Odtnhj

usepackagemultirow
begintable[htbp]
begintabularp2.5cmp2.5cmp1.5cmp6.5cm
hline
multicolumn2ctextbfParameters & multirow2*textbfUsed value & multicolumn1cmultirow2*textbfDefinition \
textbfOriginal & textbfEnglish translation & & multicolumn1c \
hline
Rechenlauf fortsetzen & Continue calculation & No & It determines whether a calculation run is to be continued. If yes, the result data from the file HYDRO_AS 2D.CPR is transferred to the program and used as initial boundary condition. \
Simulationszeit [s] & Simulation time [s] & 86400 & It defines the simulation time in seconds \
Zeitintervall SMS [s] & Time interval SMS [s] & 8640 & It defines the time interval (in seconds) for the storage of area-based result data which can be visualized with the SMS program following the calculations. \
Zeitintervall Q_Strg [s] & Time interval Q_Strg [s] & 900 & It defines the time interval (in seconds) for which the data of the node strings are written to the Q_Strg.dat. \
Hmin & multirow5* & 0.01 m & Minimum water depth \
VELMAX & & 15 m/s & Maximum velocity allowed \
Amin & & 1.e-15 mtextsuperscript2 & Minimum element size allowed for calculating the internal calculation time step \
CMUVISC & & 0.60 & Coefficient cm in the viscosity formula \
SCF & & 1.00 & Coefficient for the additional acceleration of the calculation process \
hline 
endtabular
endtable

A few points:

• use booktabs package for better spacing




• use siunitx package to get the space between values and units right




• use a tabularx to keep the table within the available textwidth, yours was much wider




• subdivide the middle rule




• your parameters seems to be the names of some variables? I'd write them either in typewriter font or in small caps.




• left align the columns. Justified text in very narrow columns will never look good




• you mix if the unit is part of the parameter name of used value. I don't know your program, so no idea what is the correct way, but be consistent




• make the content of the table and the rules aligned by using @

documentclassarticle

usepackagegeometry
usepackagebooktabs
usepackagearray
usepackagemultirow
usepackagetabularx
usepackagesiunitx


newcolumntypeL[1]>centeringraggedrightm#1

begindocument


begintable[htbp]
renewcommandarraystretch1.5
begintabularxlinewidth@L2.5cmL2.5cmL1.5cmX@
toprule
multicolumn2ctextbfParametershspace1em & & \
textbfOriginal & textbfEnglish translation & textbfUsed value & textbfDefinition \

cmidrule(r)1-2 cmidrule(lr)3-3 cmidrule(l)4-4

Rechenlauf fortsetzen & Continue calculation & No & It determines whether a calculation run is to be continued. If yes, the result data from the file textttHYDRO_AS 2D.CPR is transferred to the program and used as initial boundary condition. \

Simulationszeit & Simulation time & SI86400s & It defines the simulation time in seconds \

Zeitintervall textttSMS & Time interval textttSMS & SI8640s & It defines the time interval (in seconds) for the storage of area-based result data which can be visualized with the textttSMS program following the calculations. \

Zeitintervall textttQ_Strg & Time interval textttQ_Strg & SI900s & It defines the time interval (in seconds) for which the data of the node strings are written to the textttQ_Strg.dat. \

Hmin & multirow5* & SI0.01m & Minimum water depth \

textttVELMAX & & SI15m/s & Maximum velocity allowed \

Amin & & SIe-15metersquare & Minimum element size allowed for calculating the internal calculation time step \

textttCMUVISC & & 0.60 & Coefficient cm in the viscosity formula \

textttSCF & & 1.00 & Coefficient for the additional acceleration of the calculation process \
bottomrule 
endtabularx
endtable

enddocument

Here's a solution that's very similar to the one posted by @samcarter. E.g., it uses a tabularx environment, doesn't fully justify the cell contents, and uses the macros num, si, and SI of the siunitx package to display numbers, scientific units, and combinations of numbers and associated units.

