**8.1 Construction cost**

Open concrete drain is constructed of a mixture of aggregates and cement at a design ratio, and sometimes reinforced with iron bars. For a similarly sized trenchless drain the only construction material is sand or gravel put in place with no mandatory skill. A comparative cost analysis for the various dimensions and composition of drains using local market prices was carried out and the results are illustrated in **Figure 9**. It is observed, for example, that for a given dimension, a reinforced concrete drain is about four times (4x) more costly than a trenchless drain constructed of sand aggregate, outside labour cost. Open concrete drain requires properly designed culvert

**Figure 9.** *Cost comparison for various sizes of drains and component materials.*

at each crossing as against slab, if a trenchless drain is constructed. A culvert of known dimension is 10 times more costly than slab of the same size, [11].

#### **8.2 Maintenance cost**

A concrete drain requires regular cleansing for free flow of water to be sustained. But because of high cost of labour and equipment for the evacuation of the attendant waste, the maintenance could be done ones in a year and preferably at the onset of the rainy season. Comparatively trenchless drain requires grass cutting when overgrown to maintain its environmental friendliness. The maintenance is easily done at a desired time and at a relatively very cheap operational cost.

#### **8.3 Aesthetics**

Open concrete drain presents an unsightly view especially when it is not properly maintained. Sometimes it serves as an easy waste dump site for uninformed and carefree inhabitants. Comparatively, the greenish outlook of a trenchless drain merges with nature to beautify the environment and provides a healthy and sustainable scenario.

#### **8.4 Flooding**

Concrete drain is easily submerged in course of rainfall due to obstructions and low grade terrain. The water may remain stagnant for a good length of time, providing a good breeding ground for mosquitoes. This often results to exponential increase in malaria cases. Trenchless drain does not retain flood water for a period of over 1 hour after a torrential rainfall [12]. It therefore provides minimal opportunity for mosquito breeding. On heavily flooded roadway it is often difficult for road users to identify the limit of an open concrete drain and such persons may run the risk of falling into the drain. Trenchless drain provides, apparently, a continuous surface cover with no perceived danger to road users.

#### **8.5 Erosion**

Where an open concrete or pipe drain is functional its discharge can cause erosion at the outlet of the drain or its culvert, especially where the drain or culvert is not properly terminated. Over 240 well developed gully erosion sites in South East of Nigeria were observed to have been caused by wrong termination of drains and culverts [13]. The trenchless drain can hardly yield significant surface runoff that can initiate any form of erosion down slope.

## **9. Limitations**

