Remuneración de los instructores externos

A wide range of techniques havebeendeveloped toquantify groundwater-surface

water interactions. The methods can be grouped into the following five categories:

1) directmeasurements of water flux, 2) heat tracermethods, 3) methods basedon

Darcy’sLaw,4)massbalanceapproaches,and5)modelingapproaches. Toachievethe

best representationoflocaland/or regionalstream-aquifer interactions, acombination

of small- and large-scalemethods isrecommended (Brodieet al., 2007;Kalbus etal.,

2006;Menci´oet al., 2014; Rosenberry and LaBaugh, 2008).

2.3.1 DirectMeasurementof Water Flux

Direct measurement of water flux across the stream-aquifer interface can be

accomplished using seepage meters or similar devices. Bag-type seepage meters

are most common and consist of a bottomless cylinder vented to an expandable

plastic bag (Kalbus et al., 2006). The cylinder is inserted into the streambed and

seepage rate ismeasured by calculating thechange in watervolume inthe bagover

a measured time interval. Although seepage meters are an inexpensive technique

for assessing water flux, thebag-type method canlead to inaccuraciesin measured

flux when water flowing over the bag causes it to become distorted (Brodie et al.,

2007). Therefore, numerous types of automatedseepage metershave been developed

to overcome issues related to the collection bags including heat pulse, ultra-sonic,

are useful for identifying groundwater recharge and discharge zones, the applicability

of such instruments instreams islow because of challengesencountered in obtaining

representativeaverageseepagefluxesduetotheinherentvariabilityinstreamdischarge

and hyporheic exchange flow. Additionally, numerousmeasurements arerequired to

effectively characterize flux alonga given stream reach (Menci´o etal., 2014).

2.3.2 HeatTracer Methods

Heat tracermethods can be used to quantify water fluxes at the stream-aquifer

interfaceandtodelineategroundwaterrechargeordischargezones(Menci´oetal.,2014).

Heat tracer methods are appealing because they necessitate little to no alteration

of the environment (Somers et al., 2016). Such methods utilize fiber-optic cables

or node-like temperature loggers installed in the water column to record stream

temperature(Somers et al., 2016). Stream temperatures varyon a daily andseasonal

basis, whereasthe temperatureofgroundwater remains relativelyconstantthroughout

the year if there is limited groundwater pumping and evapotranspiration (Anderson,

2005;Kalbus etal., 2006). Temperature monitoring in thestream and surrounding

sediments can therefore indicate gaining and losing stream reaches (groundwater

discharge and recharge zones, respectively). Furthermore, when combined with an

analytical or numerical solution forthe heat transport equation, heattracer methods

can be used toquantify seepage fluxes throughstreambed sediments (Brodie et al.,

2007; Somers et al., 2016). Information on the movement of heat also helps to

constrain the calibration of a groundwaterflow model by providing additional data

(Anderson, 2005). The use of temperature measurements in groundwater research

has beensporadic, butwith improvedtemperature sensors andnumerical codes, its

usefulnessinhydrogeologicalsettingsisbeginningtoberevealed. Forexample, Suetal.

environmental tracer inthe Russian River, Sonoma County, California. Somerset al.

(2016) used heattracer methodsand a deterministic numericalstream temperature

model (HFLUX) to quantify the groundwater contributions to the Quilcay River, and

to understand the interactionbetween groundwater and surfacewater in aproglacial

valleyof the CordilleraBlanca, Peru.

2.3.3 Particle Size Analysisand Hydraulic Tests

Methods basedon Darcy’sLaware themost commonlyusedtoinvestigate ground-

watermovementin terrestrialaquifers (Kalbusetal.,2006;Menci´oet al.,2014). These

methodsrequirepointmeasurementsofthecomponentsoftheDarcyequation(Eq.2.3)

includingthehydraulic conductivityofthe aquiferandthehydraulicgradientbetween

the stream and the aquifer (Menci´o etal., 2014; Rosenberry and LaBaugh, 2008).

Determining the hydraulicconductivity of aquifermaterial canbe accomplishedin

alaboratory settingby performing grain-size analysesof sedimentsamples. Hydraulic

conductivitycanbederived fromthegrain-sizedistributionofasedimentsampleusing

empirical relationsbetween grain sizeand permeabilitysuch as theHazen (1892) or

Kozeny(1927) and Carman (1956)(Kozeny-Carman) equations. However, empirical

methods have been found to produce poor estimates when compared to measured

valuesfor several reasons the primary beingthat each equation ismost applicable for

the type of sediment used to derive it (Bradbury and Muldoon, 1990; Rosas et al.,

2014;Sahu and Saha, 2016).

Hydraulic conductivity can alsobe estimated from measurements of flow rate and

headinapermeameterfilledwithaquifersedimentsundersteady-state(constanthead)

or transient (falling head) conditions(Kalbus et al., 2006). Although permeameter

testsareeffectiveat determiningrelative differencesin hydraulicconductivitybetween

when comparedto valuesmeasured in situ. This islikely because sediment grains are

rearrangedwhenpackedintothepermeameterandlarge-scalefeaturessuchasfractures

and bedding arenot captured at the scale of thepermeameter sample(Bradbury and

Muldoon, 1990).

