Purpose of the web- based rainwater harvesting toolkit. What does the Rainwater Harvesting Toolkit DO and what does it NOT DO?

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1 User s Manual Purpose of the web- based rainwater harvesting toolkit The Rainwater Harvesting Toolkit was developed to provide quantitative, locally specific information about water yield of rainwater harvesting systems composed of a rain water catchment (a rooftop or a natural small watershed) and a storage (tank or a small dam). That information is presented in a way that facilitates: assessment of adequacy of a rainwater harvesting system to satisfy particular water needs designing the system (sizes of catchment and tank/dam) in a cost- effective manner What does the Rainwater Harvesting Toolkit DO and what does it NOT DO? The Rainwater Harvesting Toolkit s focus is on those aspects of rainwater harvesting system's design that affect how much water does the system provide at a particular location, i.e. on the catchment area and the volume of storage. The Rainwater Harvesting Toolkit DOES provide information on HOW BIG should the roof/catchment and tank/dam should be for the system to optimally meet your water demand. The design of the rainwater harvesting system does, however, involve several other elements, such as appropriate gutters, plumbing, filters etc., and its operation should be carried out with care, knowledge and understanding in order to provide safe (clean) water. The Rainwater Harvesting Toolkit, DOES NOT provide information on WHAT should the exact configuration and components of your rainwater harvesting system be, and HOW to connect and set them up. There is a wealth of information on those aspects of rainwater harvesting available on the internet, conveniently provided by commercial and non- profit organizations. Please use those sources too, before you decide whether or not to implement a particular design of a rainwater harvesting system in your house/farm/context. What to expect from the Rainwater Harvesting Toolkit?

2 Rainwater Harvesting Toolkit allows for an interactive assessment of performance of a rainwater harvesting system, and in particular: evaluating how do the rainwater harvesting system's design parameters (i.e. size of the roof/catchment and volume of tank/dam) influence the amount of water that could be obtained from it, comparing water supplied from rainwater harvesting system under different sizes of catchment and different storage volumes with the user's water demand (or current use), visualizing what one can expect from the rainwater harvesting system in an average, dry and wet conditions, assessing various design options to cope with year- to- year and seasonal climate variability. Intended audience The Rainwater Harvesting Tool targets a broad range of users: technical users involved in design and planning of rainwater harvesting systems at household or municipality levels, individuals planning implementation of a rainwater harvesting system for a household or a small farm, educators at all levels, looking for resources facilitating exploration of water conservation measures, as well as for quantitative information allowing assessment of rain water as a water resource.

3 Navigation Navigation of the Rainwater Harvesting Toolkit is based on the traditional menu that facilitates a step- by- step procedure of defining rainwater harvesting system s parameters. The user can proceed to the next step (menu tab) once they have provided necessary information. They may, however, go back to the previous steps (menu tabs) and revise the information given there. Design tab provides a general information about the design of rainwater harvesting systems. Context tab provides a choice of application - either simple assessment of rainwater harvesting potential, designing of the rooftop rainwater harvesting system, or designing a small dam- based rainwater harvesting system. Location tab provides an interactive map allowing selection of geographical location for the rainwater harvesting system. Specifications tab allow for defining system design parameters such as rooftop size, storage volume etc. Current usage tab allows for defining water use volumes and temporal water use pattern. Results tab contains graphs visualizing results of calculations. It also allows for changing the basic system design parameters with immediate adjustment of graphs visualizing system s performance. NOTE: Menu tabs Specifications and Current Usage are accessible ONLY in they are relevant in a particular context, i.e. they will not be available if user has selected Quick Assessment option. NOTE: Results tab is accessible ONLY when all required parameters of the rainwater harvesting system are defined by the user.

