Wetland River Flow Interaction

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Wetland river flow interaction in the white Volta basin, Ghana
Abstraction
Groundwater in the White Volta River basin plays a critical function in the economic system of Ghana by moving as a major beginning of H2O for agribusiness activities for communities populating about. During three old ages of survey, 12 observation Wellss were monitored ; groundwater informations were obtained from two distinguishable geological formations. Groundwater information obtained in concurrence with stratigraphy/topography groundwater conditions were qualify within the landscape. Groundwater status indicates a systematic fluctuation in response to alterations geological formation and rainfall form with March, April, and May demoing a high degree of draw down. Areas along the chief watercourse indicated a high H2O degree with the hydraulic gradient towards the upper catchment. Nevertheless, a bidirectional flow was observed, throughout each rainfall twelvemonth.
Introduction
Floodplains wetlands are formed on strips of land surrounding a chief class of a river, it get inundated during seasonal inundations ( Bridge 2005 ) . Floodplains and its associated wetlands may widen from few to several metres along the river strip. Wetland provides a batch of environmental benefits such as home ground for wildlife, H2O purification, groundwater recharge and production of biomass. In some state of affairs subsurface and surface H2O in wetlands sites are pumped for irrigation activities in the dry season ( ……………… ) . In most developing states non much probe has been done in any of the river basins to catalog or make a database on the distribution and types of wetlands ; though it appears to be on diminution due to the destructive nature of human activities and clime alteration ( — — — — — — ) . Wetland found within river basins have of import ecosystem, but direction patterns are non available, because of deficiency of sufficient scientific information to back up any meaningful determination devising by establishment involve in environment and H2O resources direction. To cover with jobs related to flood plains such as inundations, H2O supply, flood plain irrigation, river bank eroding, and redress of contaminated surface H2O and groundwater, earth scientist and civil, agricultural applied scientists must understand rivers and flood plains ( Bridge 2005 ) .
Wetlands have a spacial and temporal complex hydrological system as a consequence of interaction it has with it environing ( Mansel et al. , 2000 ) . The complexness of subsurface and surface H2O inteaction processes in wetland sites does non happen in any terrain but are frequently governed by localised groundwater flow ; these flows are frequently governed by the regional flow procedure influenced by nature of the landscapes ( Fares et al. , 1997 ) . In the Volta River basin recharge to subsurface H2O is cut downing taking to low degree of hydraulic caputs in the aquifers ( Nicola, 2005 ) . The hydrology of wetlands in the basin is complex because some sites are characterized by temporally variable volumes and surface countries of free H2O. This survey is an effort to look into the interaction between wetland and river flow utilizing a two dimensional theoretical account –MODFLOW.
Theoretical background
Groundwater and surface H2O system in flood plain environment are non stray constituents of the hydrological rhythm, but alternatively interact in a assortment of physiographic and climatic landscapes. Understanding the basic rules of patterning interaction between groundwater and surface H2O is indispensable for efficient and effectual H2O resources direction. Modeling wetland hydrokineticss needs to give cardinal consideration to the natural philosophies of surface flow processes ( Grapes et al. , 2005 ) . Water flow in wetlands can be represented by an overall H2O motion frequently dominated slough channel flow, i.e. , flow through a web of unfastened H2O channels that exist between countries or spots of heavy flora ( Lewandowski 1993 ) .
