In the DRASTIC model, which is used to assess groundwater contamination risk, topography is one of the seven key parameters and represents the slope of the land. It affects how quickly water runs off the surface, which influences the recharge of contaminants into the groundwater. Since slope is a direct measure of the steepness of the terrain, it essentially serves as the basis for the topography parameter in the DRASTIC model. Thus, slope can replace topography if accurately measured, as it captures the same influence on runoff and infiltration processes. However, it’s important to ensure that the slope data is detailed and representative of the area to maintain the model's reliability.

In the DRASTIC model, the 'Topography' parameter specifically refers to the slope of the land surface, expressed as a percentage. This parameter assesses how the steepness of the terrain influences surface runoff and the potential for contaminants to infiltrate into groundwater. Therefore, in this context, 'slope' and 'topography' are synonymous, and slope is the appropriate measure for this parameter. (https://www.mdpi.com/2073-4441/12/5/1356?). Slope is often expressed as a percentage because it provides a straightforward representation of the rise over run ratio, making it easier to interpret in practical applications. A slope percentage is calculated by dividing the vertical rise by the horizontal run and then multiplying by 100. For example, a 2% slope means that for every 100 units of horizontal distance, there is a 2-unit vertical rise. This method is intuitive for understanding gradual changes in elevation, which is particularly useful in fields like hydrology and civil engineering. (https://www.omnicalculator.com/math/slope-percentage?). Within the DRASTIC model, 'topography' is quantified using the slope percentage, and expressing slope as a percentage offers a clear and practical way to represent terrain steepness.

INRE:'Percentages versus degrees'. Mostly because of legacy application, 'percentage' is a ratio, basically rise / run, which has been in use because those are immediately available using the crudest tools over thousands of years by surveyors, geologists, civil engineers, etc. ( https://www.sddc.army.mil/sites/TEA/Functions/SpecialAssistant/TrafficEngineeringBranch/BMTE/calcRoadside/roadsideSafetyTutorials/typesOfSlopes/Pages/measuringSlop.aspx )

In modern times, even with super computers, at the most basic level ( over simplification follows ), any math is all operations combining ones and zeros, so addition is fastest, subtraction a little slower, multiplication is tens of times slower than addition, division is ten times slower than multiplication, and trigonometric calculations are 100 times slower and inverse trig functions even slower yet. So, if very simple calculation chains are moving over millions or even billions of cells, it would have a huge impact.