4 Obtaining additional information/contextual help Each page contains links to help that describe in more detail the items on that page. These are marked by: These link to a wealth of information that helps understand the complexity and implications of various aspects of rainwater harvesting system design. Typical workflow Below we describe typical workflows and options/choices/information requirements the user will face under each of the use cases for which the Rainwater Harvesting Tool was designed, namely Quick assessment of rainwater harvesting potential for a particular location Calculations of water yield from rooftop rainwater harvesting system Calculations of water yield from small dam rainwater harvesting system

5 Use case: Quick assessment of rainwater harvesting potential Step 1: Select the Quick assessment.. under the Context tab: Step 2: Define the geographical location of the site for which you want to assess rainwater harvesting potential under the Location tab:

6 To select your location, pan and zoom on the map until you find the location. A single click on the map will put a marker at the selected place, and geographic coordinates of that place will be displayed above the map: You may change the position of the marker by clicking at another place on the map, until you are satisfied with its location. Note: You may use the Auto Locate button to automatically find your location on the map. You may be asked if you agree with Google accessing some information on your computer. This request does not originate from our website, but from the Google servers. It is in general safe to agree to that request, but if you have any reservations, you may refuse. In such a case, you will have to determine your location manually. Note: The Auto Locate feature may not be very accurate. You should check the positon of the marker and adjust it if necessary. Note: The button displays a page that explains why it is important to accurately determine location of the rainwater harvesting site.

7 Step 3: Display the results of the rainwater potential calculations by selecting Results tab: The results of the quick assessment are provided as a total amount of water that a rainwater harvesting system can potentially generate in an average year, as well as in the form of a graph illustrating amount of water that the system can provide in each month. Note: The values displayed on the Results page are potential values, i.e. such that can be obtained when there are no water loses in the system and when all the rainwater that reaches the roof/catchment can be stored for later use. The actual, real system may not achieve this level of efficiency, and the amount of water that can be obtained at a particular location by a system with a particular design needs to be assessed using one of the two other modes of the Rainwater Harvesting Toolkit that are selected under the Context tab. Note: The buttons display pages explaining what the information on the Results page mean and how to interpret it.

8 Note: The graph presents the amount of potential rainwater captured in an average conditions. Selecting the dry-wet range button will show the amount of water harvested during wet and dry conditions: Note: The graph can be printed or saved on your computer for future reference by clicking on the button in the top right corner of the graph.

9 Use case: Rooftop rainwater harvesting system Step 1: Select the Design of a roof top water harvesting.. under the Context tab: Note: Upon selecting this option, a list of necessary inputs is shown in the header of the page. All elements marked in red need to be provided by you under the Location, Specifications and Current Usage tabs. The Results tab will be accessible only if all the elements are provided. Step 2: Define the geographical location of the site for which you want to design rooftop rainwater harvesting system under the Location tab:

10 To select your location, pan and zoom on the map until you find the location. A single click on the map will put a marker at the selected place, and geographic coordinates of that place will be displayed above the map, as well as in the input summary section: You may change the position of the marker by clicking at another place on the map, until you are satisfied with its location. Note: You may use the Auto Locate button to automatically find your location on the map. You may be asked if you agree with Google accessing some information on your computer. This request does not originate from our website, but from the Google servers. It is in general safe to agree to that request, but if you have any reservations, you may refuse. In such a case, you will have to determine your location manually. Note: The Auto Locate feature may not be very accurate. You should check the positon of the marker and adjust it if necessary. Note: The button displays a page that explains why it is important to accurately determine location of the rainwater harvesting site.

11 Step 3: Specify parameters of the rooftop rainwater harvesting system under the Specifications tab: Note: The buttons display pages that explain significance of individual parameters and show how to obtain them for your household. Note: Filling in the individual parameters will change values show in the input summary section in the top of the page. The values you are providing are checked for being realistic Step 4: Define your current water usage or planned water demand under the Current Usage tab:

12 This page allows for supplying of information on water demand in a tiered way. One has to firstly select the appropriate household type, which will select water demand figures for a typical household of that type: One can proceed with these figures, or modify them appropriately. Note: The figures defined in the household section represent mean monthly usage, and if accepted, calculations will be carried out considering identical water demand in each calendar month. If one has a more precise knowledge of water demand figures on the month-to-month basis, these can be provided under the Total usage in calendar months. For this, one needs to unfold the monthly usage section by selecting that option: This section provides a table where values of individual months demand can be entered, as well as a graph that visualizes the figures. Note: Garden watering figures can be automatically adjusted to reflect different amounts of irrigation required during different months because of differences in air temperatures by selecting the tick-box. The amounts will NOT, however, be adjusted for the amount of rainfall occurring in each of the months. If you irrigate less during the rainy season, you have to adjust the irrigation figures accordingly. Note: The buttons display pages that explain significance of individual parameters and show how to obtain them for your household.