Groundwater modeling is a many-sided undertaking by which greater apprehension of the physical, chemical and biological status in the subsurface can be achieved. Groundwater and surface H2O interaction theoretical accounts are analytical tools for word picture and anticipation of the measure and quality of groundwater. In trying to understand land H2O and surface H2O interaction most research has been on the perpendicular interaction of surface and groundwater. For case, Nield et Al. ( 1994 ) used a numerical theoretical account to analyze groundwater flow in perpendicular subdivisions near surface H2O organic structures, such as lakes, wetlands, pools, rivers, canals, and drainage and irrigation channels. They distinguished different flow governments by observing the presence and nature of groundwater hills or depressions near the borders of a surface H2O organic structure and by matching stagnancy points. Matos et Al. ( 2002 ) examined aquifer heterogeneousness and channel form on flow interactions between watercourse and groundwater systems. In such a survey, MODFLOW, was used, to measure the magnitude, way and spacial distribution of stream-subsurface exchange flows, with the underlying deposits moving as an aquifer. Harmonizing to Richardson et Al. ( 2001 ) , exchange between groundwater and surface H2O infiltrating H2O moves along a gradient making an hindering beds of clay The infiltrating H2O moves along the hydraulic gradient until it reaches an hindering bed of all right clay and silt, which has a lower hydraulic conduction ; therefore less H2O is transmitted per unit clip. FLOWNET, FEFLOW, MIKE-SHE and other numerical theoretical accounts have been used to plot and visualise equal hydraulic caputs and groundwater flow waies and largely consist of equipotential lines and flow watercourse lines. Physical-based, process-oriented and spatially distributed theoretical accounts have rarely been applied to analyze wetlands in developing states, since they are complex to run and necessitate a degree of informations that is barely available in most underdeveloped states because of cost ( Bonell and Balek 1993 ) .
Modeling of flood plain wetland and river interaction is both numerically and theoretically demanding and requires work outing complicated numerical estimates to differential equations ( Bockelmann et al. 2004 ; Fischer-Antze et Al. 2001 ; Wu et Al. 2000 ) .
In most instances wetlands are by and large incorporated in groundwater theoretical accounts as general caput boundary nodes even though they can be used as changeless caputs ( Restropo et al. 1998 ) . The hydrologic government of flood plain wetlands depends on the changing grade of flow in the chief channel, doing wetlands vulnerable to hydrologic alterations ensuing from flow ordinance ( Reid and Quinn 2004 ; Cloke at Al. 2006 ) . However, the nonlinear interactions among recharge, discharge, boundary conditions and alterations in groundwater storage makes the resolution of jobs associating to reload and groundwater development hard, all the system parametric quantities and their geographical distribution are non carefully accounted for ( Sanford 2002 ) .
Notably rivers interact with the flood plain wetland in three ways: 1 ) through direct surface overflow, 2 ) through sub-surface H2O flow, and 3 ) by losing H2O to wetlands by ooze through the river walls. The interaction between flood plain wetlands and a river sometimes vary, over a really short clip frame or distance in response to rapid rises in river phase due to ramp overflow. For case the high H2O degree in the White Volta River as in 1994 and 2007 was plenty to overrun the Bankss and flood big countries of the flood plains doing a widespread surface recharge. Therefore, the hydraulic connexion between the White Volta River and the flood plain wetland may be direct or disconnected by the intervening unsaturated zone, with rivers losing H2O in the signifier of ooze through the walls into the flood plain wetland. Important in flood plain wetland hydrological mold within the Upper East part is to set up the part of shallow well development for the nutriment of dry season irrigation. This paper discusses procedures involved in the usage of PM-WIN ( MODFLOW ) , to find signifiers of interaction between the chief White Volta River and the basin flood plain wetlands. The survey is sectioned into three chief parts: 1 ) an overview of the theoretical account ; 2 ) treatment of the scene of the MODFLOW theoretical account, bespeaking the input informations used ; 3 ) treatment of theoretical account consequences and sensitiveness analysis.
PM-WIN ( MODFLOW ) can imitate many of the characteristics act uponing the in-field H2O government, including anisotropy and heterogeneousness in hydraulic belongingss. In patterning flood plain wetland river flow interaction at the Pwalugu site was performed utilizing PM-WIN ( MODFLOW ) was used ( Chaing and Kinzelbach 1998 ) for the undermentioned grounds:

