Table 6 Calculations
From: A Method for Resourcing Sustainable Cities in Rwanda Through Informal Settlement Upgrading
Indicator/Notation | Basis of Calculation | Unit | Formula | |
|---|---|---|---|---|
Risk Factors | ||||
Rs | Slope risk factor | Sum of percentage of area on slopes > 10%, with exponentially increasing risk for higher slopes. Minium sum totals to 1; a hypothetical maximum sum would be a risk factor of 17, but this is all but impossible in practice. Realistic maxima are in a 5-10 range. | N/A | (As0/AS) + (2(As10)+(4(As20)+(8(As25)+(16(As30) |
Rr | Rainfall risk factor | Scored 1-5, using integers, based on rainfall level. This 1-5 score relates to the indicator score in the next level of analysis. | N/A | If: r < 1000 mm, then Rr = 1 1000 mm ≤ r < 1200, then Rr = 2 1200 mm ≤ r < 1400, then Rr = 3 1400 mm ≤ r < 1600, then Rr = 4 r > 1600, then Rr = 5 |
Rf | Flood risk factor | The sum of flood, rainfall and overlap hazard factors. | N/A | Zf + Zr+Zv |
Hazard Factors | ||||
Zf | Flood hazard factor | Linearly weighted sum of settlement area within protected wetland zones and incremental flood plains. | N/A | 5(AW/AS) + 4(AR/AS) + 3(Af50/AS) + 2(Af100/AS) |
Zr | Rainfall hazard factor | Multiplied slope & rainfall factors, de-weighted to be half less influential in the floor risk factor than the flood and overlap factors. | N/A | (Rs)(Rr)/8 |
Zv | Overlap hazard factor | Percentage of settlement land area both within a 100-year flood plain and with slopes > 10%. | N/A | Afs/As |
Percentages | ||||
%sd | Percentage of streets with appropriate stormwater drainage | % | Lsd/Lst | |
%Hp | Percentage of the households below the poverty line (if not entered directly) | % | %Hp, or Hp/HS | |
%Hw | Percentage of households with a direct, individual water supply | % | %Hw, or Hw/HS | |
%Ht | Percentage of households with individual appropriate sanitation | % | %Ht, or Ht/HS | |
%He | Percentage of households with access to electricity | % | %He, or He/HS | |
%BO | Percentage of built-up space in a 500 m offset of the settlement | % | BO/(AO-AS) | |
%Ast | Percentage of land allocated to streets in the settlement | % | Ast/AS | |
%Na | Percentage of plots accessible from a public right of way | % | Na/Nl | |
%Gps | Percentage of settlement area within 400 m of an open public space | % | Aps/AS | |
Per Capita & Catchment Indicators | ||||
PH | Average household population | adults | PS/HS | |
Pxw | Population requiring access to public potable water point (rounded to nearest integer) | people | PS-((PS)(%Hw)) | |
Pwmax | Maximum catchment population per water collection point | people | If Nw = 0, then PS; otherwise Nw/PS | |
Pw | Public potable water collection point catchment ratio | Multiple of maximum population per water collection point, per UPC17. | N/A | Pwmax/2000 |
Dw | Public potable water collection point distance ratio | Multiple of maximum required distance to water collection point, per UPC17. | N/A | Pwmax/250 |
Pxt | Population requiring access to public toilet | people | Py-((Py)(%Ht)) | |
Ptmax | Maximum catchment population per public toilet | people | If Nt = 0, then PS; otherwise Nt/PS | |
Pt | Public toilet catchment ratio | Multiple of maximum population per public toilet point, per UPC17. | N/A | Ptmax/250 |
Dt | Public toilet distance ratio | Multiple of maximum required distance to public toilet for all households, per UPCs. | N/A | Dtmax/80 |
Pswmax | Maximum catchment population per solid waste collection point | people | If Nsw = 0, then PS; otherwise Nsw/PS | |
Psw | Solid waste disposal point catchment ratio | Multiple of maximum population per waste disposal point, per UPC17. | N/A | Pswmax/2000 |
Dsw | Solid waste disposal point distance ratio | Multiple of maximum required distance to waste disposal point for all households, per UPC17. | N/A | Dswmax/250 |
Income Levels | ||||
IH | Annual household income defining the poverty line | Multiple of Annual individual income defining the poverty line and average population per household. | RWF | (Ip)(PH) |
Physical Measurements | ||||
Cx | External connectivity ratio | Average distance between primary or secondary distributor roads17 entering/exiting the settlement24. If the settlement is unconnected, the value will return as an extraordinarily high number. | m/node | If Nx = 0, then Lpm/.01; otherwise Lpm/Nx |
A’st | Adjusted land allocated to streets value | 0-100 value of determining the balance of public land available for transport systems, ideally between 6%-36%, per UN CPI25. | N/A | If: %Ast ≤ 0.06, then 0; %Ast > 0.36, then 100; otherwise 100((Ast -0.06)/(0.36-0.06)) |
Yst | Street density ratio | Ratio of length of streets with at least 2 intersections to settlement area, converted (with unit conversion from m/m2 to m/ha). | km/km2 | 1000(Lst2/AS) |
Y’st | Adjusted street density value | 0-40 value indicating proportion of space devoted to streets and public spaces, with 20 being an ideal target, per UN CPI25. | m/ha | If: Yst = 0, then 0; Yst = 40, then 0; otherwise 100(1-|(Yst-20)/20 | ) |
Yi | Intersection density ratio | Number of intersections per area (adjusted from nodes per m2 to nodes per km2), with 100 node/ha being an ideal target, per UN CP25I. | node/ km2 | Ni/((AS)(1,000,000)) |
Y’i | Adjusted intersection density value | Assigns maximum value (100) to Yi if it is already ≥100, otherwise remains as Yi | node/ km2 | If: Yi ≥ 100, then 100; otherwise Yi |
SCI | Street connectivity index | Index as defined in UN CPI25. | N/A | (A’st+Y’st + Y’i)/3 |
YS | Population density of the settlement | p/ha | PS/AS | |
CP | Covered living space per person | m2/p | AC/PS | |
C’P | 20-year projected covered living space per person | Covered living space per person using projected population in 20 years. | m2/p | AC/Py |
GP | Green space per person | m2/p | GP/PS | |
