amount of discharge, but little precipitation. This anomaly is not repeated even though there are years with much higher rainfall totals. The spring of 21, there is a similar smaller 7

11 Discharge (cms) Discharge (cms) Discharge (cms) /3 y =.23x R² = Runoff (mm) 1.4 8/ /4 y =.17x R² = Runoff (mm) y =.28x R² = Runoff (mm) Figure 7: illustration of the relationship between Big Spring Creeks average monthly discharge rates and various calculations for runoff and surplus amounts from the water budget for increase in the amount of discharge with no major precipitation amount. This may indicate that there were large snowmelt events in the spring months which increased runoff rates with no precipitation being recorded. The water budget was initially calculated with a ratio of 5/5, with 5 percent of precipitation being held in storage for future use and 5 percent used immediately for runoff. The calculations for storage and runoff were then manipulated to find the best fit for the hydrology of Big Spring Creek. In order to compare the average monthly discharge and the calculated runoff from the water budget, scatterplots were created and the R squared value was used to determine the strength of the relationship between discharge and runoff. Figure 7 indicates that the strongest relationship between discharge and runoff occurs with a ratio of 7/3 with 7 percent of precipitation held in storage and 3 percent available for runoff. This ratio has the highest R squared value of When the water budget ratio, was adjusted to 6/4 (6% held in storage, 4% available for runoff) the R squared value decreased to.17 and when the ratio was adjusted to 8/2 the R squared value decreased to.1147 between discharge and runoff.

12 Q (cms) Runoff (mm) Q (cms) Runoff (mm) Q (cms) Runoff (mm) / The R squared value for the 7/3 scenario may be the best fit, but it still depicts that there is little relationship between runoff and discharge rates at Big Date Q (cms) RO (mm) 1.4 7/ Spring Creek. Several charts were made to compare the average monthly discharge rates and calculated runoff for 25 through 21 using all combinations for the distribution Date 8/2 Date Q (cms) Q (cms) RO (mm) Figure 8: Illustration of the relationship between runoff and discharge rates for the years Models based on the various calculations from the water budget for detention and runoff ratios.. RO (mm) between moisture surplus and runoff. The charts in Figure 8 show the different adjusted ratios between each of the scenarios used in Figure 7 s scatterplots, where the R squared value determined that a 7/3 ratio was the best fit for Big Spring Creek. There are subtle differences between all the scenarios: the more moisture that is held in detention (such as the 8/2 chart) and less devoted to runoff skews the chart in one direction and when less moisture is held in detention and more is available for runoff (such as the 6/4 chart) the runoff exceeds the discharge. All the charts show that there is some relationship between runoff amounts and discharge at Big Spring Creek, when a lag time is taken into consideration. These charts depict that when runoff totals are high, there is a lag time and then a peak in the amount 9

13 Runoff (mm) Discharge (cms) Discharge (cms) of discharge. There are exceptions where high runoff does not coincide with a peak in discharge (such as November 27). When calculated runoff totals are low there is a similar decline in the amount of discharge at Big Spring. There are several instances when discharge and runoff do not coincide. One example is October 25, where there is an increase in discharge but runoff remains low. This may indicate that flow is being sustained and increased from water storage y =.43x R² = Runoff (mm) Figure 9: Relationship between projected calculated runoff (3/25-11/21) and Big Spring Creeks discharge rates (4/25-12/21). To compensate for the lag time between calculated runoff and peaks in discharge rates, a scatterplot was created where runoff was moved forward a month to match future discharge rates (Figure 9). By projecting runoff to a month in the future, the R squared value is increased from.1281(figure 7) to.4774 (both R squared values use the 7/3 ratio) showing that there is more of a relationship between discharge and runoff when runoff is projected into the future. This can be Date RO (mm) Q (cms) Figure 1: Relationship between calculated runoff and discharge. When runoff is projected one month into the future and matched to Big Springs discharge rates. seen in Figure 1, where calculated runoff amounts coincide and, in some areas, exceed peaks in discharge. The water budget calculation does not consider the size of the drainage basin nor does it differentiate between rapid surface flow and slower moving groundwater flow. Figure 1 illustrates that Big Spring Creek s discharge shows more of a response to runoff when the runoff 1