MODFLOW takes history of spacial heterogeneousnesss, perpendicular groundwater flow and any regional groundwater flow constituent.
Escapes through heavy dirts can happen at low rates and accordingly go a minor constituent at the field graduated table, although the volume of escape can be important over the entire country of the wetland.
Irregular field boundaries and steep hydraulic gradients to the river are accommodated.
Recharge can be distributed spatially, and recharge is assumed to be added outright to the saturated zone.
MODFLOW allows vaporization from the dirt surface, therefore the maximal vaporization rate is assigned to each cell when the H2O tabular array peers an assigned caput value and ceases below the assigned extinction deepness.
The PMWIN theoretical account is free.

Model Description
The Pwalugu flood plain wetland site is represented by an array of rectangular cells, which embody the localised values of the aquifer features ( Figure 1.1 ) . The country modeled screens 7.78 km2 and comprises 8648 square cells, out of which 5693 are marked as active cells. The theoretical account for the survey site is represented in two beds, and the top of the topmost bed ( Figure 1.2 ) corresponds to the surface of the flood plain wetland ; this bed can be dried and rewetted seasonally. The thickness of the top bed varies in thickness from 6.0 m when stopping point to river and 26 m at the eastern lodger of the survey site. The 2nd bed below has a thickness of 10 m, specified on the footing of a geological formation that limits storage and enhances transmittal of H2O. The spacial bounds of the geological formations provided no-flow boundaries to the North and west side of the river ( Figure 1.1 ) . Flow along the southern and eastern boundaries is specified as changeless caput. The theoretical account is specified to enable finding of whether the wetlands contribute to or receive H2O from the river. This depends on the caput gradient between the flood plain wetland and the river. The bundles river, recharge and wetting capablenesss were applied during the mold procedure.
[ image ]
Figure 1.1 Setting of the Pwalugu flood plain wetland site
[ image ]
Figure 1.2 Location and transect of wetlands in the White Volta River basin
The river bundle ( Prudic 1989 ) was used to stand for the White Volta River in the theoretical account. The White Volta River can derive from or lend H2O to the flood plain wetland depending on the river phase ( Figure 1.3 ) , riverbed conductance and next flood plain aquifer H2O degrees. The river surface lift informations are measured by the Hydrological Service of Ghana. The low degree of 133.05 m was recorded in January 2005, while September 2005 had the highest reading of 140.53 m.
[ image ]
Figure 1.3 River gage highs at Pwalugu Station
Riverbed conductance is a critical parametric quantity in finding the sum of H2O ooze between the river and implicit in aquifer ( Hayashi and Rosenberry 2002 ) . Conductance values of between 3.09 x 104m/day and 3.10 tens 104m/day were assigned utilizing the hydraulic conductions of the ascertained changing bed stuffs dwelling of alluvial sedimentations, metamorphosed sedimentary and granites outcrops that largely from the river bottom. Data riverbed thickness and river breadths were non available to warrant accommodation of riverbed conductance on a river-segment footing during the mold procedure. To imitate the sidelong flow interaction between wetland and river through the deposit sedimentations, low permeableness values was assigned to the river bed to forestall escape from the river bottom into the implicit in aquifer.
A
Bacillus
C
[ image ] [ image ] [ image ]
Figure 1.4 ( A ) Field study of the White Volta River ( Pwalugu ) ( B ) Cross subdivision at Pwalugu estimating station ( C ) cross subdivision at 150 m upriver from Pwalugu estimating station
The perpendicular and horizontal hydraulic conduction with the flood plain wetlands are non unvarying, but exhibit variableness in footings of deepness and way. Two hydraulic conduction beds were specified. For the top bed, due to spacial heterogeneousness of perpendicular hydraulic conduction, a scope of 0.012 to 0.038 m/day was specified. A scope of 0.12 m/day to 0.38 m/day was specified as the horizontal conduction of the top bed. For the bottom bed, an arbitrary value of 0.09 m/day was specified for both perpendicular and horizontal hydraulic conductions because of deficiency of information about the bed.
