Rain Water Harvesting (Part 2)

Domestic Uses

Helmreich and Horn Recommendations
The collection area's Helmreich and Horn recommended for domestic rainwater harvesting (RWH) include roofs, courtyards, and roads. GIS was predicted to be a useful tool in locating appropriate collection zones.

The most important aspect of the storage container is a tight lid that prevents contamination, algae growth, and mosquito breeding. They didn't have a definite recommendation for the location of the tank, above or below ground, nor the size of the container. Larger tanks were not inherently preferable as it took longer to cycle through water, so it's less fresh.

If drinking water is the aim of the harvesting, then open containers were not recommended. And collection sites in urban areas would need to filter out the air pollutants and roof contaminants.

Implementation Example
Bangladesh is looking toward rainwater harvesting as a potential solution to reduce urban flooding during the monsoon seasons and alleviate water shortages in the dry season. A study was conducted by Akter and Ahmed to access the potential for rooftop RWH in South Agrabad (southwest part of Chittagong city). They were able to demonstrate the value of GIS in analysing sites' suitability  for  RWH, as Helmreich and Horn predicted.  Factors considered in their model include the area of the roofs, the slope of the land, how easily runoff could flow, and the amount of drainage. (Elevation changes in the land was a factor that Hornreich and Horn emphasis for agriculture but not domestic collection.) South Agrabad was divided into 16 watersheds. Watershed one is lauded with rooftops being able to absorb .44 meters out of the 1.71 meters of total rainfall. Therefore Akter and Ahmed say that roof top rain harvesting can alleviate up to 26% percent of the flooding depth.

The possible amount of rainwater that could be collected in
each watershed compared to the current amount of runoff
in South Agrabad. Source: Akter and Ahmed

The 31% collection of total runoff in Watershed 10 was not considered a satisfactory reduction of water because the amount of stagnant water would still be above rickshaw height. The cause of additional flooding may be due to Watershed 10 being the lowest slope in the region. Excess runoff from other areas may accumulate there.

The amount of water each person could receive from roof water harvesting was calculated for 2006 (a dry year), 2011 (an average year), and 2014 (a wet year). They found that the daily amount provided by these collections was 20 liters per person.

Rain Water Harvesting Takeaways

The theme for both Africa and Bangladesh was using RWH to alleviate drought while reducing flooding. The principle applied to both agricultural and domestic water use. Helmreich and Horn briefly mention intense rainstorms, but they never delve into the benefits that water collection could have on reducing flooding risks.

It is interesting that Maswa, Tanzania used roads as a collection point, when Helmreich and Horn recommended it for domestic purposes. While the urban environment has more roads, they are a prominent feature of rural landscapes. It makes sense to take advantage of a surface material that causes runoff, which Helmrich and Horn see as a fundamental first step in RWH. Another reversal of recommendation occurred with South Agrabad, Bangladesh's use of land slope in their consideration of RWH sites. This might not have been considered a factor for Akter and Ahmed as they didn't consider any benefits inlvoving flood reduction.

Rain Water Havesting (Part 1)

The benefits of Rain Water Harvesting are not just in preventing runoff, as was mentioned in my World Soil Day post. It is also an important tool for softening the effects of drought.
Helmreich and Horn examined the potential for rain water harvesting (RWH) for both agricultural and domestic uses. This post will examine their findings with respect to agriculture and see an example of agricultural RWH. Next post will examine domestic RHW and compare it to the methods used in agriculture.

Agricultural Uses

Helmreich and Horn Recommendations
The two types of agricultural RWH mentioned by Helmreich and Horn were (1) water stored in the soil where it fell and (2) water collected away from the farm and stored away from the crops.
The initial requirement for a good collection site is a surface material that allows runoff. Additionally the slope of the land must be great enough to cause the runoff to flow.
The collection point could be above, below, or within the ground. Underground was recommend over above-ground structures as it prevents evaporation. If the water was to be stored within the ground itself, then the soil must retain water well.
It was recommended that local labour and materials were used to assess areas to adapt and build the necessary infrastructure.