13 Step 5: Viewing results of calculations of rainwater harvesting system s performance under the Results tab: In that section, the buttons on the left-hand side display a number of different graphs illustrating aspects of the rainwater harvesting system s performance under given parameters i.e. roof size, tank size and water demand, e.g:

14 Note: The graph presents the amount of potential rainwater captured in an average conditions. Selecting the dry-wet range button will show the amount of water harvested during wet and dry conditions: Note: The graph can be printed or saved on your computer for future reference by clicking on the button in the top right corner of the graph. Note: The buttons display pages that explain information visualized in individual graphs. Step 6: Adjusting design parameters (if necessary) This can be carried out by adjusting the Tank volume and/or Roof area sliders in the Results tab, or alternatively, going back to the Specifications or Current usage tabs, and changing parameters there and then returning to the Results section. In a context of a typical design process, parameters may be adjusted by the user so that optimal performance of the system is achieved. By changing these parameters, user may assess the effects of increasing/reducing size of the tank, or connecting additional sections of the roof into the system would have on the amount of water obtained from the system.

15 Use case: Small Dam rainwater harvesting system Step 1: Select the Design of a small dam system.. under the Context tab: Note: Upon selecting this option, a list of necessary inputs is shown in the header of the page. All elements marked in red need to be provided by you under the Location, Specifications and Current Usage tabs. The Results tab will be accessible only if all the elements are provided. Step 2: Define the geographical location of the site for which you want to design small dam rainwater harvesting system under the Location tab:

16 To select your location, pan and zoom on the map until you find the location. A single click on the map will put a marker at the selected place, and geographic coordinates of that place will be displayed above the map, as well as in the input summary section. Additionally, a topographical catchment surface runoff from which flows to the selected location is delineated, and its area (in ha) determined: You may change the position of the marker by clicking at another place on the map, until you are satisfied with its location. Note: You may use the Auto Locate button to automatically find your location on the map. You may be asked if you agree with Google accessing some information on your computer. This request does not originate from our website, but from the Google servers. It is in general safe to agree to that request, but if you have any reservations, you may refuse. In such a case, you will have to determine your location manually. Note: The Auto Locate feature may not be very accurate. You should check the positon of the marker and adjust it if necessary. Note: The button displays a page that explains why it is important to accurately determine location of the rainwater harvesting site.

17 Step 3: Specify parameters of the rainwater harvesting system under the Specifications tab: Note: In the parameter specification section catchment area and catchment soils will be picked up automatically based on your site selection. These values are determined from relevant soil and topographic data. Note: The buttons display pages that explain significance of individual parameters and show how to obtain them for your household. Note: Filling in the individual parameters will change values show in the input summary section in the top of the page. The values you are providing are checked for being realistic

18 Step 4: Define your current water usage or planned water demand under the Current Usage tab: This page allows for supplying of information on water demand in a tiered way. One has to firstly select the appropriate household type, which will select water demand figures for a typical household of that type: One can proceed with these figures, or modify them appropriately. Note: The figures defined in the household section represent mean monthly usage, and if accepted, calculations will be carried out considering identical water demand in each calendar month.

19 If one has a more precise knowledge of water demand figures on the month-to-month basis, these can be provided under the Total usage in calendar months. For this, one needs to unfold the monthly usage section by selecting that option: This section provides a table where values of individual month s demand can be entered, as well as a graph that visualizes the figures. Note: Garden watering figures can be automatically adjusted to reflect different amounts of irrigation required during different months because of differences in air temperatures by selecting the tick-box. The amounts will NOT, however, be adjusted for the amount of rainfall occurring in each of the months. If you irrigate less during the rainy season, you have to adjust the irrigation figures accordingly. Note: The buttons display pages that explain significance of individual parameters and show how to obtain them for your household.