Recharge is limited to the behaviour of the geological system that underlies the Pwalugu flood plain wetland site. This serves as a partitioning force that controls sub-surface recharge or H2O motion ( Sanford 2002 ; Fox et Al. 1998 ) . The boundary status in the MODFLOW groundwater theoretical account is efficaciously represented by stipulating net underside flux of HYDRUS-1D as a recharge flux ( figure 1.5 ) . However, in the White Volta basin it is hard to independently obtain an accurate recharge rate and distribution informations. To gauge recharge for the Bongo granite aquifer in the Volta basin, Martin ( 2005 ) used the chloride mass balance, soil wet balance and H2O table fluctuation methods. Martin ( 2005 ) obtained three different recharge values of 5.9 % , 12.5 % and 13 % of the one-year rainfall severally. Apparently, recharge measurings in the field contain some sum of uncertainness ; for the MODFLOW simulation, the bottom flux from the HYDRUS-1D theoretical account was specified as the net recharge ( Figure 1.5 ) for the Pwalugu flood plain wetland. An estimated recharge of 444 millimeter for 16 months ( 487 yearss ) obtained from HYDRUS-1D simulation served as an input into the theoretical account. It is of import to emphasize here that the HYDRUS-1D underside flux as the net recharge into the subsurface ; in this instance, H2O ponding and evapotranspiration has been accounted for.
Groundwater recharge ( millimeter )
[ image ]
Figure 1.5 Monthly underside fluxes from HYDRUS-1D
Floodplain wetland and river flow interaction patterning
The PM-WIN theoretical account assisted to build a planar transient theoretical account to quantify the temporal and spacial fluctuation in the interaction between flood plain wetland and the White Volta River. The simulation of flood plain wetland and river flow interaction is of import in gauging the flow and exchange of H2O between the wetland and river. An premise made during the mold procedure is that, conduction of the river bottom is really low, therefore any signifier of escape from the river is a escape into the wetland through the sub-surface. The theoretical account was run utilizing both steady and transeunt manner.
To first calibrate theoretical account parametric quantities a steady province flow simulation was performed to obtain a tolerable distribution of initial hydraulic caput. The perpendicular and horizontal hydraulic conduction values of the top bed were adjusted to acquire good tantrum for conductions of the beds. For the bottom bed, no value was set for both perpendicular and horizontal hydraulic conduction, because the hydro-geological information was non available ( Table 1.1 ) . In add-on, effectual porousness, specific storage, storage coefficient and specific output of the sub-surface were adjusted to suit the degree of fluctuation happening within the flood plain wetland. The accommodation of the conductions and other parametric quantities shifted the mistake of disagreement between observed and modeled values to an appreciable degree.
Surveies have shown that in trying to understand and to mensurate any hydrological procedure in an environmental scene, there are many different parametric quantity sets within a chosen theoretical account construction that may be acceptable in reproducing the behavior of that system ( Feyen et al. 2004 ; Restrepo et Al. 1998 ) . There is rarely an optimal” theoretical account that can bring forth fake consequences at an acceptable bound of truth, instead it is more of import to see multiple possibilities for imitating in an acceptable scope ( Beven 2001 ; Beven 2009 ) . To imitate consequences within an acceptable scope, there should be sufficient interactions among constituents of a system, unless the elaborate features of these constituents can be isolated and calibrated independently, many representations may be every bit acceptable. Therefore, seeking for optimum parametric quantity representation may non be possible, because it is statistically likely that the description of the system may be incorrect. One justification for utilizing multiple parametric quantity sets to imitate a hydrological procedure that is non-linear roots from the fact that there are uncertainnesss associated with the usage of