Régimen jurídico

The followed methodology in preparing this case study was based primarily on gathering information on six key variables: Rainfall Data, Determination of Irrigation Water Consumption, Water Demand, Determination of Green Areas with Active and Inactive Irrigation, Determination of the Roof Areas and Roofing Material.

3.2.1. Rainfall Data

The rainfall information must be collected from the closest weather station to the site under consideration and with the longest data extension possible, in order to reflect local climatic variations. To promote the system simulation process for probabilistic study, the longer the record length, the more reliable the results will be.

For this case study the data are initially collected from the Meteorological Station of Monte da Caparica. The reporting period is 25 years (series of daily precipitation), from which weekly series of precipitation data will be used to compute the balance of rainwater inflow volumes and the consumption of irrigation water (total of 1301 weeks).

In spite of the fact that daily rainfall series would produce results of greater reliability it

would require a very extensive data set, while using weekly precipitation series, the data set will be less extensive but still very significant and with the desired reliability, appropriate for display of long-term trend.

Despite being the closest station to the FCT, there are several gaps in available data between 1985 and 2009. Thus, these breaches were filled primarily with data from the Meteorological Station of Alcochete, since it is the second closest to the study area, and also with data from a rain sensor of the FCT, in existence since 2002, and with the data from Meteorological Station of Vila Nogueira de Azeitão.

All data from the meteorological stations were collected through the website of the SNIRH.

3.2.2. Determination of Irrigation Water Consumption

Since there are no meters for water consumed in irrigation, the determination of annual expenditures was made empirically through a field survey, which identifies all the existing irrigation equipment operating in the various sectors of the FCT Campus.

Once all the equipment was identified, the water flow of each unit was determined as well as its weekly operating period. For this to be achieved, the collaboration of the gardening team of FCT was crucial. In section 3.3.2 a detailed characterization of the existing irrigation system on campus is provided.

3.2.3. Water Demand

Water demand determines the amount of water needed for irrigation and consequently the storage requirements. The water demand over the year is not constant; therefore it is necessary to assess the monthly distribution rate of water requisites for green spaces irrigation.

3.2.4. Determination of Green Areas with Active and Inactive Irrigation

The identification of all green areas that exist in the campus was made by direct measurement of the same, from the existing drawings in AutoCAD format (Annex II) provided by the Rectory of the UNL and by the heads of the Projecto Campus Verde (PCV – Green Campus Project). However, since the available documents date back to 2004, some green areas had not yet been considered to integrate the mentioned

drawings. Therefore, the missing areas were measured using the measuring tool provided by Google Maps.

3.2.5. Determination of the Roof Areas

The determination of roof areas of the several buildings included in the FCT Campus was performed through AutoCAD drawings (Annex III), using the measurement tool provided by this software. The drawings in question were provided by the heads of the PCV.

3.2.6. Roofing Material

This variable is very important since it will influence the rainwater runoff and thus, the amount of water that can be potentially collected and conveyed to the storage tank.

This information was gathered through a direct field survey, with support from the Security Office on FCT Campus.

3.2.7. Determination of Reservoir Capacity

3.2.6.1. Rippl Method

The most commonly used method for tank dimensioning in rainwater harvesting, is the Rippl Method. It consists on the calculation of a storage volume required to ensure a regular flow during the most critical period of drought observed. It usually considers monthly series of precipitation data, with the most possible extension. In this particular case, weekly series of precipitation data will be applied (Annecchini, 2005; Tomaz, 2009).

For this method, the affluence inflow is deducted from the water demand flow, for the same time period. The maximum positive accumulated difference corresponds to the volume of the reservoir (Pereira et al., 2010). By this method, the tank usually presents an oversized volume, since it is dimensioned to meet demand during the most critical dry periods.

To accomplish the rainwater tank dimensioning by the Rippl Method, an Excel spreadsheet was used, which was based on collecting all the necessary data (Figure 26).

Figure 26 - Data required for rainwater tank dimensioning by the Rippl method.

 Column 1 – Reporting period time in weeks (1301 weeks).

 Column 2 – Weekly precipitation data.

 Column 3 – Total catchment area (roofs area).

 Column 4 – Total water inflow collected by the system. It is obtained multiplying C2 by C3 and by the runoff coefficient related to each roof surface (see section 2.6.1.1).

 Column 5 – Weekly water demand for irrigation, which varies according to the month.

 Column 6 – Difference between water demand and water inflow.

 Column 7 – Accumulated sum of the values obtained in C6. The maximum positive accumulated difference corresponds to the volume of the reservoir.