14 1/1/25 4/1/25 7/1/25 1/1/25 1/1/26 4/1/26 7/1/26 1/1/26 1/1/27 4/1/27 7/1/27 1/1/27 1/1/28 4/1/28 7/1/28 1/1/28 1/1/29 4/1/29 7/1/29 1/1/29 1/1/21 4/1/21 7/1/21 1/1/21 Discahrge (cfs) Discharge (cfs) is projected into the future month s discharge. This may indicate that Big Spring s discharge is dominated by a more diffuse flow from moisture that is held in storage and is being slowly released or that recharge is occurring from slower moving groundwater. By adjusting the water budget calculations, to 7 percent water moisture held in storage and to 3 percent of water available to runoff a more accurate depiction between discharge and runoff was able to be made. When runoff was projected a month into the future and compared with Big Springs discharge the relationship with runoff was visibly increased. Analysis of daily precipitation and discharge To show the results between average daily precipitation and average daily discharge, for 25 to 21, a scatterplot was created (Figure 11). The results of the scatterplot show that when daily precipitation and discharge are compared there is little statistical y =.3143x R² = Figure 11: Scatterplot showing the relationship between daily discharge and precipitation for relationship between the two. This relationship or lack thereof, can be seen in Figure 12 where there are a few precipitation events that directly coincide with increased discharge rates such as Figure 12: Comparison between daily discharge and precipitation for Date Discharge (cfs) Precip 11

15 6/22/26 6/23/26 6/24/26 6/25/26 6/26/26 6/27/26 6/28/26 6/29/26 Discharge (cfs) Discharge (cfs) June 27, 26 when over two and a half inches of rainfall occurred and on June 28, 26 discharge increased to over 5cfs (average discharge is 3cfs). This shows that with large rainfall events there is a short lag time (1 day) then a peak in discharge. When the chart is viewed as a whole, there is little correlation between precipitation and discharge at Big Spring Creek. Scatterplots and graphs were used to compare, on a daily basis, two separate large rainfall events. One of the events took place from June 22, 26 to June 29, 26 where y = x R² = inches of rainfall occurred over the seven day time period. The other took place from September 26, 21 to October 2, 21 where 5.34 inches of rainfall occurred over a six day time period. The scatterplot for the 26 rainfall shows little relationship between the event and discharge rates at Big Spring Creek (Figure 13). Increases in discharge correlate more to decreased precipitation Day Q(cfs) Precip Figure 13: Relationship between daily precipitation and discharge during a seven day precipitation event for June 22, 26 June 29, 26. as shown by the trend line. When viewing the graph of precipitation versus the discharge at Big Spring Creek, decreased precipitation relates to little response in discharge. As the amount of precipitation increases, there is a lag time of a day and the discharge rate begins to climb and at the height of the event, discharge peaks then starts declining. This relationship is indicative that storm water flow is causing the immediate rise in discharge but doesn t affect the long term average discharge rates at Big Spring Creek. The 12

16 9/26/21 9/27/21 9/28/21 9/29/21 9/3/21 1/1/21 Discharge (cfs) Discharge (cfs) scatterplot for the 21 rainfall event shows that with an increase in precipitation there is a slight increase in the amount of discharge. The slight increase in discharge is correlated to a high precipitation event and can be seen by looking at the trend line. When viewing the graph of precipitation versus discharge rates at Big Spring Creek, it resembles the graph in Figure 13 where discharge remains fairly stagnant even though there is about an inch and a half of y =.493x R² = Day Q(cfs) Precip Figure 14: Relationship between daily precipitation and discharge during a six day precipitation event for August 26, 21 September 2, 21. rainfall. As the rain event continues for a longer period of time, Big Spring s Discharge begins to respond with a slight increase and after a major rainfall on the 3 th the discharge peaks on the 1 st. This relationship between precipitation and Big Spring s discharge shows some response to storm water runoff, but only for a short duration. This relationship indicates that the main source of water to Big Spring comes from another source other than storm water. There is a difference between the two rainfall fall events: the June, 26 event occurred during a period of surplus according to the monthly water budget and discharge rates at Big Spring reached the 5cfs mark; the September, 21 precipitation event occurred during a period of deficit and the peak in discharge reached only 31cfs, indicating that storage and deficits in moisture have an effect on the amount of discharge that Big Spring produces over a long period of time. A comparison was made between weekly averages of precipitation and discharge rates (for each year) the results are shown in Figure 15. Some comparisons and correlations can be 13