Implementation Example

Maswa, Tanzania is a semi-arid region where a lack of rain can prevent crop growth and trap farmers in poverty. The crops may miss out on the benefits of up to 80% of rain, because they can't absorb it fast enough. RWH allows farmers to replace low-profit, drought resistant crops, such as Sorghum (a cereal), with high-profit, thirsty crops, like rice and vegetables. A study by Hatibu et al. looks at the economic benefits of different times of RWH systems. The examined Microcatments, Macrocatchments, Macro catchments paired with road drainage, and Macro and Microcatchments paired with pond storage. These RWH were mainly made local labor and materials (lots of earth ditches) as recommended by Helmreich and Horn. While the roads are not locally funded, the RWH systems branching off from them are locally constructed.

Really quick term definitions:

Typical microcatchment set-up. Source: Ali et al.

Microcatchments- small enhancements in the topography (eg. trenches) to increase the amount of water going to plants; Type 1 of Helmreich and Horn, which they highlight as cheap and local

 

Due to the lack of other jobs, economic benefit
(in US$) is best measured with respect to land
area. Source: Hatibu et al.

Macrocatchments- similar principles as microcatchment but for diverting large pools of water that accumulate during storms; Type 2 collection with Type 1 storage of Helmreich and Horn

Marcocatchments paired with road drainage- this diverts the pre-existing large catchment of water (used to prevent flash floods on roads) to crops; Type 2 collection with Type 1 storage of Helmreich and Horn

Macro and Microcatchments paired with pond storage- allows farmer to store water away from the crops and water them when needed; Type 2 of Helmreich and Horn


Hatibu et al. found that that Marcocatchments paired with road drainage was the most profitable in terms of US$ per hectare (land area).  This finding exemplifies the dual benefit of flood and drought alleviation that RWH can provide. The pond storage might be improved by the underwater storage recommend by Helmreich and Horn. The pond's higher potential for evaporation may be way it is so much less efficient than the road drainage.

Adaptation in COP

An agreement was reached at the end of the two-week negotiation. Source: Reuters

COP21 has drawn to a close. The broad impacts have been well reported, so I will examine how the COP agreement will affect adaptation.


The proposed actions to be taken before the agreement is enacted in 2020 include:

• Developed countries will create a solid plan to raise USD 100 billion for mitigation and adaptation that will begin in 2020, including an increased budget for adaptation (Paragraph 115)
• 2016-2020 will be a test period for adaptation technologies that increase resiliency, decrease vulnerability, and help enact adaptation (P125, 126,128)
• This will be a cooperative action that will examine what has worked in the past and offer specific solutions for the future (P128,129,130)
• A user-friendly online report will be summited annually (P130)

I think the test period for 2016-2020 is incredibly exciting. I'm glad that they will be reporting their result online in such a way that local government can support their adaptation.


The actual agreement included Article 7 that was all about adaptation. The highlights of this section include:

• Increasing resiliency, decreasing vulnerabilities while still developing in a sustainable manner (Paragraph 1)
• Focusing addition on those who are most vulnerable (P2)
• Decreasing emissions as a way to minimize future adaptations (P4)
• Recognizing that adaptation needs to be implemented in a 'gender-responsive' manner (P5)
• Using both scientific and traditional knowledge to create the best local strategies (P5)
• Sharing information on what has worked in the past, increasing scientific knowledge, and offering specific solutions for the future (P7)

I thought this was a very comprehensive plan for adaptation. I love that it is so closely tied to development, which is exemplified by their nod to adaptation that does not perpetuate forms of gender discrimination. I also appreciate the balance of scientific and traditional knowledge as locals will know the subtleties of their local environment.

Com'on Congress

Reactions from the COP21 climate conference are already popping up in the news. All eyes are on China and the US, the two top contributors of CO₂. The BBC recently praised China on their increase in renewable energy. As for the US.... The house has decided to pass legislation that would block the EPA's cap on coal emissions. It should be noted that 63% of the US population supports cutting emissions at coal powerplants.