theoretical accounts in anticipation, because there are many acceptable theoretical account constructions or acceptable parametric quantity sets scattered throughout the parametric quantity infinite ( Beven 2009 ) . Diekkruger ( 2003 ) argued that nonlinear systems are peculiarly sensitive to their initial and boundary status ; therefore any signifier of kineticss in these conditions may be of import in commanding the ascertained response. It suggests that anticipations of all acceptable theoretical accounts should include an appraisal of anticipation uncertainness. Uncertainty in hydrological theoretical accounts stem from the fact that they are non the true contemplation of the procedures involved, because status and information for running the theoretical accounts are non error free. Hence, there is a demand to happen optimal parametric quantities that are efficient and sensitive parametric quantities to pattern ( Beven, 2009 ; Hill 1989 ) . Sensitivity analysis is carried out when initial parameterization is complete.
Sensitivity analysis was performed to quantify comparative alterations in theoretical account end product in response to alterations in input parametric quantity values. This procedure was carried out after theoretical account had been specified, and its benefits include: 1 ) a cheque on the theoretical account logic and hardiness of the simulation, 2 ) designation of the importance of specific theoretical account parametric quantities and matching attempt that must be invested in informations acquisition for different parametric quantities. Dimensionless and dimension scaled are the two chief types of sensitiveness analysis performed in MODFLOWP. These types of sensitiveness analysis mentioned supra have been discussed in item in the plants of Hill ( 1998 ) .
As noted the chief beginnings of uncertainness in patterning Pwalugu flood plain wetland site are the spacial distribution of the horizontal hydraulic conduction, perpendicular hydraulic conduction, specific storage and specific output. While admiting the anisotropic nature of the aquifer sedimentations of the sub-surface sedimentation, nevertheless, anisotropy of horizontal hydraulic conduction ( HK_1 ) , specific storage ( SS_4 ) and specific output ( SY_3 ) were assumed at the graduated table of involvement for the aquifer parametric quantities. The deduction is that uncertainness as a consequence of spacial variableness of conduction of the top bed is non accounted for in the present survey. Van Leeuwen et Al. ( 1999 ) showed that variableness in perpendicular conductance of a confining clay bed strongly affects flow and form of the gaining control zone. In the present survey, variableness is partially accounted for by the spacial fluctuation of the thickness of the top bed.
Sensitivity analysis of horizontal hydraulic conduction ( HK_1 ) , perpendicular hydraulic conduction ( VK_10 ) , specific storage ( SS_4 ) and specific output ( SY_3 ) determined which of the parametric quantities had greatest consequence on the fake caputs. MODFLOWP was used to bring forth sensitivenesss by unhinging the control parametric quantities, during the simulation for 487 yearss on a day-to-day clip stairss footing. The figure of tallies was 19 utilizing 96 observations. Out of the 96 observations 30 had a residuary greater or equal to zero, while the staying 66 had remainders less than zero.
[ image ]
Figure 1.6 Composite graduated table sensitiveness ( horizontal hydraulic conduction ( HK_1 ) , perpendicular hydraulic conduction ( VK_10 ) , specific storage ( SS_4 ) and specific output ( SY_3 )
The composite-scaled sensitiveness ( Figure 1.6 ) indicates the comparative importance of the sub-surface parametric quantities used in the mold processes. During the procedure of theoretical account standardization, HK_1, SS_4 and SY_3 were the parametric quantities with a high degree of sensitiveness, thereby act uponing the interaction procedure between flood plain wetland and White Volta River. VK_10 was insensitive to alterations ; hence it plays no function in the flood plain wetland-White Volta River flow interaction. After optimisation, HK_1 was the most sensitive parametric quantity, and any accommodation of HK_1 increased the sum of interaction between the wetland and the river.
Table 1.1 Adjusted parametric quantities for the PM-WIN theoretical account