17 1/3/9 2/3/9 3/3/9 4/3/9 5/3/9 6/3/9 7/3/9 8/3/9 9/3/9 1/3/9 11/3/9 12/3/9 1/2/1 2/2/1 3/2/1 4/2/1 5/2/1 6/2/1 7/2/1 8/2/1 9/2/1 1/2/1 11/2/1 12/2/1 1/6/7 2/6/7 3/6/7 4/6/7 5/6/7 6/6/7 7/6/7 8/6/7 9/6/7 1/6/7 11/6/7 12/6/7 1/5/8 2/5/8 3/5/8 4/5/8 5/5/8 6/5/8 7/5/8 8/5/8 9/5/8 1/5/8 11/5/8 12/5/8 Discharge (cfs) 1/1/5 2/1/5 3/1/5 4/1/5 5/1/5 6/1/5 7/1/5 8/1/5 9/1/5 1/1/5 11/1/5 12/1/5 1/7/6 2/7/6 3/7/6 4/7/6 5/7/6 6/7/6 7/7/6 8/7/6 9/7/6 1/7/6 11/7/6 12/7/6 made such as the week of July 1, 26 where precipitation has a decided peak along with discharge rates. When the year, as a whole, is viewed there are more discrepancies between Q (cfs) Precip total 1 Figure 15: Illustration of average weekly precipitation totals and average weekly discharge rates for the years discharge and precipitation. This is fairly clear when viewing the weekly averages for 21, there is very little indication of a response from the spring to precipitation throughout this year. There are some small peaks in relation to precipitation but, discharge continues to decline throughout the year. An example is August 1 th to September 2 nd, 21 where over 5 inches of 14

18 Spring 5 Summer 5 Fall 5 Winter 6 Spring 6 Summer 6 Fall 6 Winter 7 Spring 7 Summer 7 Fall 7 Winter 8 Spring 8 Summer 8 Fall 8 Winter 9 Spring 9 Summer 9 Fall 9 Winter 1 Spring 1 Summer 1 Fall 1 Discharge (cfs) precipitation is recorded but there is no peak in the discharge rate. This response is probably related to a seasonal deficit in the water budget for the year. Increased discharge in the spring of 21 may indicate a lag time from precipitation being held in storage, from the 29 year, and then released in the spring of 21 possibly as snowmelt. Average daily discharge and total daily precipitation were compared on a seasonal basis. To show the comparison, the average discharge and the total precipitation were calculated for each season (Spring (MAM), Summer (JJA), Fall (SON), and Winter (DJF)). To make the comparison even, January and February of 25 and Season & Year Q(cfs) Precip Figure 16: Illustration of the total precipitation and average discharge calculated seasonally for The seasonal rates do not include Jan 25, Feb 25, and Dec 21. December of 21 were left out since they did not contain data for the full season. A graph was then generated to show the seasonal relationship between discharge and precipitation (Figure 16). The graph indicates that precipitation and discharge, when compared seasonally, follow each other well. When there is a peak in precipitation there is a similar peak in discharge and when precipitation totals drop there is a similar drop in the discharge rates of Big Spring Creek. The statistical relationship for this comparison was very low and any efforts to improve it by projecting precipitation to a future discharge rate did not work. This may mean that the seasonal representation, in the graph, is the best scenario for Big Spring Creek. Looking at the six month average discharge and the six month total precipitation for the time periods, there seems to be no correlation between precipitation and discharge. Figure 17 illustrates an almost inverse relationship with discharge throughout the study period. 15

