Water tax is based on how many cubic metres of water a household uses. Generally, water tax is based only on water consumption intake shown in water meter and does not include rainwater going to drain pipes. A substantial quantity of storm water is drained via sewer systems and go through the same drain pipes where untreated household water is flowing. With this criteria, commercial establishment pay very less water tax as they have a very limited water usage but throw a large amount of water into the drains. This project aims to present a smart and innovative way to restructure water tax by taking into account storm water along with tap water. It is in this context that our project proposed a new logical basis by including storm water in the water tax. This restructuring on the water tax is based on the amount of water calculated for each property using GIS and Photogrammetry technologies.
For approximate calculation of amount of storm water, it is important to know the area of different surfaces (here it is called sealed areas) and its run off coefficient. InSell has collective experience of photogrammetric data processing which primarily includes demarcation of sealed areas using photogrammetric AT and 3D compilation for many German cities and with the help of GIS impervious surfaces are measured and calculated for each property.
The next stage is to propose a new water tax i.e. restructuring the water tax to all the households which will be calculated based on size and type of property. Therefore, an intensive verification is needed to scrutinize the water tax for each property which mainly focuses on single family residences, multi-storey houses and commercial properties.
The management of water resource is an essential key planning of cities as it is an indispensable component of human life. Nowadays, public authorities, municipalities with the collaboration of public and private companies understand that the management of this precious resource through technologies and smart tools is fundamental in order to guaranty the durability and quality of water resource.
In Germany, the water quantity problems are rather unusual thanks to its favourable climatic geographical situation. With an annual of rainfall varies from 563 mm to 855 mm, storm water makes a significant contribution to groundwater recharge. On sealed areas, storm water is mostly drained through sewer systems which are also used for untreated household water.
In the water tax, only the number of cubic meters of water a household uses are calculated but all of the amount of rainwater flowing and drained on properties, are not consider in the water tax. This basis of calculate water tax imbalance the price between the different types of built-up areas. For example, commercial establishment occupied a large area but pay very less water tax as they have a very limited water usage but throw a large amount of water into the drains. Regarding this context, this problem statement aims to propose a new logical basis by including storm water in the water tax. This restructuring on the water tax is based on the amount of water calculated for each property type and role of geospatial technology is crucial in this context.
In order to calculate the amount of water run off on each property, an evaluation and demarcation of sealed areas according to the size and type of the property was required. Demarcated Impervious surfaces are measured and calculated with the help of GIS and photogrammetry system. After this stage completed, an intensive analyse of the data is conducted to provide a new logical basis for water tax for each property type and household.
Water Tax restructuring project has following key stages:
1. Conceptual basis to restructure water tax
2.Use of Photogrammetry and GIS to capture and analyse information
3.Preparing Proposal for citizen to calculate their own water consumption.
InSell is further extending its scope to develop a concept for smart water tax management by utilising this information.
Stage 1: Conceptual basis to restructure water tax
Why restructuring the water tax? The existing water tax is based only on tap water consumption and do not considered storm water. Yet, the quantity of storm water flowing on impervious areas and drained via drain pipes is much more important than untreated water used by households. In urban areas, storm water consists of water from rain which fall on streets, paved roads, parking lots, building’s rooftops and other developed surfaces but its drainage, through sewer systems, is not included in the water tax.
This non-consideration of storm water in the water tax brings a disproportion about the price between the different types of built-up areas such as single-family houses, multi-storey houses and commercial buildings. For instance, as shown on the figure 1 below, commercial buildings have large impervious areas where the amount of rainwater precipitation drained is more important that a single-family house which the surfaces of sealed areas is less important. However, regarding the amount of water drained on commercial buildings, they do not contribute as much as they should for storm water drainage as the existing water tax is based only on fresh water consumption and they have a very limited water usage.
Figure 1: Representation of the different types of built-up areas
Regarding this imbalance, this project proposes a new conceptual basis by restructuring the water tax. This new calculation would include storm water drained from the different types of properties with sealed areas whose are mainly single-family houses, multi-storey houses and commercial buildings. Only impervious surfaces connected to drain pipes are taking into account. The main purpose of this new calculation is to rebalance the price of water tax for each property regarding their impervious surfaces per square meter.
But what are the benefits of restructuring water tax for citizen? By including storm water in the water tax, this allows to make the fee more equitable for households as the new fee is related to impervious areas surfaces. It also attends to incentivize indirectly good practices among citizen to minimise the amount of rainwater going to drain by developing green infrastructures on their properties (harvesting water, green roofs etc.). But restructuring water tax benefits rainwater management as well. Indeed, by including storm water in the water tax, this allows to maintain, repair and replace the infrastructure.
In order to restructuring the water tax, a calculation of the rain falling on sealed areas is needed. For that, impervious areas such as concrete, asphalt, paved roads, buildings roofs etc. on each property has to be measured and demarcated. To calculate the rainwater, we disposed of input data. This input data is evaluated and analysed in GIS system and photogrammetry image. In InSell philosophy, the use of advanced technologies such as photogrammetry image, is essential to lead to a better and smart water management.
Figure 2: Demarcation of the impervious areas
Stage 2: Use photogrammetry and GIS to provide a logical basis
As mentioned above, the key to develop this system is having one go-to repository for all spatial (Geographic)and nonspatial( household and partly census) data. The spatial perspective and spatial analysis that GIS systems offer is essential to collect, manage, analyse and distribute information.. According to this perspective, geospatial data combine with advanced mapping technologies such as digital photogrammetry, orthophoto image etc. is efficiently used in developing the household level maps with heights upto an accuracy of 7-10 cm..
The figure In this part, we will then highlight our data processing workflow and methodology used to compile sealed areas in Photogrammetry systems.
Figure 3: Processing workflow
Stage 3: Preparing Proposal for citizen to calculate their own water consumption
There are many bottlenecks and challenges in this conceptualization and calculation of new water tax. Citizen are often asked to verify the compiled information about accuracy and correctness. Sometimes, they do not agree with the areas calculated by systemsand they have their own measurements of sealed areas of their own property (fill up different information => types of buildings, material used, size, characteristic of the buildings) then come into conflict with the concerned authorities. InSell along with its partner is developing a smarter solution to streamline this process for citizen. This solution will include geospatial web platform and client applications where citizen can fill up the required informationusing devices (PC, phones, laptop etc.). This app will have functionalities to even check the tax and water consumption according to the type of building, family size etc. This will have several advantages for citizen as well as municipalities to exchange information. This would also have a provision to add new areas or remove existing sealed areas from the property.
The concept note of this smarter water app will be presented in the separate blog on smarter water management.