Some differences:

• No line breaks allowed in column 3


• Automatic hanging indentation of cell contents in columns 1 and 2


• No bold-facing of header cells


• Terser language in column 4


• Use path macro (provided by url package) to typeset file names


• Use of , (comma) as thousands-separator for numbers with 4 or more digits

documentclassarticle
usepackage[a4paper]geometry % set page parameters suitably
usepackage[hyphens,spaces,obeyspaces]url % for 'path' macro
usepackageragged2e,tabularx,booktabs,siunitx
newcolumntypeL>RaggedRightarraybackslashX
newcolumntypeP[2]>RaggedRighthangafter=1hangindent=1emp#1
begindocument
begintable[htbp]
sisetupper-mode=symbol,
 tight-spacing,
 group-minimum-digits=4,
 group-separator=,
begintabularxtextwidth@ *2P2.2cmlL @
toprule
multicolumn2cParameters & Used value & Definition \
cmidrule(r)1-2
Original & English translation \
midrule
Rechenlauf fortsetzen & Continue calculation & No & Determines whether a calculation run is to be continued. If yes, result data from the file pathHYDRO_AS 2D.CPR is transferred to program and used as initial boundary condition \
Simulations-zeit [sisecond] & Simulation time [sisecond] & num86400 & Simulation time, in seconds \
Zeitintervall SMS [sisecond]& Time interval SMS [sisecond] & num8640 & Time interval (in seconds) for storage of area-based result data which can be visualized with the SMS program following the calculations \
Zeitintervall Q_Strg [sisecond] & Time interval Q_Strg [sisecond] & num900 & Time interval (in seconds) for which the data of the node strings are written to pathQ_Strg.dat \
Hmin & & SI0.01meter & Minimum water depth \
VELMAX & & SI15meterpersecond & Maximum velocity allowed \
Amin & & SIe-15metersquared & Minimum element size allowed for calculating the internal calculation time step \
CMUVISC & & num0.60 & Coefficient cm in viscosity formula \
SCF & & num1.00 & Coefficient for additional acceleration of calculation process \
bottomrule 
endtabularx
endtable
enddocument

This is a slightly off-topic answer, in that others have covered the TeX aspects better than I could and I concentrate on the writing.

You can tighten up the wording of many of the entries in the last column. The "It" at the start of many entries is definitely superfluous. I'd also drop "determines" or "defines" and the "the". You can lose some other articles as well and generally copy-edit your text into a shorter form. I've had a go for you, see below. I may have overdone it in some cases but I still think the first entry is a little wordy. This saves a line on each of all but one of your multiline items, making the whole lot easier to read. Also you've got full stops on some entries but not others.

I'd also add a little vertical space between rows (the total height can still be less within the copy-editing), to make the last column easier to read . Use raggedright to split lines between words rather than hyphenating I've used raggedright for "Continue Calculation", but not for the teo cells starting "Time interval", to demonstrate the effect. These points are covered in other answers, as is the use of texttt which I've inconsistently demonstrated.

In particular line breaks in variable names and the like should really be avoided

defarraystretch1.5%
begintable[htbp]
begintabularp2.5cmp2.5cmp1.5cmp6.5cm
hline
multicolumn2ctextbfParameters & multirow2*textbfUsed value & multicolumn1cmultirow2*textbfDefinition \
textbfOriginal & textbfEnglish translation & & multicolumn1c \
hline
Rechenlauf fortsetzen & raggedright Continue calculation & No & Whether calculation run is to be continued. If yes, results from file textttHYDRO_AS 2D.CPR are transferred to the program and used as initial condition. \
Simulationszeit [s] & Simulation time [s] & 86400 & Simulation time (in seconds) \
Zeitintervall SMS [s] & Time interval SMS [s] & 8640 & Time interval (in seconds) for storage of area-based results which can subsequently be visualized with the SMS program. \
Zeitintervall Q_Strg [s] & Time interval Q_Strg [s] & 900 & Time interval (in seconds) for which data of the node strings are written to textttQ_Strg.dat. \
Hmin & multirow5* & 0.01 m & Minimum water depth \
VELMAX & & 15 m/s & Maximum velocity \
Amin & & 1.e-15 mtextsuperscript2 & Minimum element size for calculating internal calculation time step \
CMUVISC & & 0.60 & Coefficient cm in viscosity formula \
SCF & & 1.00 & Coefficient for additional acceleration of calculation process \
hline 
endtabular
endtable