Top bed


Bottom bed




Vertical conduction


0.12 – 0.38 /day


0.9 m/day




Horizontal conduction


4 m/day


0.09 m/day




Effective porousness


0.14 – 0.25


0.25




Specific storage


0.01


0.001




Specific output


0.07 m3/day


0.001 m3/day




Storage coefficient


0.01


0.001



In running the steady province theoretical account, the initial hydraulic caput was assumed to be the interpolated hydraulic caput of the piezometers and the river in September 2004. In add-on, no recharge was specified ; nevertheless an equilibrated caput values as initial hydraulic caput for steady and transeunt theoretical accounts. The accommodation proved to be optima for running the theoretical account. The period September to October 2004 was chosen for the standardization, as elaborate hydraulic caput measurings were available for the period.
The transient theoretical account was run in a clip changing manners with day-to-day clip stairss for 487 yearss. The recharge specified was the bottom flux obtained from HYDRUS-1D. Inflow and outflow at the theoretical account boundaries were varied between changeless and variable caput until the theoretical account consequences were in an acceptable scope. The boundary conditions specified do non stand for direct recharge, but are used in concurrence with recharge to realistically stand for the sub-surface H2O system ( Sanford 2002 ) . In running the theoretical account in the transient manner with wetting capablenesss turned on, there was part of H2O flow from cells marked no-flow ( inactive cells ) . In this state of affairs, wetting capableness was removed from the mold procedure. Besides, the bottom bed was disabled due to miss of informations ; hence it becomes a no flow boundary, therefore merely the top bed was used.
Consequences of standardization with the hydraulic conductions and other parametric quantities are shown in figure 1.7 as clip discharge secret plan from six piezometers, for which the deliberate caput follows the form of the ascertained caput. Water degrees in the piezometers are ever elevated in the rainy season and lower in the dry season, but PZ1 at the toe of the inclining portion of the wetland is the last to dry. Datas from piezometers in the Pwalugu flood plain wetland represented subdivisions of the wetlands. The fake curve generated shows a good tantrum with observations particularly for PZ1, PZ2, PZ3, PZ5, PZ8 and PZ9. The rises in the hydraulic caputs of the fake hydrograph are similar and follow a form, while the ascertained hydraulic caput shows some differences. The variableness in the ascertained caputs is likely to be a consequence of heterogeneousness in the sub-surface aquifer construction.
[ image ] [ image ] [ image ] [ image ] [ image ] [ image ]
Figure 1.7 Simulated and observed caputs in the Pwalugu flood plain wetland
The simulation of sub-surface hydraulic caput indicates a systematic fluctuation relation to the White Volta River in response to alterations in the rainfall form in the tropical savanna climatic zone. Over the months of September 2004, December 2004, March 2005, June 2005 and September 2005 ( Figure 1.7 ) distinctive forms of hydraulic caputs were observed. For case, the high hydraulic caput simulated for September 2004 indicates that the flood plain wetland experienced a hydraulic caput between 1 and 3 m below the topographic surface. During August and September, a ponding tallness of 0.50 m was measured in the field. The heterogeneousness of flood plain wetland topography makes ponding uneven. In June 2005, a relatively high hydraulic caput of 4 and 6 m is simulated below the topographic surface but near to the chief river class, while the farther off from the river, the deeper the hydraulic caputs. A bi-direction of sub-surface H2O flow between the White Volta River channel and the flood plain wetland system is inferred as holding a temporal and spacial fluctuation.
September 2004
[ image ]
Figure 1.8 Depth of hydraulic caput and transverse subdivision of flood plain wetland in September 2004, December 2004, March 2005, June 2005, and September 2005
December 2004
[ image ]
Figure 1.8 continued
[ image ] [ image ] [ image ]
Figure 1.8 continued
Figure 1.8 continued
Figure 1.8 continued
Table 1.2 Model fit statistics for the transient run monthly values of ascertained and fake hydraulic caputs



Idaho


Observed ( m )


Simulated ( m )


Root mean square mistake ( RMSE )


Index of Agreement ( IA )