20 Step 5: Viewing results of calculations of rainwater harvesting system s performance under the Results tab: In that section, the buttons on the left-hand side display a number of different graphs illustrating aspects of the rainwater harvesting system s performance under given parameters i.e. roof size, tank size and water demand, e.g: Note: The graph presents the amount of potential rainwater captured in an average conditions. Selecting the dry-wet range button will show the amount of water harvested during wet and dry conditions:

21 Note: The graph can be printed or saved on your computer for future reference by clicking on the button in the top right corner of the graph. Note: The buttons display pages that explain information visualized in individual graphs. Step 6: Adjusting design parameters (if necessary) This can be carried out by adjusting the Reservoir volume slider in the Results tab, or alternatively, going back to the Specifications or Current usage tabs, and changing parameters there and then returning to the Results section. In a context of a typical design process, parameters may be adjusted by the user so that optimal performance of the system is achieved. By changing these parameters, user may assess the effects of increasing/reducing the size of the dam/reservoir as well as usage pattern on the amount of water obtained from the system.

22 Interpretation of results Quick assessment of rainwater harvesting potential In this use case/mode, only very general information about a rainwater harvesting system is generated. This is meant for you to be able to assess whether the rainwater harvesting system at your house/garden/farm makes sense at all. The values provided in the Results section pertain to the volume of water that can potentially be obtained from 100m2 of the catchment area. If you have a general idea about how big your catchment/roof is, you can quickly see whether the amount of water captured by the rainwater harvesting system can potentially be a substantial fraction of your need. You can also assess how much water could you potentially obtain if you captured all rainfall falling within the entire footprint of your property etc. Importantly, the Quick assessment mode should be followed by analyses carried out in the Rooftop or Small Dam modes, as these provide a much more realistic assessment of water yield of a rainwater harvesting system. Rooftop rainwater harvesting system You should view and read about every graph in the results section, as the graphs will help you understand how your rainwater harvesting system works. Essentially, the most important graph is the "percent of need supplied". It shows how much of your monthly demand (or need) will be provided by the rainwater harvesting system. By watching the values change as you manipulate the roof size and tank volume sliders you can see how much you improve (or reduce) your supply. Changing roof size (here by slider, but in real life by, for example, designing, or redesigning your gutters system so that roof sections that drain separately now drain into the tank) will increase the amount of rain water available. Similarly, increasing tank volume you can increase the length of time during which rain water will be available after rain events. But obviously such changes come at a cost. You have to assess whether these costs will be offset by the amount you save on water bill. Notably, you may notice that there is a threshold wrt. the tank size, i.e. there is a certain tank volume, for which all, or majority of water available from a given roof size is captured. It does not make sense to use tank bigger than this volume, because having a bigger tank will not increase the amount of rainwater captured by the system. Small dam rainwater harvesting system Similar to the rainwater harvesting mode, you should view and read about every graph in the results section, as the graphs will help you understand how your rainwater harvesting system works. Essentially, the most important graph is the "percent of need supplied". It shows how much of your monthly demand (or need) will be provided by the rainwater harvesting system. By watching the values change as you manipulate the roof size and tank volume sliders you can see how much you improve (or reduce) your supply.

23 Obviously, in the small dam-catchment rainwater harvesting system you are not able to manipulate catchment parameters. Only the location and volume of the dam may be designed. By increasing dam volume, you can increase the length of time during which rain water will be available after rain events. But obviously such changes come at a cost. You have to assess whether these costs will be offset by the amount you gain from increased water availability. In the context of agricultural application, the figures showing dry-wet range are critical. Considering that we have based our calculations on 45 years of rainfall data, the figures for dry conditions represent the water supply levels that you may expect to occur only once in 45 years, and you may consider this information in the design of the system and your agricultural activities, as it determines the level of risk in your system. Notably, you may notice that there is a threshold wrt. the dam size, i.e. there is a certain dam volume, for which all, or majority of water available from a given catchment is captured. It does not make sense to use dam bigger than this volume, because having a bigger dam will not increase the amount of rainwater captured by the system. This of course applies to a small hillslope dam, or a headwater dam. In the situation of a dam on a substantial stream, one should consider ecological flow releases.