19 Discaharge (cfs) 1-Jan-5 1-Jul-5 1-Jan-6 1-Jul-6 1-Jan-7 1-Jul-7 1-Jan-8 1-Jul-8 1-Jan-9 1-Jul-9 1-Jan-1 1-Jul-1 Discharge (cfs) The only relationship is found on January 1, 28 where the six month total precipitation and the six month average discharge exhibit the same peak on the graph. For the rest of the time period, the six month average discharge and precipitation are shown as having an inverse Date Q (cfs) Precip Figure 17: Illustration of the six month average in discharge and the six month total precipitation for relationship. In order to determine the strength of the relationship between Big Spring s discharge and precipitation, a scatterplot was made (Figure 18). The results of the scatterplot show that there is very little relationship between the six month averages between discharge and precipitation (according to the R squared value). To increase the relationship between the y = x R² = six month total precipitation and the six month average discharge, precipitation was projected six months into the future (precipitation Jan 25-Jan 21 projected to June 25-June 21) and compared to Big Spring Creek s six month average discharge. The scatterplot in Figure 18: Illustration of the six month total precipitation and average discharge for showing the strength of the relationship between them. Figure 19 shows, that by projecting precipitation to future discharge rates, the R squared value was increased from.166 (Figure 19) to.422 increasing the relationship between precipitation and discharge. This 16

20 Discharge (cfs) 1-Jun-5 1-Dec-5 1-Jun-6 1-Dec-6 1-Jun-7 1-Dec-7 1-Jun-8 1-Dec-8 1-Jun-9 1-Dec-9 1-Jun-1 Discharge (cfs) Discahrge (cfs) y =.5147x R² = Figure 19: The average six month discharge and the six month total precipitation for Precipitation was projected six months into the future and the relationship between precipitation and discharge shown. relationship can be seen in the graph (Figure 2) and shows that precipitation and discharge follow each fairly well with one exception, June 1, 28. On June 1 st, there is an increase in precipitation but, a decrease in discharge is shown. The relationship between the average six month discharge rate and the six month total precipitation indicate that very little precipitation is effectively transferred to the Date Q(cfs) Precip Figure 2: The average six month discharge and the six month total precipitation for Precipitation was projected six months into the future. spring during rainfall events and that it is held in storage and slowly released to the system at a point in the future similar to the lag time seen with runoff only on a longer time scale Year Q (cfs) Precip Figure 21: Illustration of total yearly precipitation and average yearly discharge rates for A final comparison was made for the total yearly precipitation amounts and the average yearly discharge for Big Spring Creek. Figure 21 illustrates that comparing yearly rates is not very helpful in

21 determining future discharge. This method might prove useful if there were a hundred years worth of data to compare and even then it would not provide an accurate assessment of climate/discharge relationships on a day to day or month to month basis. Discussion The method that proved most useful was the constructing of a water budget. The results of the comparison between discharge and the calculated water budget provided useful information about the trends in flow experienced by Big Spring throughout the seasons. It was shown that during the summer when evapotranspiration is high and a water deficit occurs, the overall flow of Big Spring diminishes even though a high precipitation event might occur. During periods of water surplus, high precipitation events are documented with peaks in the discharge of Big Spring. The surplus/runoff ratio was adjusted to 7/3 by using the R squared value as an indicator of the relationship between the different models. By adjusting the ratio, discharge rates were more easily matched with runoff and by projecting runoff to future discharge rates the statistical relationship was increased and a better model was made. The water budget calculation, for runoff, does not consider the size of the drainage basin nor does it differentiate between rapid surface flow and slower moving groundwater flow. The results from this analysis show that Big Spring is dominated by more diffuse flow from runoff that is slower moving instead of faster moving overland flow. Peaks in discharge, during periods of high water surplus, indicate that when the soil is saturated and evapotranspiration is low, the flow of water is increased and relates to a response in Big Spring s discharge. The total daily precipitation and the average daily discharge rate showed that the statistical relationship was almost nonexistent but, it proved useful in determining the amount of lag time between an event and the increase in discharge. Using the total daily precipitation and the average daily discharge, two major storm events were compared and illustrated that discharge was not dependent on precipitation, but that when a long term precipitation event 18