Alternatively, hydraulic conductivity can be determined by performing pumping,

slug,orbailtestsinawell. Duringapumpingtest,waterisabstracted fromawellata

constantrateanddrawdown(thechangeinhydraulicheadfromsomeinitialstateinan

aquifer)ismeasuredasafunctionoftime. Duringaslugorbailtest,aknownvolumeof

water isdisplacedor removed fromthe well,and as the waterlevel recovers,hydraulic

head is measured as a function of time (Kalbus et al., 2006). Several researchers

(Cardiffetal., 2011;Fox,2004;Hunt etal.,2001; Hunt,2003;KolletandZlotnik,2003;

Lough and Hunt, 2006; Nyholm et al., 2002, 2003; Poulsen et al., 2011) have used

such techniques in a rangeof hydrogeological settingsto estimateaquifer hydraulic

conductivity and to determine degree of stream-aquifer connectivity. Several of these

authors have made significant contributions to our understanding of groundwater-

surface water interactions by improving the applicability of established analytical

modelsandbyhighlighting someimportantfindingsfuture researchersshouldconsider.

For example, Poulsen et al. (2011) found that an important component inparameter

estimation bypumpingtestanalysisforunconfined aquiferswhenthe drainageprocess

is delayed is the use of a model that accounts for time-varying drainage from the

vadose zone (such as the models of Mishra and Neuman (2010) and Malama et al.

(2011)). KolletandZlotnik(2003)discoveredthatstreambedandaquiferheterogeneity

isthemajor cause fortheinconsistencies inparameter andstreamdepletion estimates.

LoughandHunt (2006)foundthatpumpingtestsmustbecarriedoutforasufficiently

longperiod oftime to allowleakage fromthe streamto have asignificant influence on

The other component of Darcy’s Lawrequired for the determinationof water flux

in the subsurface isthe hydraulicgradientbetween the streamand theaquifer. Deter-

mining the hydraulicgradient isusually accomplishedby measuring andcomparing

the waterlevel in wells andpiezometers installed in the fluvial plain to those installed

in thestream. Piezometers,with pressure transducers installed in them,provide point

measurementsof hydraulic headand have becomea standard method to determine

hydraulic head. The vertical and horizontal components of groundwater flow can be

determinedfromdifferencesinhydraulicheadbetweenindividualpiezometersinstalled

inclusters and at various depths(Kalbus etal., 2006). It has been shown that more

thanone piezometer or piezometer cluster isneeded forparameter estimation and for

evaluatingstreamdepletionrate(Kalbus etal.,2006;KolletandZlotnik,2003;Menci´o

et al., 2014). Baxter et al. (2003) proposed a new method for installing numerous

mini-piezometers in gravel and cobble streambeds to measure hydraulic head and

to estimate streambed hydraulic conductivity. Hydraulic potentiomanometer mea-

surements provideanadditional technique for measuring the vertical hydraulic-head

gradient beneath a surface water body and for estimating hydraulic conductivities

(Rosenberry and LaBaugh,2008). Lamontagne etal. (2014) successfully used adrive

point and manometersystem to measure pressure gradientsand estimate infiltration

through a riverbed ina semi-arid river basin insoutheastern Australia.

2.3.4 MassBalance Approaches

Mass balance methodologies have been developedbased onthe assumption that

anychange in the propertiesof surface water, or anygainor loss ofsurface water, can

be relatedto awater source, and,thus, the groundwatercomponent can beidentified

(Kalbus et al.,2006; Menci´o etal., 2014; Rosenberry and LaBaugh,2008). Method-

and solute tracer techniques. Theincremental streamflow method involves measuring

streamflow discharge at successive cross-sections during low flow conditions, and

associatingany change instreamflow to groundwater recharge ordischarge (Kalbus

et al., 2006). Thehydrograph separation technique has been the most widelyused of

the mass balance approaches due to the accessibility of data and involves separating

a stream hydrograph into its distinct runoff components, and then assuming that

baseflowsignifies groundwaterdischarge into the stream. Severalresearchers (Nyholm

etal., 2003; Rugel etal., 2012; Weberand Perry, 2006)have successfully used hydro-

graph separationto estimate streamflow depletion in vastlydifferent hydrogeological

environments. Hydrologicaltracers canbeusedto characterizewaterdynamics within

awatershedorstreamreachbydeterminingmixingandflowpaths,residencetime,and

inputs andoutputs within asystem (Rosenberry andLaBaugh, 2008). Environmental

tracer techniques utilize concentrations of isotopic and geochemical tracers, whereas

solute tracermethodsinvolve injecting a known amount of aconservative tracerinto

a stream or well. It has been noted that acombination of hydrologic data and tracer

tests produce the most reliable results(Kalbus etal., 2006; Menci´oet al., 2014).

In document Manual de procedimientos para las áreas temáticas en los ejes estratégicos de Vinculación Empresarial, Transferencia Tecnológica y Educación Continua del Centro de Transferencia Tecnológica y Educación Continua (página 120-132)