24 Technical Documentation Datasets underlying the rainwater harvesting tool Rainfall and climate data CHIRPS 2.0 satellite rainfall product Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) is a 30+ year quasi- global rainfall dataset available from Spanning 50 S- 50 N (and all longitudes), starting in 1981 to near- present, CHIRPS incorporates 0.05 resolution satellite imagery with in- situ station data to create gridded rainfall time series that was originally intended for trend analysis and seasonal drought monitoring. For daily Africa data CHIRPS is also available as a 0.25 x 0.25 degree (approximately 25 by 25 km) spatial resolution product, and that product has been used in the current version of Rainwater Harvesting Toolkit. In spite of the overall good quality of the CHIRPS product, our analyses revealed that is contains biases. For the purpose of Rainwater Harvesting Toolkit, the 0.25deg CHIRPS product has been bias corrected based on the data from 1700 rain gauges available at UCT CSAG s database. That bias- correction procedure was developed so that spatially continuous fields of daily rainfall could be obtained that are consistent on a monthly basis with observational (station) data in terms of frequency and sequencing of rain and no- rain days as well as range of rainfall intensities. The bias- correction procedure involved: Derivation of parameters of Markov chain describing transitions between rain days and no rain days on a month- to- month basis, as well as parameters of gamma distribution describing distribution of daily rainfall values, for each station, as well as for CHIRPS grid cells corresponding to the stations locations. Derivation of correction coefficients for Markov chain parameters for each station location and for each calendar month. Interpolation of correction coefficients between stations using ordinary kriging. Interpolation of station- derived parameters of gamma distribution. Generation of time series of daily rainfall for each of CHIRPS grid cells based on the interpolated Markov chain parameters and gamma distribution parameters. The bias- correction method reduced biases of CHIRPS to the level that is consistent with uncertainty levels resulting from natural variability.

25 WATCH WFDEI We have decided to base our calculations of evaporative loses from dam/reservoir as well as evaporative demand of irrigation systems on WATCH WFDEI (Weedon et al. 2010) dataset ( watch.org/). This dataset has advantage of regional (in fact global) coverage, and internal consistency between variables. Its drawback is a relatively low spatial resolution, namely 0.5 by 0.5 degrees. However, considering that air temperature does not display strong spatial variability (unless in mountainous environments), this dataset seems appropriate for the intended purpose of the Rainwater Harvesting Toolkit. Topography SRTM m resolution dataset ( is used as a basis for delineation of the catchment area based on user selected location. That dataset became available globally in 2014, and supersedes the earlier 90m resolution data. The SRTM digital elevation data were used to generate the flow direction map. That was done using Channel Network and Drainage Basin function of the SAGA library in the QGIS (Pisa) software. Soils Soil data are necessary to calculate runoff from a given rainfall. Soil maps with soil typology and textural information available from global databases, Harmonized World Soil Database (FAO/IIASA/ISRIC/ISS-CAS/JRC, 2012), and ISRIC database (ISRIC, 2013), are used to provide textural information and parameters such as bulk density and water holding capacity. For South Africa we use hydrological soil group map derived for quinary catchments by Schmidt and Schulze (1987) obtained from the Quinary Catchments Database supporting ACRU model at UKZN. Rooftop case methodology and algorithm The calculations of water budget are performed on the daily basis according the following formulas: S "#$ = min (S +,-, Q " min Q ", D " ) Q " = S " + max 0, c P " A f where S t and S t+1 and are tank storage at the beginning and at the end of the day, P t is rainfall during the day, A is roof area, c is roofing material- specific runoff coefficient, f is volume retained in the first flush mechanism and Q t is water available during the day to satisfy demand, and D t is water demand during that day. The formulas impose limitations of day- to- day storage not exceeding the volume of the tank, and maximum daily actual water use to not exceeding water available in the tank during that day. Overflow (O t ) is defined as: O " = max (Q " min Q ", D " S +,-, 0) and supply deficit is defined as: SD " = min Q " D ", 0