22 occurred it generated a response in Big Spring s discharge for a short duration. This information helped determine that storm water flow created the small peaks in discharge after a precipitation event but, that the main influence of flow to Big Spring comes from slower moving groundwater sources. When comparing average weekly discharge with the total weekly precipitation there were very few relationships noted between discharge and precipitation. A seasonal comparison was then made to show the total seasonal precipitation and the average seasonal discharge. This comparison shows that when discharge and precipitation are viewed on a seasonal basis, high precipitation coincides with increased discharge and little precipitation coincides with lower discharge and that Big Spring follows seasonal variation fairly well although the statistical relationship was not that good. A comparison was made between the six month total precipitation and the six month average discharge. The initial results of the comparison showed an inverse relationship between precipitation and discharge. To increase the relationship, precipitation was projected six months into the future and matched with discharge. By projecting precipitation, the statistical relationship was increased and the results showed a close correlation between precipitation and discharge. Indicating that Big Spring receives flow not just from immediate storm water events but from precipitation that has percolated through the soil and is slowly being released back into the system on a longer time scale. Finally, when comparing the yearly average discharge and the total yearly precipitation there was very little relationship shown between the two. This method proved not to be helpful for determining a relationship between discharge and precipitation. In order for this method to provide insight into the yearly patterns of discharge and precipitation more data would be required to make a long term association and would still not provide insight into the daily or monthly variations between precipitation and discharge. 19

23 Conclusion Information from weather data can be used to make predictions about future discharge rates for Big Spring Creek. Observing climatic conditions such as trends in surplus, deficit, evapotranspiration rates, runoff (calculated from a water budget) and precipitation provide insight into the conditions present at the time of increased or decreased discharge at Big Spring Creek. By observing these past climate conditions and Big Spring s responses to these conditions, predictions about discharge can be made from the observations of climate patterns. Appendix A Table 1: Big Spring Creek Monthly water budget for the years Date T(C) P (mm) PE (mm) P-PE (mm) SM (mm) DSM (mm) S (mm) AE (mm) D (mm) S avail (mm) RO (mm) Beta Q (cms)

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25 Works Cited Becher, A., Root, S Groundwater and Geology of the Cumberland Valley, Cumberland County, Pennsylvania. Pennsylvania Geological Survey. 4 th ser. Water Resource Report 5.p.95. Chichester, D.D Hydrogeology of and simulation of ground-water flow in a mantled carbonate-rock system, Cumberland County, Pennsylvania. U.S. Geological Survey Water-Resources Investigation Report p39. Desmarais, K., Rojstaczar, S. 22.Inferring source waters from measurements of carbonate spring response to storms. Journal of Hydrology. 26: Hurd, T.M., Brookhart-Rebert, A., Feeney, T.P., Otz, M.H., Otz, I. 21. Fast, regional conduit flow to an exceptional-value spring-fed creek: Implications for source-water protection in mantled karst of South-Central Pennsylvania. Journal of Caves and Karst Studies. 73(3): Lindsey, B.D. 25. Hydrogeology and Simulation of Source Areas of Water to Production Wells in a Culluvium-mantled Carbonate Bedrock Aquifer Near Shippensburg, Cumberland and Franklin Counties, Pennsylvania. U.S. Geological Survey. Scientific Investigation Report p Moore, P.J., Martin, J.B. Screaton, E.J. 21. Geochemical and statistical evidence of recharge mixing and controls on spring discharge in an exogenetic karst aquifer. Journal of Hydrology. 376: Mudarra, M., Andreo, B Relative importance of the saturated and unsaturated zones in the hydrogeological functioning of karst aquifers: The case of Alta Cadena (Southern Spain). Journal of Hydrology. 397: Ozler, M.H. 21. Karst hydrogeology of Kusluk-Dilmetas karst spring, Van Eastern Turkey. Environmental Geology. 41: United States Geologic Survey (USGS). 29. National Water Information System. Department of the Interior. U.S. Geological Survey. Accessed January 19, 212. Valdiya, K.S., Bartarya, S.K Hydrogeologic Studies of Springs in the Catchment of the Gaula River, Kumaun Lesser Himalaya, India. Mountain Research and Development. 11(3): Van Diver, B.B Roadside Geology of Pennsylvania. Mountain Press Publishing Company. QE157. V