PZ1


136.85


136.79


0.52


0.82




PZ2


137.53


137.00


0.45


0.89




PZ3


137.19


136.87


0.49


0.98




PZ5


136.74


137.04


0.33


0.93




PZ8


136.30


136.04


0.97


0.75




PZ9


135.95


136.47


0.55


0.89



The HYDRUS-1D underside flux used as an input into the theoretical account resulted in a tantrum between the fake hydraulic caput and observed sub-surface H2O degree fluctuation. A comparing of 6 piezometer observations and simulated hydraulic caput showed some outliers with a discrepancy of 1.62 m with a root mean square mistake ( RMSE ) of 1.28 m. Level of compatibility indicates the demand to better theoretical account standardization. Individual piezometers in the wetlands showed differences between the ascertained and fake caput ( Table 1.2 ) . PZ-1 located within the wetland and about 300 m off from the White Volta River gave a better tantrum ( IA = 0.82, MAE = 0.72 m and RMSE = 0.52 m ) . PZ-8 in close propinquity to the river shows a lower IA of 0.75, and RMSE of 0.97 m. Given the deficiency of spacial informations, e.g. , local flow form and hydraulic belongingss with deepness, accurate standardization will non be executable. Therefore, elaborate informations on fluctuation in the landscape, sub-surface H2O degree fluctuation and bottom discharge is required to develop a validated theoretical account of an truth required for direction of flood plain wetlands in the White Volta basin.
The mass balance ( table1.3 ) accounted for the beginnings of H2O for recharge or discharge of a hydrologic system on monthly footing. The cumulative mass balance at the terminal of the run period of 16 months ( 487 yearss ) for the transient theoretical account show the importance of recharge as a H2O balance input. The monthly recharge generated suggests a important part of H2O from wetlands into the river. At sites that do non hold any signifier of sub-surface influence, the signifier of interaction between the wetland and the White Volta River resulted from overbank flow. Another of import procedure is backwater consequence, which contributes to extensive ponding taking to come up H2O storage as noted in the Tindama flood plain wetland.
The interaction conditions vary from season to season, with March, April and May demoing the lowest escape of 0.03 mm/day, 0.06 mm/day and 0.15 mm/day severally, from the river into the flood plain, although the outlook is that flood plain wetland serves as a wet buffer and supplies the river with H2O during the low season. However, period between July and September 2005, the recharge of flood plain wetland aquifer caused an addition in the volume of H2O storage in the wetlands from 992793 M3s to 1404853 M3. Interaction between the wetland and river is bidirectional, with most of the flow coming out from the river ( Table 1.3 ) , a status that persisted in August and September. The leakage part of flood plain wetland to the river in August was 97.28 millimeter, increasing to 172 millimeters in November as rainfall reduced. In 2005, part of flood plain wetland to the river was 86.01 millimeters, while the river contributed 131.63 millimeter. The period from September 2004 to December 2005, a entire fake recharge of 444 millimeters from HYDRUS-1D applied to the wetland system, out of which 169.21mm leaked into the wetland from the river. Conversely, a sum of 215.03 millimeter leaked out of the wetland system to lend to the nutriment of the White Volta River. In this state of affairs, floodplain wetland contributes as base flow to the White Volta River in the dry season. The entire sum of H2O 556.75 millimeter traveling out of the storage in the 16 month period is merely for the simulation period, and becomes depleted during the dry season. The full rhythm of the kineticss of hydraulic caput simulation to bespeak flood plain wetland and the White Volta River interaction from September 2004 to December 2009 is show in ( Figure 1.9 ) .
Table 1.3 Accumulative mass balance




2004


2005


Sept. 2004-Dec.2005




Inch:


millimeter


millimeter


millimeter




Storage


36.23


61.76


171.87




River escape


2.31


131.63


169.21




Recharge


159.67


221.11


421.64




Sum In


198.21


414.50


762.72




OUT:







Storage


141.33


338.57


556.75




River escape


58.91


86.01


215.03




Entire out


200.24


424.58


771.78




In – Out


-2.03


-10.07


-9.06






During the rainy season between June and September 2005, the hydraulic caput in the Pwalugu flood plain wetlands increased from an norm of 137.79 m to 139.43 m, but started worsening from October 2005 where the hydraulic caput was 138.38 m. The extent, deepness, frequence, timing and continuance of H2O ponding at the surface of the wetlands are of import parametric quantities commanding the extent of dirt wet for the nutriment of the river. For case, ponded H2O in the Pwalugu wetland to a deepness of 0.50 m measured during fieldwork in August 2005 consequences from a complex and variable combination of groundwater upwelling and accretion of rainfall on the concentrated surface. Impregnation of the full wetland was seldom achieved in 2004, because of frequent interruptions in rainfall form with longer dry enchantments. In add-on, the geological formation within the survey country is Voltaian sandstone. The formation is a hapless H2O keeping system, and H2O stored during the rainy season is non readily transmitted to other parts of the system.
The internal conceptualisation of Pwalugu flood plain wetland is based on a semi-confined one-layer system with differing hydraulic features. However, the interaction between the White Volta River and floodplain wetlands takes topographic point in one of these three basic ways: 1 ) rivers gain H2O from influx of groundwater through the river bottom, 2 ) river lose H2O to groundwater by escape through the river bottom or both, or 3 ) river addition in some ranges and lose in others. The mode of interaction between the Pwalugu flood plain wetland and the White Volta River depends upon the procedures commanding the recharge, floodplain morphology and hydraulic belongingss of the system. In this apparatus, the sum of H2O delivered to the H2O tabular array is controlled by the geological formation. Another issue of concern is the appraisal of spacial distribution of recharge, and this can merely be estimated if accurate information on the magnitude and distribution of aquifer belongingss is available.
A correlativity of 0.78 is established between the leaden remainders and weighted simulated values ( Figure 1.12 ) , although they are assumed to be independent of each other. Conversely, the theoretical account was found to hold good identified parametric quantities ; nevertheless the theoretical account consequences were sensitive to the values of input parametric quantities. Therefore, the application of the MODFLOW theoretical account will be more dependable for determination devising.
Decisions
The hydrology of the wetlands found in the basin is complex characterized by spacial and temporal variableness of their volume and surface country.
The White Volta River catchment is sing climatic, hydrologic and flora alterations. This research was conducted to analyze the indispensable function floodplain-wetlands play in watercourse flow within the White Volta basin, in order to guarantee good direction and a sustainable degree of H2O resource use. This research shows that alterations in floodplain-wetland features have branchings on surface H2O flow. Data collected for the survey are derived from field measurings, field observation and research lab analysis.
The hydraulic connexion between the White Volta River and floodplain wetland varies temporally and spatially because of step ining unsaturated zones. To set up the signifier of interaction that goes on between the chief river and flood plain wetlands within the White Volta basin, PM-WIN ( MODFLOW ) was specified utilizing lower boundary discharge from the HYDRUS-1D theoretical account as estimated groundwater recharge. This input quantifies the temporal and spacial fluctuations in the interaction between flood plain wetland and watercourse flow. Prior to simulation, parametric quantities were calibrated to obtain a tolerable distribution of initial hydraulic caput. The standardization procedure reduced the mistake of disagreement from -0.69 to 0. The HYDRUS-1D underside flux used as an estimation of groundwater recharge gave a better tantrum between the fake hydraulic caput and observed sub-surface H2O degree fluctuation. This degree of compatibility gives indicants that the theoretical account standardization needs to be improved.
The simulation of the sub-surface hydraulic caput of the wetland indicates a systematic fluctuation relation to the White Volta River in response to alterations in the rainfall form. The interaction conditions vary from season to season with March, April, and May demoing the least escape ( estimated values of 0.03mm/day, 0.06mm/day and 0.15 mm/day, severally ) from the river into the flood plain, although the outlook is that flood plain wetlands serve as a wet buffer and provide the river with H2O during the low season. Nevertheless, the interaction between the wetland and the river as simulated is bidirectional. With most of the flow coming out from the river, this status persists in the months of August and September.
Mention:
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Beven JK ( 1989 ) Changing thoughts I hydrology- the instance of physically based theoretical accounts. J Hydrol. 105:157-172
Beven JK ( 2000 ) Rainfall-Runoff Modeling: The Premier, John Wiley & A ; Sons Ltd. U.K.
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