House Speaker Paul Ryan sending a message
of dissent to Paris. Source: Yahoo!News

The Republicans held the vote on the SAME day as Obama's speech at COP21. They wanted to demonstrate their opposition, to any pro-climate remarks he made. The House Speaker Paul Ryan claims the benefits from any legally blinding agreement will not offset the high costs. It's beyond me why anyone would deliberately undermine their country's chance to demonstrate global leadership. Why should any other country, especially the developing ones, commit to cutting their emissions if we are unwill to cut ours?

Happy World Soil Day!

Today, December 5th, is World Soil Day!  Who knew?

One way to celebrate is to reduce runoff around your home. Run off and flooding can wreck havoc on topsoil. Limiting impermeable ground, making rain gardens, and harvesting rain with rain barrels are possible solutions to reduce runoff.

Keep fertile soil where it belongs. Source: GoSmith

Let it sink in: The inner workings of porous concrete

Permeable pavements, including porous concrete, are one of the solutions mentioned in the London Sustainable Drainage Action Plan. They are filled with little openings that allow rainwater to seep through to the soil. This should help reduce flooding. However, intentionally riddling a building material with holes is bound to produce some challenges. Engineers must balance how much water is allowed to flow through (conductivity) with the strength of the material.

How Porosity Affects Conductivity

The non-linear relationship between porosity and conductivity.
Source: Montes and Haselbach

Montes and Haselbach related the amount of holes in concrete (porosity) and conductivity. They used 17 samples of three different concretes to examine different porosities. Porosity was measured by comparing the weight of the concrete when it was dry to when it had been submerged in water for 30 minutes. They used a falling head permeameter to find the conductivity (a video of a similar experiment can be found here). They found a non-linear relationship between conductivity and porosity with a threshold at 15% porosity. Concrete with porosity lower than 15% didn't allow any flow.


Huang et al. used latex, sand, and fibers in concrete mixtures with aggregates (the little rocks in concrete) sizes of 12.5 mm, 9.5 mm, and 4.75 mm. They also used a falling head method to measure conductivity (aka permeability), but they used a vacuum seal to measure porosity.

Mixing concrete with other fillers cuts the permeability. Source: Huang et al.

Montes and Haselbach's curve predicted about a 20-60 mm/s conductivity for the latex, latex and sand, and latex, sand, and fiber mixes. The regular porous concrete should have had a conductivity of 80 mm/s. The actual permeabilities were consistently, considerably lower. The similar conductivities for the 3 add-in mixes shows that porosity should not be the only variable in Montes and Haselbach's relationship (equation on the 1st picture).

Creating Strength Despite The Holes

The fillers added by Huang et al. strengthen the concrete at the expense of a little conductivity. A mixture of latex and sand had both high permeability (compared to other add-ins) and high strength. Although, Huang et al. point out that their fiber wasn't thoroughly mixed.

A latex and sand mixture is both strong and permeable Source: Huang et al.

Yang and Jiang added silica fume (SF) and superplasticizer (SP), organic polymers, to their concrete. They measured a water penetration coefficient, similar to conductivity, to find out how quickly the concrete could absorb 20 mm of water. (They poured 200 mm of water and timed between 160 and 140 mm.) After performing a 28-day compression test, as opposed to Huang et al.'s 7-day test, Yang and Jiang produced an outdoor-cured  SF and SP concrete that had a strength of 58.9 MPa. The water penetration coefficient was only 2.9 mm/s. This demonstrates the potential strength of porous concrete, but the cost of the polymer may make SF and SP an unrealistic add-in. I foresee Huang et al.'s use of cheaper materials will make theirs more applicable, despite its weakness.

Porous concrete can help prevent pavement from becoming a river. Artist: Edgar Müller

Practising What I Preach: November Update

In 'Practising What I Preach' I revealed that my yearly carbon emissions are 9.04 tonnes. I decided to be more mindful of my footprint. I cut back on riding the bus 7-8 times a week to only twice a weeks. I way mindful of where my food was grown and tried to buy British goods. After a month of being aware of my contributions to I have reduced my carbon by... *drumroll*...



Source: Carbon Independent

.18 tonnes!

Oh.

That's not as good as I hoped. The quickest way for me to get those number down is to cut my miscellaneous spending (hygiene, books, phone, etc.) to well below average. With the holidays coming up, I'll need to get creative when gift-giving.