26 After calculating water budgets for each of the days for which rainfall data are available, the elements of the water budget are used to calculate performance indices on the month- to- month basis. The indices are as follows: - Total water supply - Percent satisfied demand - Volume needed to satisfy demand - Runoff from roof - Days with no water in the tank These indices are subsequently summarized to illustrate their average value during each of the calendar months (also known as climatology). Also, the minimum and maximum value for each index and each calendar month are derived. These are illustrated in the figures in Results section of the Rainwater Harvesting Tool. Small dam methodology and algorithm Delineation of catchment draining to the user- selected location Catchment delineation is carried out based on DEM data SRTM 4.0 (30m resolution), using the following approach: - First, the DEM is used to derive cell- to- cell flow direction. The concept adopted here is that of many- to- one, i.e. flow into a cell can occur from many neighboring (upstream) cells, while all outflow from that cell flows only into a single neighboring (downstream) cell. This step is pre- calculated with a modified maximum slope- based D8 algorithm. The modification accounts for a situation when identical maximum downstream slope is detected towards two different cells. - Subsequently, catchment is delineated for a selected cell (location) with an algorithm that tracks flow direction out of cells neighbouring that cell. This is done in run- time, i.e. after the user has selected location of the dam from a map, or satellite image. Calculations of loses from the dam/reservoir. Unlike for a tank used in rooftop case, water balance calculations within the Small Dam module have to account for water loses from the dam that occur due to infiltration to the ground, and evaporation to the atmosphere. In our implementation, infiltration rate from the dam reservoir is related to the soil type. A simple relationship is used based on literature data (e.g. De Hammer et al. 2008): - For soil types A, A/B and B infiltration is 2 mm/day - For soil types B/C, C, infiltration is 1 mm/day

27 - For soil types C/D and D, infiltration is 0 mm/day Infiltration is calculated as a function of the water surface area (explained below). Evaporation from open water surface of the dam is calculated based on open water evaporation (E 0 ) climatology. That climatology can be obtained using several data sources and several methods, and here, we have decided to use FAO Penman- Monteith method (Allen et al. 1999) based on WATCH WFDEI data (Weedon, 2010). Penman- Monteith method comprehensively accounts for a number of variables affecting evaporation (temperature, wind, humidity) and WATCH WFDEI dataset provides a regional, consistently- determined set of variables needed by this method. Actual evaporation from the dam is calculated as a function of E 0 and water surface area of the dam: LOSS Evap = E 0 *A The latter is determined from the actual volume of water stored in the dam from the volume- area relationship. Volume- area relationship is usually calculated from topographic data, but the regional SRTM 4.0 dataset available does not provide resolution and accuracy that would be suitable in a small dam context. Instead we have decided to use a simplified approach, in which we pre- define three classes of volume- area relationship, and task user with selecting the appropriate one. The three classes, defined based on small dam studies in Limpopo basin ( are as follows: - Deep with steep sides and flat bottom, described by the following equation: V=0.030*A Moderate with moderately inclined bottom and sides: V=0.025*A Shallow with gently- sloping sides and poorly defined bottom: V=0.020*A1.32 Runoff from the catchment Calculations of runoff from catchments are based on the SCS CN approach. The SCS CN method was developed originally in 1956 (described in detail in Mishra & Singh, 2003) by US Soil Conservation Service for hydrological and soil conditions prevalent in US. The method has been adaptated to reflects specific hydrological properties of South African soils, characterized through work by Schmidt & Schulze (1987). The method forms the basis of the commonly used ACRU agro- hydrological model, and is one of the methods used in design flood estimation (Smithers, 2012), and has been used earlier in the determination of rainwater harvesting potential in South Africa (de Winnaar et al. 2007), and in Africa (Senay and Verdin, 2003). The SCS - SA method is particularly suitable for computing flood peaks and run- off volumes for catchments smaller than 30 km 2 and with slopes of less than 30 per cent. It is mainly applicable to rural catchments but may also be used for urban areas. The SCS - SA method takes into account most of the factors that affect runoff, such as quantity and temporal distribution of rainfall, land use, soil type, prevailing soil moisture conditions, and size and characteristics of the catchment.

28 The version applied here is described in SANRAL Drainage Manual (2013). It utilizes land use classes adapted to the typical land cover in South Africa, including agricultural lands, and soil classes encountered in South Africa. It also includes modification of curve number to reflect influence of antecedent moisture conditions on the runoff generation. Hydrological soil classes for the application of this method are derived from dataset for quinary catchments in RSA (developed for SANRAL, 2013). Outside of RSA, hydrological soil classes are derived from textural classification of dominant soils obtained from Harmonized World Soil Database, and its translation to infiltration classes using pedo- transfer function by Cosby et al. (1984). Importantly, in the implementation within the Small Dam module to rainwater harvesting tool, the soil hydrological class can be modified by the user based on the description of soil classes. This gives the user an opportunity to refine the soil characteristic obtained from the regional datasets.